ESE's works engine tuner

[Frits Overmars]

F5Daves suggestion of using a ball bearing ball and punching it to form the valve set seems to work. I have a few Mikuni float valves so it could be worth a try.Shaping the valve seat with a bearing ball and a hammer definitely works.

[F5 Dave]

Drilling brass remember. Must try modified drill bits next time I do it.

[TZ350]

.

353358

Previous best ever dyno run with the F81M on Methanol.

Hopefully after I get the fuel flow issues sorted I will be able to pull these numbers or better consistently.

353357

Took a look at the F81M's 1970's transfer port layout. Good news, it looks like there is a bit of room for improvement.

[TZ350]

.
The making of a Methanol 4,2mm ID float valve for a Mikuni VM34.

353362 Relative differences in length between a Dellorto and Mikuni float valve assembly.

353361 Thought I would go the hard way and insert the Dellorto into the Mikuni.

353360 Finished assembly. Hard to see in the picture but there is a reasonable relief around the Mikuni float valve body for the Dellorto fuel holes to open into.

353367 Mikuni Methanol carburetor with enlarged fuel passages, Dellorto float valve and Wobbly adjustable power jet.

[oldjohnno]

Holley bowls are way better than anything else I've tried, if a bit bulky. Big flow rates, able to withstand fairly high pump pressure and not upset by vibration. Also externally adjustable float height and a variety of seat sizes and needle materials available.

[husaberg]

Holley bowls are way better than anything else I've tried, if a bit bulky. Big flow rates, able to withstand fairly high pump pressure and not upset by vibration. Also externally adjustable float height and a variety of seat sizes and needle materials available.

Very Nice
Cool adjustment procedure for these carbs also.

https://www.youtube.com/watch?v=ge-mIk6nEYQ

[oldjohnno]

I might just add a few thoughts on methanol with 2T engines, based on what I found running it in my LSR bike both on the salt and on the dyno. I had issues with consistency in both setting; usually what would happen is it would start a run fine then after maybe 5 or 10 seconds it would lean out, despite having a more-than-adequate supply.

It took me a long time to work out what was going on but eventually I found that fuel was collecting in the crankcase. Methanol tends to drop out at idle and low speeds, so it needs additional richness in the low speed circuits to compensate. Like most people I usually blip the throttle for a bit before a dyno run as a quick warmup, or if I'm sitting at the start line waiting to go I'll idle and maybe blip it a bit. While I did this, fuel was collecting in the crankcase, though I was completely unaware of it. It occurs quite quickly, and because the engine never really got hot it's persistent. The puddled fuel is consumed when the throttle is opened and the revs increase, this fuel being added to what the main circuit is supplying.

The problem is when you jet - if the duration of the run isn't long enough (and this is especially likely with an inertia dyno) a jet will be selected that will provide the right amount of fuel so long as it is being (unknowingly) supplemented by the puddle downstairs. If the dyno runs are short everything will seem fine and it'll make good power. But in a long run on the dyno or on the salt it would lean out every time. Some people suggested it was temperature related but that turned out not to be the case.

I added a handlebar mounted control that let me manually enrich the main circuit when it began to lean out, and this worked but it was a kludge. Later, I added individual needle valves between both the idle and intermediate discharge holes and the float bowl, to give better control of part-throttle mixture. This worked well, but I found that if the engine had been idling I could shut these valves right off - completely isolating the fuel supply - and the engine would continue to run for quite some time afterwards. That's when it all started to make sense.

Eventually I added a very small tank under the carb that supplies petrol to the idle/transfer circuits (directly with no float bowl). This completely eliminated the problem and jetting is now consistent no matter how long or short the run is. The main circuit runs methanol and is inactive at small throttle openings. As a happy side-effect the petrol helps put a little heat into the engine (which the methanol loves) and it automatically purges the alky after a run.

It's probably over-complex and impractical for most applications but for me it meant the jetting could be set accurately with confidence and the engine ran consistently every time.

[TZ350]

.

Fuel dropout in the crankcase at low rpm, makes sense. I had that issue when I tried running a plenum. Fuel would trop out in the plenum. Surprising amount too. Fuel dropout killed off the plenum idea. A small petrol supply to the idle/transfer circuits sounds like a great way to get a clean running Methanol two stroke. I will look into it. Thanks.


259989 259990

This is the arrangement that I tried ages ago to get around the restriction of a 24mm carb. The idea was that the motor sucked from the plenum through a big unrestricted inlet and the 24mm carb had plenty of time to refill the plenum between suction events.

[TZ350]

Eventually I added a very small tank under the carb that supplies petrol to the idle/transfer circuits (directly with no float bowl). This completely eliminated the problem and jetting is now consistent no matter how long or short the run is. The main circuit runs methanol and is inactive at small throttle openings. As a happy side-effect the petrol helps put a little heat into the engine (which the methanol loves) and it automatically purges the alky after a run. It's probably over-complex and impractical for most applications but for me it meant the jetting could be set accurately with confidence and the engine ran consistently every time.

Methanol for the main jet and petrol for the idle/transfer circuit. It might prove to be overly complicated and impractical but looks like a very good idea worth exploring.

353438 353440 353439

For road racing I probably need to have a bit of petrol handy for the longer races. So, I found this small diaphragm pumper carburetor from a four stroke weed eater. Plenty of places to hide it on the 250. After modifying the carb by cutting the un necessary bits off. I could mount a small tank and gravity feed the pumper with a small line running from it to the Mikuni's idle/transfer circuit.

[Grumph]

You're starting to get to the point where it may be less complicated to go back to the injection...

As a matter of slight interest, the speedway TQ's I tuned - all 4T fours - I ran the carbs slightly lean at idle.
Under a caution light circulating slowly, they stayed warm and didn't load up.
The guys running Hilborn injection were invariably slow off a caution as they couldn't lean them out.

[F5 Dave]

Might run fouls of pre72 rules there. Lean on idle can only mean lean on pilot on a slide carb. Seize city on 2 stroke roadrace. Closed throttle high revs for several seconds.

Well, at least on petrol. Maybe enough meth to not?

[TZ350]

You're starting to get to the point where it may be less complicated to go back to the injection...

Electronic Fuel Injection would absolutely be my choice for an alcohol two stroke engine. But sadly EFI is specifically forbidden for pre 72.

[Grumph]

Eventually I added a very small tank under the carb that supplies petrol to the idle/transfer circuits (directly with no float bowl). This completely eliminated the problem and jetting is now consistent no matter how long or short the run is. The main circuit runs methanol and is inactive at small throttle openings. As a happy side-effect the petrol helps put a little heat into the engine (which the methanol loves) and it automatically purges the alky after a run.

It's probably over-complex and impractical for most applications but for me it meant the jetting could be set accurately with confidence and the engine ran consistently every time.

Don't need the diaphragm pump. For a roadrace application I'd use a small float chamber alongside the carb supplying petrol/oil mix to the idle circuit only.
So metering is still through the one carb and though two fuels are used, no rules are offended.

Only the KISS principle.

[F5 Dave]

So. . If you made a float drain plug that had a pipe that sealed with a rubber tube to the pilot jet. . . Pause for Thinking. . And that lead to a secondary Float bowl because you don't want to flood it or starve it. . . You could have another carb bottom fed petrol. If that was mounted on a slide mount you could adjust the level to something that works ok.

And if you are really careful won't be a fire risk when crashing.

[Strokerhaus]

You're starting to get to the point where it may be less complicated to go back to the injection...

As a matter of slight interest, the speedway TQ's I tuned - all 4T fours - I ran the carbs slightly lean at idle.
Under a caution light circulating slowly, they stayed warm and didn't load up.
The guys running Hilborn injection were invariably slow off a caution as they couldn't lean them out.

Ive had similar experiences with 4T speedway bikes, whilst tuning carbs for gating after less than 10 stop starts without any runs in between we had washed the bores. Take care with very short dyno runs.

[oldjohnno]

So. . If you made a float drain plug that had a pipe that sealed with a rubber tube to the pilot jet. . . Pause for Thinking. . And that lead to a secondary Float bowl because you don't want to flood it or starve it. . . You could have another carb bottom fed petrol. If that was mounted on a slide mount you could adjust the level to something that works ok.

And if you are really careful won't be a fire risk when crashing.

Given that most slide-type carbs have a float bowl that is barely adequate at best for alky - except for quite small engines - I'd go the other way. The stock bowl and float valve would handle the idle and off-idle duties easily while a more competent external bowl could handle the alky for the main circuit. I don't use any float bowls (butterfly style carb) - the lo speed circuit pulls directly from the small tank below the carb while the main circuit is fed directly from the top main tank via a barrel valve linked to the throttle and a pill.

I haven't tried it yet but I think the petrol-part-throttle setup would work very well with nitro. I've only played very briefly with it but it's a bit like methanol in that it needs heat, pressure and a load to burn properly, only much more so than methanol. It hates a light load and less than W/O throttle, and besides it make no sense to be burning expensive nitro when it isn't necessary.

[Pursang]

Given that most slide-type carbs have a float bowl that is barely adequate at best for alky - except for quite small engines - I'd go the other way. The stock bowl and float valve would handle the idle and off-idle duties easily while a more competent external bowl could handle the alky for the main circuit.

I think that's very clever!

[SwePatrick]

To add to methanoldiscussion:

I don´t see the problem as discussed, but it may very well be.
I see it another way though.

When reaching a certain engine temprature you start to vaporize the fuel better, before this the engine runs bad and seems rich.
This due to the combustion isn´t good, actually not good at all.
A methanol engine the first seconds after startup is very dull and tired.

64.7c is methanols boiling point.
Petrol has a boilingpoint of 30-190c depending on pressure(i guess)
This is in direct relation in how easy it is to start an petrol engine versus an methanol engine.

[Pagi]

Once again Frits is on the money.
My empirically derived idea of exhaust duct exit reduction to 75% of the effective Exhaust Port area works very well as a guide to the size to be looking for.
Frits has always maintained the exit area should be tied to the Blowdown capability.
Here we have a case of the Blowdown , that is optimized to achieve a relatively modest 13 Bar bmep , achieves Mach 0.8 at the pinch point with a 71% area reduction.
Smaller looses power as does a larger exit diameter.
It seems the only way to optimize this factor is by tracking the Mach number to achieve 0.8.


Wobbly,

does this Mach number (0.8), is a value that must be taken into account for a single exhaust duct ? ( around 90% area reduction, if i remenber correctly)

[wobbly]

The 90% area for a single Ex is a pointer , but the whole idea was developed in the scenario where you have a huge amount of 3 port Blowdown area initially dumping into an oversized duct volume.
With all that Blowdown the BMEP is high obviously , and thus the bulk gas flow at peak power is also very high.
But in a single Ex port we are never going to get close to those Blowdown numbers , nor the BMEP , and thus the power delivered.
From memory I havnt seen a single Ex project where it was possible to achieve 0.8Mach before power was lost due to the exit getting too small.
All you can do is start at 90% and move down in area until you loose power - then go back a step.

Re the Methanol burning engine problems , all I can say is that we ran a 60 Hp 150cc bored out TM-MX engine for years in open class with a 41mm Dellorto carb using the 4.2 float valve and a diaphragm pump
set with a return line jet to give 18" of pressure head above the carb bowl ( as a tank would give on a bike ).
We never had any tuning issues with dropout or any weirdness of any sort , except having needle ends dropping off from being spun down too thin.
This was solved with the adjustable powerjet that replaced 25% of the main jet flow ( 1mm dia powerjet with a 2mm main ) and thus the needle didnt need to be thinned so radically.
Later we went to a 250cc MX engine using the same carb , and just had to redrill all the jets slightly bigger and use a 4,5 float jet to keep the bowl full.

[Niels Abildgaard]

Some serious austrians are working to design and dominate the market for EV range extender .

https://www.fvt.at/ka/en/references/layout-and-design-of-an-innovative-range-extender-engine.html

It is a two stroke with side exhaust valves and no charge through crankcase.
They claim it is a must for three-way catalyst after treatment.
I do not understand and will love to.
A gentleman here was working with the Orbital and they must have seen the problem.
What is his entry name here?

[Frits Overmars]

Some serious austrians are working to design and dominate the market for EV range extender .
https://www.fvt.at/ka/en/references/layout-and-design-of-an-innovative-range-extender-engine.html
It is a two stroke with side exhaust valves and no charge through crankcase. They claim it is a must for three-way catalyst after treatment. I do not understand and will love to. A gentleman here was working with the Orbital and they must have seen the problem.
What is his entry name here?The same as his name in real life: Ken Seeber.

[Niels Abildgaard]

The same as his name in real life: Ken Seeber.

Hello Nightraven
Thank You and I will ask him tomorrow.
Sleep well

[wobbly]

Whaaaaat Frits , you mean there is a " real life ".

[TZ350]

The stock bowl and float valve would handle the idle and off-idle duties easily while a more competent external bowl could handle the alky for the main circuit.

I have had a good look at one of my Mikuni carb's and it looks like the petrol through the original float bowl for choke and pilot jet duties. And an external methanol float bowl feeding through Mikuni's float bowl nut to the Mikuni's main jet would be easiest way to go.

353446

This Mikuni has a brass shield around the main jet. I guess it's purpose was to reduce fuel surging away from the jet when moto crossing over Jumps and rough ground. Anyway it looks like it will be helpful in retaining some sort of sealing arrangement between the fuel bowl nut and the main jet. Looks easy.

Does anyone have a matchbox or other remote float bowl they would sell?

[F5 Dave]

Is there room for a second carb off to the side? Cut the top off and seal drillings, bar of course a dirty big breather hose up out of the way.

Um, like that Delorto.

[Grumph]

Does anyone have a matchbox or other remote float bowl they would sell?

I've used matchbox float chambers and while the size is convenient, I'd doubt if capacity or flow rate would work. They're also very sensitive to vibration.

Bite the bullet and find an old SU chamber. If i can find it post move I may even have one here.

[oldjohnno]

Re: SU bowls - float bowls from an Amal concentric or Mk2 would also be a good choice - the float valve is part of the bowl so they'd only need a flat cover plate that could also incorporate a mount. But if you really need a lot of fuel you can't beat a Holley bowl. They'll handle 7 psi of pump pressure no problems but they're a little bulky.

[TZ350]

Bite the bullet and find an old SU chamber.

Ok, I have found a SU float chamber. Certainly looks like it can be made to do the job.

[Grumph]

Ok, I have found a SU float chamber. Certainly looks like it can be made to do the job.

Can i suggest a swill pot on the opposite side of the carb to the float chamber. IE - chamber in front of the carb (front of the bike) and a small swill pot behind.
Doesn't need to be very big at all - make it from something like a piece of 3/4in stainless tube.
Ensures the mainjet is not affected by braking and acceleration.

[wobbly]

All way complicated and not necessary , the Dellorto had a 10mm long main jet extension that screwed into the emulsion tube end , and an extended float bowl bowl nut.
Never had any issues at all.

[Frits Overmars]

All way complicated and not necessary, the Dellorto had a 10mm long main jet extension that screwed into the emulsion tube end, and an extended float bowl bowl nut.Something like this? And with ultra-open foam (the red stuff) to prevent frothing? :msn-wink:
353453

[TZ350]

All way complicated and not necessary.

Yes, in the end, the complication may kill the twin fuel idea. But the idea intrigues me. So I would like to prepare a second carb as a comparison. I have some time as I am unable to use the dyno for a while. There is a freshly painted classic Ford pickup parked behind the dyno getting its final touches and no ways am I going to risk blowing a paint pealing mixture of two stroke exhaust over it.

[katinas]

Some pictures of the latest KTM SX 125 EFI engine.
Crank plastic inserts screws must be checked and "re loctited" as they have a tendency to loosen after few rides.

[Tim Ey]

Some pictures of the latest KTM SX 125 EFI engine.
Crank plastic inserts screws must be checked and "re loctited" as they have a tendency to loosen after few rides.

Really interesting hamster cheeks in the crankcase. If I recall correctly, the 2017 SX did not have that. Whats the reason?
- pre compression ratio increase?
- better flow out of reed?
- extention of the back B-Port wall?
- all of the above?

Regards
Tim

[husaberg]

Really interesting hamster cheeks in the crankcase. If I recall correctly, the 2017 SX did not have that. Whats the reason?
- pre compression ratio increase?
- better flow out of reed?
- extention of the back B-Port wall?
- all of the above?

Regards
Tim
They likely could also not get enough material off from the inside whilst supporting the pin.
thats seems to be a large wall thicknes on the pin.
#The early at least 85's tend to melt the inside stuffers.

edit sorry i thought you meant the crank not the cases:o

[TZ350]

.
353462 353460 353461

Making good progress on the Meth-Petrol-Carb. Sealing ring in the float bowl nut. Petrol in the carb and methanol in the remote float chamber.

Petrol for the primary fuel circuit and methanol for the needle and main jet.

The remote float chamber has 5,5mm galleries and a 4,2mm float valve.

Next move is to add an adjustable methanol power jet and fuel level indicator like the one on the straight methanol carb.

353463

Straight methanol carb with Wobblys Dellorto 4,2mm float valve and adjustable power jet. The fuel level can be seen in the clear tube.

[F5 Dave]

Oh yeah. Forgot it is Rotary so side of engine.

[TZ350]

.
353464

The completed petrol/methanol carburetor with adjustable power jet.

[koenich]

Really interesting hamster cheeks in the crankcase. If I recall correctly, the 2017 SX did not have that. Whats the reason?
- pre compression ratio increase?
- better flow out of reed?
- extention of the back B-Port wall?
- all of the above?

Regards
Tim

this was done so some "tuner" can regrind the cases, cut the head, recommend to use 190 octane fuel and make a story how it now revs to the moon.

kidding aside, I'm sure KTM had a reason to do so - would be interesting to know it, all your reasons make sense.

[katinas]

Really interesting hamster cheeks in the crankcase. If I recall correctly, the 2017 SX did not have that. Whats the reason?
- pre compression ratio increase?
- better flow out of reed?
- extention of the back B-Port wall?
- all of the above?

Regards
Tim

Yes, looks like these crankcase "glands" match the flow from V force type reed block very well. But the last carb engine tuned version, still have 4-5 hp more and it is very noticeable on the track.
Without easy possibility to change fuel rate on EFI engine, tuning is complicated.

[F5 Dave]

Ready to Race.

With an arm tied behind your back.

[TZ350]

But the last carb engine tuned version, still have 4-5 hp more and it is very noticeable on the track. Without easy possibility to change fuel rate on EFI engine, tuning is complicated.

That is interesting, KTM carburetor engine makes significantly more power than the EFI version. My experience with two stroke EFI is that you can easily match or better a carb engine for maximum power and over rev. With access to the fueling maps EFI is so easy.

[Grumph]

That is interesting, KTM carburetor engine makes significantly more power than the EFI version. My experience with two stroke EFI is that you can easily match or better a carb engine for maximum power and over rev. With access to the fueling maps EFI is so easy.


Neutered by having to meet Euro emissions regs ?

[TZ350]

.

I am not sure why 2S EFI should find it harder to meet Euro standards than a carb engine.

Flettner who has way more real world practical riding experience with 2S EFI than me. Reports that with transfer port injection (TPI) there is a noticeable fuel saving which would suggest there is less fuel wasted through charge short circuiting. That has to mean a cleaner engine exhaust.

KTM copied Flettners TPI idea then went to reed port injection. Injecting before the reed valves looks like a poor mans carburetor to me. With all the problems of a crankcase full of fuel mixture, some of which is lost through short circuiting.

Again from my 2S EFI experience. A 125 is much harder to map properly than a 300. I suspect, maybe KTM has found mapping a 125 for the vastly more dynamic on pipe/off pipe conditions a challenge. There is a way but it is much more tricky than working with a 300.

[Peter1962]

That is interesting, KTM carburetor engine makes significantly more power than the EFI version. My experience with two stroke EFI is that you can easily match or better a carb engine for maximum power and over rev. With access to the fueling maps EFI is so easy.

On the ktmtalk forum there are a lot of stories on problems with the SX125 with failing crankshafts since model 2022. Some think that KTM did not properly solved the problem, but in stead limited the Maximum RPM on the TBI 125 SX model 2023 to avoid catastrophic failures... Poor choice. https://ktmtalk.com/threads/2023-125-sx-crank.569456/

The ktm 125 model 2022 had more HP than the model 2023.

But the 250 SX TBI 2023 has more HP than the previous model, so I do not think that it depends on the injection but rather to the choices that the ktm engineers implemented concerning the mapping.

[husaberg]

You have to love the irony that nearly 15 years ago ktm had injection on their 2 stroke gp bikes that worked on overrun to avoid crankshaft failures......
353468353469353470353471353475

The most important thing, however, is that the injection enables things that are not feasible with carburettors alone under certain load conditions, such as overrun or in the partial load range. Knock sensors in the cylinders can detect and compensate for minor inaccuracies in the spraying. In addition, it is possible to drive much leaner in the partial load range and also to lean individual load and speed ranges in a targeted manner, which improves drivability and torque curve

[katinas]

.

I am not sure why 2S EFI should find it harder to meet Euro standards than a carb engine.

Flettner who has way more real world practical riding experience with 2S EFI than me. Reports that with transfer port injection (TPI) there is a noticeable fuel saving which would suggest there is less fuel wasted through charge short circuiting. That has to mean a cleaner engine exhaust.

KTM copied Flettners TPI idea then went to reed port injection. Injecting before the reed valves looks like a poor mans carburetor to me. With all the problems of a crankcase full of fuel mixture, some of which is lost through short circuiting.

Again from my 2S EFI experience. A 125 is much harder to map properly than a 300. I suspect, maybe KTM has found mapping a 125 for the vastly more dynamic on pipe/off pipe conditions a challenge. There is a way but it is much more tricky than working with a 300.

Factory set just two fuel mapping programs and looks like one lean, other even more leaner.
The only change that we done with EFI engine, new head insert with corrected squish to 0.8 mm ( 1.2 mm from factory with 12 cc volume) and 12 angle 3mm piston dome.
This add 1.2 hp.
Crankcase pressure sensor connected directly to C port through 16 mm pipe.

[TZ350]

Crankcase pressure sensor connected directly to C port through 16 mm pipe.

The way the KTM's EFI software makes use of the pressure readings interests me. I would love to know more about that.

[koenich]

Someone on VitalMX posted the below info...


There is a series of “tables” that are related to each other, mathematically, that effect each other, and adapt to each other that related to ignition timing, fuel delivery and pv.
It is all based off the TPS and any changes to the engine (by use, intentional mods such as external TPS adj, wear and tear etc), and the tables attempt to compensate for these changes automatically, they hold their value, and sometimes for the worse.
Simply put, if you log 25 hrs on your top end, at some point during those hours, the wear and tear has effected the cps and changed the pressure under the piston, this has effected the way your ride, it made more heat, all the while the tables morf to attempt to compensate what it can to get it back to what it considers it’s zero point.
The tables shift and hold onto that value, it has “adaptive learned”.
You put in a top end and leave all as is, the ecu may still consider it’s held values it learned..this is why it is so important to clear the adaptive shift and get the engine back to its electronic zero so it’s baseline is restored.
This process to me is more important to the pv reset or anything else at this point.
The changes it morfs to can never go to an extreme and eventually it hits a wall and can’t move any more.
This is where if all those negative engine attributes stay held, the performance gets worse and worse.
The ex) of TPS adj has now changed my mind about how it is done.
If the TPS is adj, you are shifting the table of timing, fuel and pv, they are connected like a chain.
In very small movements, it will only effect the tables slightly, however as the engine started to wear down, the morfing gets more pronounced and “held”, or remembered.
This is also true with the sensing capabilities of the engine, it has held values determined by the sensors.
If you go down the the line at 9am for mx practice and it’s 45 deg, go back to the truck and shut it off and leave it until 1pm and start your bike on the line, your motor held the 45 degrees and will run that way until it catches up with itself after it learns.
What I would recommend in this situation if it’s 1pm, start your bike at the truck and let it run and blip for 20 seconds and then shut it off…then go to the line.
Your sensors will absorb the new data that it’s warmer and adapt.
This is one of the tables that has an X-Y axis as in engine rpm and throttle opening.
All those cells have cross over points over certain rpm ranges that effect each other.
Move one area, it shifts the table to effect fuel, timing, pv, etc.
I’m just getting the hang of the cause and effect of this but I can tell you one thing.
As for the actual combustion process of a two stroke motor with a pv, this is super simple….same same.
Regarding the fuel delivery, pv, timing, tps, crank pressure, etc throw everything you consider the “same” as a carbed bike out the window.
They are now two different things and should be treated that way, I have much more to share but am trying to keep it super easy to say and think about how to say it.
Stuff the cases with epoxy and dont compensate for that increase presssure under the piston with the ecu? It will also increase the velocity, lean out your fuel delivery and you will explode you motor..it’s that sensitive, unreal.
More soon- sorry if this is wordy, I’m learning and sharing at the same time lol.
Clear the adapted learned changes from your bike all the time and especially when large scale engine changes have occurred like top ends and if large environmental changes happened like cold am motos and hotter pm motos.

Source: https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/2023-KTM-125SX-deep-dive-EFI-tune-mods-exploring-the-tech,1408609?page=5

I don't know any better but this would be an extremly complex system w/o much benefit. My best guess is it senses load by a fast pressure transducer and has some sort load depending alpha-N mapping.

[TZ350]

.

Thanks.....

[_____]

Source: https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/2023-KTM-125SX-deep-dive-EFI-tune-mods-exploring-the-tech,1408609?page=5

... My best guess is it senses load by a fast pressure transducer and has some sort load depending alpha-N mapping.

If I would need to bet my money, I would say the sensor in the boostport is a transducer that collects crankcase pressure in two or more points of engine rotation. When the sensor also has a temperature probe installed, you are able to calculate the filling of the crankcase with the ideal gas equation.
https://en.wikipedia.org/wiki/Ideal_gas_law
Because you have certain knowledge of t, p, V. The values for M and R might vary with AFR in the crankcase, but I think that is minor and might be adjustable with measuring twice.

So say they got that under control: When they know how much air mass (with fuel) is in the crankcase, it is possible to add the required fuel to it.

When you combine that with an Alpha-N map for acceleration and use the calculation of the air mass in the crankcase, you may either inject according to the ideal gas law, or reduce your acceleration quantity with a fudge factor coming from the gas law equation.


Regarding the MX guy:
I doubt they have self learning in that depth because it would not make any sense. However, I have not ridden the bike.

Regards
Chris

[dutchpower]

ecu 125 sx 2023

[Flettner]

The original YZ250TPI would run between 14 and 21% less fuel burnt than a standard, same spec, carburetor YZ.
Compared same days, same tracks, aulternating riders, over many events. Same top end power.
14% on the more open fast events, 21% was seen at slow low speed events.
One would have to conclude that that's a funtion of less fuel short circiting out the exhaust. Also partly because the engine would sort of be a stratified charge combustion at lower speeds with fuel only entering the B ports. A decient squish and toridal head seemed to help with this last ditch fuel / air mixing. Power is definitely more mellow down low in the rev range compared to the carburetor bike. Interestingly I could turn in a faster time on the TPI bike but the carb bike felt faster. Way more linner power delivery with less ' surprises'.

[SwePatrick]

I thought i´d share this with you guys:


https://www.youtube.com/watch?v=cQTbneBNqok

I had some problems with the chain didn´t feel the urge to stay in place.
Need to mount the engine solid(now it is rubber hinged) and reinforce the rear swingarm.

So we couldn´t push it as hard as we wanted to.

[Wos]

The original YZ250TPI would run between 14 and 21% less fuel burnt than a standard, same spec, carburetor YZ.
Compared same days, same tracks, aulternating riders, over many events. Same top end power.
14% on the more open fast events, 21% was seen at slow low speed events.
One would have to conclude that that's a funtion of less fuel short circiting out the exhaust. Also partly because the engine would sort of be a stratified charge combustion at lower speeds with fuel only entering the B ports. A decient squish and toridal head seemed to help with this last ditch fuel / air mixing. Power is definitely more mellow down low in the rev range compared to the carburetor bike. Interestingly I could turn in a faster time on the TPI bike but the carb bike felt faster. Way more linner power delivery with less ' surprises'.


A narrow squish helps every 2 stroke to reduce the consum of fuel!

For example:
We reduced squish on a yz 125 to 0,7 mm and had to lean the mixture ;)

Effekt... better throttle reponse...more power everywhere...consumption went down

My opinion...

If you have large squish often it is difficult or nearly impossible to find a satisfying setup for the carb...cause of low MSV...
which leads to low burn velocity...and that makes it necessary to richen the mixture up...

All the same on a yz 250..

Your experiences welcome to widen my horizon ;)

Grüße ;) Wolfgang

[wobbly]

Increasing MSV has two effects on combustion.
Firstly it increases the turbulent eddies that impinge on the expanding flame front , thus increasing the burn speed across the chamber.
This is analogous to advancing the ignition timing , without the down side of increased pumping losses on the way to TDC after the spark kernel has formed.
Secondly the reduced vertical clearance decreases the volume of end gases trapped in the squish area , thus making more A/F mixture available to burn earlyer
within the cycle - increasing the combustion efficiency.
All in all a win win , and a rare free lunch.

[Pursang]

All in all a win win , and a rare free lunch.

Not too often that Wobbly offers us a "free lunch" :woohoo:

[husaberg]

Not too often that Wobbly offers us a "free lunch" :woohoo:

He has offeredto do more than just buy your dinner....:innocent:

Long time ago ,if I remember correctly , I said free blowys for life to anyone making over 30Hp at 10500 in a bucket - cant remember if that was 100cc ( with 24mm carb ) or 125 aircooled.
No ones even come close, so I am safe, for now.

12 bar i think?

[oldjohnno]

I've long been interested in chamber design. In the four-stroke world modern engines with shallow pent-roof chambers utilise tumble to promote fast flame propagation, with little or no squish/quench. Spark timing is typically around 20deg for these, about half of that used in many older closed-chamber engines.

I always thought the transfer flow in a 2T would promote as much motion as these current 4Ts, possibly more. As an experiment I machined a head with a roof that matched the slight dome of the piston crown, so that the chamber was a simply a slightly dished disc of constant thickness. I made it the same volume as the two heads I'd previously run, the first one having a traditional 50% squish band and a roughly hemispherical central bowl. The second had about a 35% area band and a low flat roof and performed slightly better.

On the dyno the new, open chambered head was surprising. It wanted exactly the same spark timing as the other heads and torque and peak hp was about 3% or so higher. Also surprising was the fact that it wanted significantly less fuel - about 4% or 5% less. However it wouldn't tolerate richness like the other heads would. Where they would run with jetting in excess of the optimum with little loss of power the open chambers output would drop much more rapidly with excess fuel. I don't know if these results are a weird anomaly or not but I was pretty happy with it overall.

In the 4T world the trend has long been away from squish and towards shallow, open chambers. Mainly driven by emissions requirements I think and the need to reduce UHCs. With these it's not squish that's the problem, it's the quench that goes along with it. And because the two are inseparable it's hard to tell what causes what. I kinda suspect the benefits of tight clearances are as often as not because of the reduced quench volume rather than mixture motion.

[Frits Overmars]

I machined a head with a roof that matched the slight dome of the piston crown, so that the chamber was a simply a slightly dished disc of constant thickness. I made it the same volume as the two heads I'd previously run, the first one having a traditional 50% squish band and a roughly hemispherical central bowl. The second had about a 35% area band and a low flat roof and performed slightly better.
On the dyno the new, open chambered head was surprising. It wanted exactly the same spark timing as the other heads and torque and peak hp was about 3% or so higher. Also surprising was the fact that it wanted significantly less fuel - about 4% or 5% less. However it wouldn't tolerate richness like the other heads would. Where they would run with jetting in excess of the optimum with little loss of power the open chambers output would drop much more rapidly with excess fuel. I don't know if these results are a weird anomaly or not but I was pretty happy with it overall.How did you establish the fuel consumption Johnno? By jet size, by measuring the fuel flow velocity, by weighing the consumed quantity of fuel per minute?

[oldjohnno]

How did you establish the fuel consumption Johnno? By jet size, by measuring the fuel flow velocity, by weighing the consumed quantity of fuel per minute?

Ah, you got me. It was by jet size, so I can't really say it used a lesser mass of fuel. Still, it'd take a pretty significant increase in venturi signal to produce the same flow with the smaller jet. I should retest with better measurements.

[Wos]

I've long been interested in chamber design. In the four-stroke world modern engines with shallow pent-roof chambers utilise tumble to promote fast flame propagation, with little or no squish/quench. Spark timing is typically around 20deg for these, about half of that used in many older closed-chamber engines.

I always thought the transfer flow in a 2T would promote as much motion as these current 4Ts, possibly more. As an experiment I machined a head with a roof that matched the slight dome of the piston crown, so that the chamber was a simply a slightly dished disc of constant thickness. I made it the same volume as the two heads I'd previously run, the first one having a traditional 50% squish band and a roughly hemispherical central bowl. The second had about a 35% area band and a low flat roof and performed slightly better.

On the dyno the new, open chambered head was surprising. It wanted exactly the same spark timing as the other heads and torque and peak hp was about 3% or so higher. Also surprising was the fact that it wanted significantly less fuel - about 4% or 5% less. However it wouldn't tolerate richness like the other heads would. Where they would run with jetting in excess of the optimum with little loss of power the open chambers output would drop much more rapidly with excess fuel. I don't know if these results are a weird anomaly or not but I was pretty happy with it overall.

In the 4T world the trend has long been away from squish and towards shallow, open chambers. Mainly driven by emissions requirements I think and the need to reduce UHCs. With these it's not squish that's the problem, it's the quench that goes along with it. And because the two are inseparable it's hard to tell what causes what. I kinda suspect the benefits of tight clearances are as often as not because of the reduced quench volume rather than mixture motion.

My understanding

Mixture motion or call it turbulez...the higher the better.

Made some reserch at fraunhofer to burning behavior of coal dust in air

Result was exactly same

One coal particle somewere is beginning the process of burning...the higher its "SPEED" the more other particles crossing its way and are ignited too...and so on.

small number of particles need more turbulez...

Lot of particles and high turbulenz was leading to explosion ...

Reason for research was to avoid accidents in coal mines ;)


Grüße Wolfgang

[jonny quest]

Why did the oems use cl8se to 2mm of squish on YZ250 and CR250?

[philou]

reliability.

accepts any fuel. even expired

[Wos]

Why did the oems use cl8se to 2mm of squish on YZ250 and CR250?

Thats a good question ;)

Yz has a huge squish gap...
after reducing to about 1mm same compression the Charakter was very aggressiv...difficult to handle that power for amateur user

And that while The yamaha ignition curve is very conservative...only 23 degree to 3500...then falling quickly

Exhaust timing was low too...if i remeber correct about 184

Easy to make a monster out of th 250 crossers 🤪

Grüße Wolfgang

[Frits Overmars]

Why did the oems use cl8se to 2mm of squish on YZ250 and CR250?
reliability. accepts any fuel. even expiredI beg to differ. Less squish makes the engine less forgiving, not more.

[Wos]

Why did the oems use cl8se to 2mm of squish on YZ250 and CR250?


I beg to differ. Less squish makes the engine less forgiving, not more.

Frits,

Explain less forgiving ;) thanks


Do you mean the tolerances and reliability? Think with 1mm gap should be ok !?

Too my fellow, the engine was brutal...shot him directly on a overseas container nearby the cross track😯🙉

We continued with a fantic 125... yz motor😉✋

[Wos]

Frits,

Explain less forgiving ;) thanks


Do you mean the tolerances and reliability? Think with 1mm gap should be ok !?

Too my fellow, the engine was brutal...shot him directly on a overseas container nearby the cross track😯🙉

We continued with a fantic 125... yz motor😉✋

Frits!

I am thankful for all your given advice here...our teacher ;)

Question

How would you solve the beastyness of an 250 market given crosser?

Enlarge gap? Guess no!? ;)

Smoothen with ignition curve and reducing compression...
Another pipe?

And how would you create/ optimice a market given 250cross single ...as used by factory teams ....for a real pro Champion?😯🤪👍

Exiting Questions to me!

Thank you very very much!

Grüße Wolfgang

[wobbly]

I think we have a mix up in terminology.
First there is how forgiving the engine is mechanically , that speaks to how sensitive it is to the fuel/tune etc.
Having a squishband that effectively " doesn't work " by being too big , ie low MSV ,makes it more prone to detonation.
But on the other side of the coin , having aggressive squish velocity via high MSV makes it very sensitive on the throttle response ie harder to ride for a novice.

[jonny quest]

The YZ is a full on race bike. The CR is a full on race bike. The KTM SX is a full on race bike.

Makes no sense to me why the squish is so large. It's not manufacturing tolerance either. There is a reason they do it.... I haven't heard a good reason why.

[Frits Overmars]

Frits, Explain less forgiving thanks. Do you mean the tolerances and reliability? Think with 1mm gap should be ok !?With 'less forgiving' I meant: less tolerant of sub-optimal fuels, for example fuels that have been exposed to the outside air for a long time and have lost a large part of their volatile components. And also less tolerant of mixtures with sub-optimal fuel-air ratios, of sub-optimal ignition timings and of sub-optimal (i.e. high) engine temperatures.
1 mm squish gap should be OK for a 250cc MX single, as most of them have a 72 mm stroke. If it were my own bike, I would narrow the gap even further, to 1% of the stroke.


How would you solve the beastyness of an 250 market given crosser? Enlarge gap? Smoothen with ignition curve and reducing compression... Another pipe?I would not dream of enlarging the squish gap. I want the fastest combustion possible, which will permit me to ignite it late and so minimize any pressure rise before TDC.

Smoothening the ignition goes without saying: find the ignition timing curve that gives the best power curve, simple as that.

Reducing the compression ratio will make the bike more rider-friendly in most circumstances, and that includes road racing at Grand Prix level, as we learned when the factory Aprilias were compelled to switch from heavy-leaded fuel to no-lead fuel.

A different pipe? Absolutely. We (i.e. my friend Jan Schäffer and yours truly) performed a lot of tests and the best results came from pipes that practically 'castrated' the engine: several horses were gone missing. But throttle response became so much smoother that lap times improved, and the rider's condition was less strained during the course of the race. It proved a 'golden Griff ins Klo' as you Germans would call it, not just for kiddy bikes like the KTM 65SX, but also for top level riders.

EDIT: I see that Wobbly outbraked me. In my defense I can argue that it's two hours past midnight where I live while he's already had his first saturday morning coffee. Cheers Wob.

[husaberg]

Why did the oems use cl8se to 2mm of squish on YZ250 and CR250?

Parts variation. So if the worst combination of parts is used it will not hit anything.
i.e longest conrod rod with the shortest head and cylinder the lowest deck height crankcase and the tallest piston with the thinnest base and head gasket. You will not end up hitting the head when it's revved in anger.
That's why instead of the intended factory intended .9mm or whatever, you end up at 2mm or worse.
If you are racing a class where you have to use std parts or measurements. You use these tolerances to gain the best possible advantages or combinations.
Or you can normally modify them to gain the best of these acceptable tolerances.

example
https://www.kartengineshop.com/user/documents/upload/Homologation%2060cc%20Mini2.pdf
https://www.kartengineshop.com/user/documents/upload/Motori%20125cc%20%E2%80%93%20Omologazioni/Homologation%20125cc%20KZ10-C.pdf

These would be a good source of info if you say wanted to map and engine for one of the tunning programs.

[Wos]

With 'less forgiving' I meant: less tolerant of sub-optimal fuels, for example fuels that have been exposed to the outside air for a long time and have lost a large part of their volatile components. And also less tolerant of mixtures with sub-optimal fuel-air ratios, of sub-optimal ignition timings and of sub-optimal (i.e. high) engine temperatures.
1 mm squish gap should be OK for a 250cc MX single, as most of them have a 76 mm stroke. If it were my own bike, I would narrow the gap even further, to 1% of the stroke.

I would not dream of enlarging the squish gap. I want the fastest combustion possible, which will permit me to ignite it late and so minimize any pressure rise before TDC.

Smoothening the ignition goes without saying: find the ignition timing curve that gives the best power curve, simple as that.

Reducing the compression ratio will make the bike more rider-friendly in most circumstances, and that includes road racing at Grand Prix level, as we learned when the factory Aprilias were compelled to switch from heavy-leaded fuel to no-lead fuel.

A different pipe? Absolutely. We (i.e. my friend Jan Schäffer and yours truly) performed a lot of tests and the best results came from pipes that practically 'castrated' the engine: several horses were gone missing. But throttle response became so much smoother that lap times improved, and the rider's condition was less strained during the course of the race. It proved a 'golden Griff ins Klo' as you Germans would call it, not just for kiddy bikes like the KTM 65SX, but also for top level riders.

EDIT: I see that Wobbly outbraked me. In my defense I can argue that it's two hours past midnight where I live while he's already had his first saturday morning coffee. Cheers Wob.



Frits🙃

We dont outbreak us here on that superior forum... NO NO NO👍😂

many thanks to wobbly too...many thanks to you Frits for very detailed answers 👍👍😎

[Wos]

Parts variation. So if the worst combination of parts is used it will not hit anything.
i.e longest conrod rod with the shortest head and cylinder the lowest deck height crankcase and the tallest piston with the thinnest base and head gasket. You will not end up hitting the head when it's revved in anger.
That's why instead of the intended factory intended .9mm or whatever, you end up at 2mm or worse.
If you are racing a class where you have to use std parts or measurements. You use these tolerances to gain the best possible advantages or combinations.
Or you can normally modify them to gain the best of these acceptable tolerances.

example
https://www.kartengineshop.com/user/documents/upload/Homologation%2060cc%20Mini2.pdf
https://www.kartengineshop.com/user/documents/upload/Motori%20125cc%20%E2%80%93%20Omologazioni/Homologation%20125cc%20KZ10-C.pdf

These would be a good source of info if you say wanted to map and engine for one of the tunning programs.

I do not think this is the reason today, even when many parts and tolerances are involved.

For older days you may be right 😉

Diffrent bikes differ todoy only about 0,1 to 0,2 mm in serial gap these days...

Specially with undomed piston so so easy to measurue in production..to be save...

Grüße Wolfgang

[husaberg]

I do not think this is the reason today, even when many parts and tolerances are involved.

For older days you may be right ��

Diffrent bikes differ todoy only about 0,1 to 0,2 mm in serial gap these days...

Specially with undomed piston so so easy to measurue in production..to be save...

Grüße Wolfgang

Those 7 components plus stoke differences add to .8mm if its only .1mm per component.
The Japanese are masters and constructive laziness and only do stuff by hand using labour if it really matters to selling the product, measuring squish takes time if all the other manufacturers don't bother, thus they are all basically all hindered the same. So no potential gain for the additional labour inputs, so no real motivation to do it.
I cant remember exactly how but the Cranks gaps in mass-produced engines used to be measured with compressed air leakage rather than direct or indirect measurements or plastiguage or mics etc as it could be done in situ with air.
Honda C50 have 32 spokes as it was worked out it would save $1 a bike #note They have built 100 million of them.
Alloy frames used to be tig on the visible outside and mig in the bits you can't normally see.They don't always get stuff right, like not line boring cams in the 80's they thought their tight production tolerances would make it unnecessary as it had worked with cars.

[dutchpower]

125 sx 2023 ecu

Requested engine load

[Wos]

[QUOTE=husaberg;1131217587]Those 7 components plus stoke differences add to .8mm if its only .1mm per component.
[/QUOTE

Thanks for the Look inside japanese strategies 😯

I dont know the tolerances of japanese bike builders.

0.1 mm in japan? This is very huge? 😥

As a mechanic cant beliefe that husa✋

Should i better by a minarelli next...🤔

Grüße Wolfgang

[RomeuPT]

Hello

Does anybody know what is the standard thickness of vforce 2 reeds for CR 125? probably the same for other 125 motocross!?

I bought a replacement and it has 0.35, and the ones I had 0.4mm.

Not sure if I noted any difference in the power, no flutuation at high end and higher idle at least I felt.

Thanks

[koenich]

125 sx 2023 ecu

Requested engine load

Thanks Dutch! So which is the controlling factor to change injection mass flow?

[HSuomi]

Hello,

Decided to create account here as I have some problems with methanol and this forum has a lot of experience about it.

I have old air cooled Suzuki DS80 engine that im running with VP fuels M5 methanol. It works quite well and makes 12% more power than with 98 petrol. But problem is that after dyno- or top speed pull when you perss clutch it keeps reving insanely high for few seconds even the throttle is closed.
It must be killed with engine braking and brakes. Its even detonating after top speed test if clutch is pressed and needs a long engine braking. I've had bit similar problem with petrol but not even nearly so bad and it ends quickly.

Carb is chinese PWK 26mm with #32 idle jet and #220 main jet. Needle jet and needle are from bigger PWK. Needle is shortened to suit 26mm carb and randomly grinded with drill and sandpaper. It has electric fuel pump from K&N and needle valve flows 6,6dl/min. Engine has around 19whp with short dyno test.

What is the mechanism behind this behavior and any suggestions how to get rid of that?

Here is a little video, unfortunately first pull is missing where problem was worst. Second pull still has some and third for some reason is not so bad on this test. https://youtu.be/j8PJIAayKUU

[Pursang]

Carb is chinese PWK 26mm with #32 idle jet and #220 main jet. Needle jet and needle are from bigger PWK.
Needle is shortened to suit 26mm carb and randomly grinded with drill and sandpaper.

It has electric fuel pump from K&N and needle valve flows 6,6dl/min.

Electric fuel pump produces 4-7 psi. This is way more than the gravity head in a motorcycle fuel tank.

Perhaps the float valve is unable to resist inflow from flat out to suddenly zero. Fuel level rises and pilot system over delivers.

Rather than pressurise the carby, use the pump to feed a header tank with an overflow back to the pump supply.

[HSuomi]

Electric fuel pump produces 4-7 psi. This is way more than the gravity head in a motorcycle fuel tank.

Perhaps the float valve is unable to resist inflow from flat out to suddenly zero. Fuel level rises and pilot system over delivers.

Rather than pressurise the carby, use the pump to feed a header tank with an overflow back to the pump supply.

It has Y-branch and return line to fueltank with little flow restrictor. At least the carb is not overflowing.

[TZ350]

But problem is that after dyno- or top speed pull when you press clutch it keeps reving insanely high for few seconds even the throttle is closed.

What is the mechanism behind this behavior and any suggestions how to get rid of that?

"reeving insanely" is a very familiar problem for me with my two strokes and Methanol.

I think it is due to being a little lean or maybe being exactly on the correct Air/Fuel ratio and Methanol's predilection to auto ignition (which is different to detonation). 5-10% Acetone is said to reduce the tendency of Methanol to auto ignite. Auto ignition can induce detonation, so you can have patches in the rpm range where one or both are happening.

[wobbly]

I have two questions that may point to what is happening.
First , what is the actual float valve orifice size.
Second , if you are using a pump with a return and a jet restriction back to the tank , put a T in the fuel line next to the carb inlet , and run a clear fuel line upwards say 2M off this T.
Start the pump and rev up the engine.
What is the pressure height of the fuel in the clear line above the gasket face of the carb bowl , when the engine is reved.

[TZ350]

353540 353541 353542

Petrol Methanol setup. Remote Methanol chamber has a clear hose against the side of the carburetor float bowl so that the Meth fuel level can be seen and adjusted.

I am looking forward to trying this.

[dutchpower]

Thanks Dutch! So which is the controlling factor to change injection mass flow?

AFR and EGT

[diesel pig]

AFR? I know what EGT means I even have some gauges to measure it but AFR? and google is not helping.

[pete376403]

AFR? I know what EGT means I even have some gauges to measure it but AFR? and google is not helping.

air fuel ratio

[jonny quest]

Methanol post... did you try a surface gap plug?

[koenich]

AFR and EGT
I assume thats what you used to change the mapping!? I meant the OE setup, what is the Crank Pressure Sensor for and which factors will influence the injection?

[wobbly]

AFR = Lambda = LSU

[TZ350]

... what is the Crank Pressure Sensor for ...

Average crankcase pressure in a two stroke is much the same value whether you are making power or not.

The average crankcase pressure reading at idle is close to atmospheric and changes only slightly as the reeves head towards max torque.

I suspect the Crank Pressure Sensor might be being used for finding the "Difference" between "Max" and "Min" crankcase pressures during an engine cycle.

This "Difference" varies depending on the power output being developed and could be used as one of the factors for determining injection volume. Much like a MAP sensor on a four stroke.

4 stroke MAP - Lowest MAP pressure = 2 stroke smallest "Difference" .... 4 & 2 stroke engines idling.
4 stroke MAP - Higher MAP pressure = 2 stroke larger "Difference" .... 4 & 2 stroke engines making power.

The bigger the pressure "Difference" in a 2 stroke crankcase the greater the air flow and therefor injected volume required.

I would love to know more about how KTM actually use their pressure sensor on the EFI bikes.

[TZ350]

.

Pumper carburetors and pumper fuel pumps on a 2 stroke are activated by "Suck" and "Blow". "High" and "Low" crankcase pressure pulses.

The absolute pressure value of each individual "High" and "Low" pulse changes depending on the amount of power being produced.

But the "Average" value, ie ("High" plus "Low")/2 remains pretty much the same.

And the "Difference" value, ie ("High" minus "Low") changes according to the power being produced. More power, greater "Difference".

[dtenney]

Hello,




Decided to create account here as I have some problems with methanol and this forum has a lot of experience about it.

I have old air cooled Suzuki DS80 engine that im running with VP fuels M5 methanol. It works quite well and makes 12% more power than with 98 petrol. But problem is that after dyno- or top speed pull when you perss clutch it keeps reving insanely high for few seconds even the throttle is closed.
It must be killed with engine braking and brakes. Its even detonating after top speed test if clutch is pressed and needs a long engine braking. I've had bit similar problem with petrol but not even nearly so bad and it ends quickly.

Carb is chinese PWK 26mm with #32 idle jet and #220 main jet. Needle jet and needle are from bigger PWK. Needle is shortened to suit 26mm carb and randomly grinded with drill and sandpaper. It has electric fuel pump from K&N and needle valve flows 6,6dl/min. Engine has around 19whp with short dyno test.

What is the mechanism behind this behavior and any suggestions how to get rid of that?

Here is a little video, unfortunately first pull is missing where problem was worst. Second pull still has some and third for some reason is not so bad on this test. https://youtu.be/j8PJIAayKUU


We have dyno'd M5 as well and had the same problem with the lean condition likely because of the oxygenators used. The M1 works almost as well and is pure methanol and does not cause the lean condition. Thus we only use methanol without the added oxygenators.

[Condyn]

What is the thinking behind using multiple sheet metal thicknesses in one pipe? I faintly remember reading on here that Honda did that at some point, but have not figured out how to search effectively.

I notice when I have built a pipe out of thinner material it seems to light faster, and gets hotter to the touch much sooner. Does that also mean that the thin pipe also sheds heat faster than the thick one?

I short duration drag race AIR cooled snowmobiles which utilize a CVT, so rpm is maintained from about 5 feet from the launch to 500 feet. I purposely tune my clutches to allow some rpm increase down the track to follow the pipe as it heats. The pipe heat (open tipped fast response probe in belly) never stabilizes in 500 feet. The rate of temp increase slows, but it never plains out.

On the dyno, more warmup time pushes the peak power rpm further up in the rpm range. This comes as no surprise, but I did notice the power curve is overall lower with the rpm. VANNIK pointed out that this was likely due to the exhaust duct getting hotter and making the slug less dense. Makes sense.

The reason for my multi-thickness question is because I would like to heat the pipes on my warm up stand to my normal staging temperature as fast as possible and also give myself the best chance at keeping the duct as cool as possible. Would a thick header and thin rest of the pipe help this situation?

I have loads of belly temp datalogs with the thick pipes, and will be comparing to the thin ones once I build them in the next few weeks. I will share any interesting data I acquire.

[wobbly]

Answer to the question is the thin material heats quicker and cools quicker due to its inherent thermal inertia.
Honda and Yamaha Kit engines used 0.6 mm for the header and the last 1/2 of the rear cone ( in Ti of course ) with the rest of the body in 0.8.
Thus the 2 hottest parts of the pipe cooled quicker to improve acceleration after backing off into a corner , then heated up faster to give max top end on the straights.
Im completely unsure as to the use of this effect in a CVT situation , but would be interested in your findings.

[Vannik]

I short duration drag race AIR cooled snowmobiles which utilize a CVT, so rpm is maintained from about 5 feet from the launch to 500 feet. I purposely tune my clutches to allow some rpm increase down the track to follow the pipe as it heats. The pipe heat (open tipped fast response probe in belly) never stabilizes in 500 feet. The rate of temp increase slows, but it never plains out.

I have loads of belly temp datalogs with the thick pipes, and will be comparing to the thin ones once I build them in the next few weeks. I will share any interesting data I acquire.

Have you tried a 2-step approach like the 4T turbo engine guys do? They retard the timing and limit the rpm while staging to build turbo rpm but on a 2T you should be able to do the same to get the pipe to its optimum temperature. The moment they launch the timing goes back to optimum for power. If you could do this and use a thick walled pipe to get to and then stay at the optimum pipe temp maybe some gains?

[Condyn]

Wobbly I will be sure to share my findings. I am slowly learning how much influence real world field conditions layer on the variables.
Vannik, the 2 step idea has crossed my mind. It was always strictly forbidden in the classes I race in, however now I do not see it in the rule book. Might have to give that a try. Thank you both.

[HSuomi]

I have two questions that may point to what is happening.
First , what is the actual float valve orifice size.
Second , if you are using a pump with a return and a jet restriction back to the tank , put a T in the fuel line next to the carb inlet , and run a clear fuel line upwards say 2M off this T.
Start the pump and rev up the engine.
What is the pressure height of the fuel in the clear line above the gasket face of the carb bowl , when the engine is reved.

Float valva hole is drilled to 3mm.

I can test this next time when I do some other testings. Is the idea to find how much pressure the float valve is seeing?

There has been also comments about the oxygen/nitro in M5 methanol causing lean situation. But why is the engine running normal idle before the dyno/speed runs? What actually happens after the run to keep the rpm high? It goes normally back to idle when I rev it before the runs.

[wobbly]

Only other issue is that I have done a direct back to back with 1mm Vs 0.6mm pipes , and the thin wall pipe always makes more power on the dyno.
We cant do this in KZ as the pipe wall is spec at 0.8.

[Flettner]

Float valva hole is drilled to 3mm.

I can test this next time when I do some other testings. Is the idea to find how much pressure the float valve is seeing?

There has been also comments about the oxygen/nitro in M5 methanol causing lean situation. But why is the engine running normal idle before the dyno/speed runs? What actually happens after the run to keep the rpm high? It goes normally back to idle when I rev it before the runs.

Intetesting, with my 350 on E90, the tuning map required when the engine is cool is different to the map required when hot. It seemed that 70 / 80 degrees C is about the cut off. Above this needs about a 7 to 10% increase in master fuel. As it cools off it needs to go back to orginal fuel map again. Lucky the LINK ecu has a temp / fuel graph able to adjust according to temp.

Why? I guess above 70C the ethanol vaporises completely, under, not so. When ethanol vaporises completely I think thats when it releases more oxygen..... needing more fuel.
Im speculating, all I know is thats what my Kawasaki needs to run cleanly throughout its operational load variations.
It runs crank case EFI.

[Grumph]

I'd agree with those temps. Running a water cooled 4T on methanol my experience says use a 70C thermostat. Done just that on roadrace bikes, speedway cars and sidecars - and vintage race cars. One such with decades of poor running history cleaned out and ran better than ever with that change.

[Flettner]

I might add, trying to get the Kawasaki to run E90 through a carbutetor was pretty much impossible. Either too rich or too lean, set it for good power mid race and it would blubber for the first few laps or set it nice for the first few laps and have serious detonation after a lap or two.
EFI is the fix.

[Pursang]

I might add, trying to get the Kawasaki to run E90 through a carbutetor was pretty much impossible. Either too rich or too lean, set it for good power mid race and it would blubber for the first few laps or set it nice for the first few laps and have serious detonation after a lap or two.
EFI is the fix.

OK for Formula Libre .... tough for 'Historics'. Can we please have a simple analog thermal controlled main jet?

[Pagi]

353558

Woobly, Frits,

what do you think of the values?.......

[Grumph]

OK for Formula Libre .... tough for 'Historics'. Can we please have a simple analog thermal controlled main jet?

How about a separate slide for the air correction circuit - as Amal GP and TT and several other carbs.

Hugh Anderson reckoned to use the air control to get the small Suzukis up to temp and then stop them seizing once hot.

[Wos]

...like wobbly called it...are very delicious! 😉

To wobbly and frits...all others too ;)

I ve been aiming a MSV of min 33 m/s at peak power (10 000 or 11 000 rpm) in our classic enduros aircooled racers...and we definitely recogniced that we need less ignition timing and that there is a limit where we gain no more power by ignition...

Is there a rule of thump if we improve the MSV further ...within the " rule of thump 1 % squish ".... to how much we can set ignition later?

Were we need less ignition timing?

Think if begin resonance is working earlier with high MSV .. . we can/ should reduce ignition timing earlier...

And after reaching resonance area???

Think MSV influence on ignition point getting smaller because we have better fuel charge?

Next free lunch please! ;)

Thanks and Grüße!!!

Wolfgang

ps frits !

...jan schäffer is well known in germany..top ...not my direct friend...but i am impressed by his sucesses in simpson or liedolsheim races were we took part 20 years ago with Kreidler 😀

[wobbly]

A BiMetalic strip on the head opening and closing a tube connected to the air corrector inlet would be accurate and analogue

[wobbly]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

[Wos]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

Hey wobbly,

Tanks to you at nearly midnight here! 😉

Start point at 38 m/s at which rpm?

Power incerease realy?? This would be wooow!? 😀

Excuse my question... 😉 if i am right...that was never carified in special context here.. but very interesting point...😀 for a hobby 2 stroke addicted like me

Merci! ;)

[Wos]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

Like ktm, yamaha and so on do today???

With a bevel 12 degree on pistons upper edge???

Dosnt that trap end gases in squish gap!?
Provocate detos?

Arnt they completely wrong? 🙃🤔

Only commercial thing of easier produdction???


Confused as i am!! ✋🤔🙃

[wobbly]

The squish band in the head should always be colinear with the piston , be it flat . radiused or conical, and as small a vertical clearance as is mechanically viable.
I can only give definitive guidance over what has been done in KZ racing over the last 4 homologation periods , that is 3+3+3+4 years.
initially there was domed with a bore tangent of 12* - next was a conical piston with a 7* rise , this was accompanied by higher axial transfer roof angles.
Then a 4* conic , again with increased transfer axial , lastly they used my design with a 4* conic changing to a 50% area flat top.
The last change was worth 0.5 to 1.5 Hp back to back on the same transfers.
A flat top looses around 1 Hp back to back against the latest setup, having to use a part spherical chamber design.

BUT , I have done testing previously where combustion volume and shape isnt limited ( 125 MX engines ) , and a flat top with a proper toroid shape , and more transfer axial is easily the best.
This shape has the least piston heat soak area , pulls the spark gap into the middle of the chamber , and also puts the initial expanding combustion bubble right in the firing line of the
turbulent eddies off the squishband edge , creating faster burn speed across the chamber.
This is analogous to advancing the ignition timing without the downside of pumping losses due to extra compression force when approaching TDC, after the gap has been ionized.
I would use this in a heartbeat for KZ , but the heads outer toroid shape traps air when cc checking per the rule book.

From all the testing I have done my setup of choice would be the flat top , with a piston edge radius , omitting the radius over the boost port or even better lifting the boost port floor well
above BDC to stop flow attaching to the radius and pulling it down toward the Exhaust exit , increasing short circuiting and ruining the scavenging pattern.

[Frits Overmars]

Woobly, Frits, what do you think of the values?Acording to the port shape concept below the minimum safe vertical half-axis for a 74% wide elliptical port should be 17,7 % oif the cylinder bore.
Converting this ellipse to a multi-radius port (with the ELLIPSE program that you can find in my FOS software) gives corner radii of 11,4 % and a center radius of 67 % of the bore.
So your 12% corner radii are OK Pagi, but your 210 % top center radius is far too flat (your 50 % bottom center radius is OK though).
353559
By the way, a 74% wide port with safe radii is no better than a 70% wide port that can have a larger center radius and smaller corner radii, offering more flow area on top, where it counts, because that is the area that is open for the longest time.

[Frits Overmars]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.For me, Maximum Squish Velocities are not even a guide. Like Wobbly I prefer to make the squish gap as tight as is mechanically possible. I have never yet seen an MSV calculator that takes the dynamic stretch of a high-revving engine (about 1% of the stroke) into acoount and as a consequence their quoted MSV values make no sense at all.
Below you'll find a comparison of MSV values for the Aprilia RSA.
Without taking dynamic stretch into account the MSV would be 63,95 m/s. With 1% dynamic stretch the MSV appears to be 144,21 m/s. Some difference, isn't it?
353560 353561

[Pursang]

A BiMetalic strip on the head opening and closing a tube connected to the air corrector inlet would be accurate and analogue

Thanks wobbly, for that idea.

Carburetted Toyota's used lots of these for vacuum switching in various emissions control systems :
https://lzd-img-global.slatic.net/g/p/c6b4fc14f9d1f8f4da5268a52b6f62d5.jpg_720x720q80.jp g

Different models/colours probably have different opening temps. One schematic I found said it was opening at 104 deg F. (40 C.)

Yamaha used this one in outboards:
https://images.cmsnl.com/img/products/valvebimetal-vacuum-switch_medium6G81439900-01_769e.jpg

Still Looking for an adjustable one (or one operating around 70C.)

[Wos]

Thank you wobbly 👍

"lastly they used my design with a 4* conic changing to a 50% area flat top"

Thats exactly what we do with flat top pistons from yz 125 yamaha or ktm with a steep bevel 12 degree of the piston axis...!!!!

Instead frontal colliding squish that partly eleminates energy
idea was to gain a force/ direction upwards to spark plug when squish is colliding in the middle of piston...

Little bit like frits concept with a domed one...

Second reason was to avoid a trap in squish, which the 12 degrees bevel without having its conterpart in head is!

Yes in stock there is a trap 🙃

3. Hard to do and proof the bevel in head beeing flush and parallel to piston

4. There has to be an energy loss / MSV loss with an angel of 78* in squish gap... 🤔



The yamaha has very steep a (35 degree) and b ports ( 25)

Ktm year 17 a is under 20 degree

Grüße! Wolfgang

[Pursang]

Bit more info on bimetal vacuum valves from a 4WD forum:

90925-05035 (violet) opens at 44°C (111°F) and closes at 30°C (86°F)
90925-05046 (pink) opens at 19°C (66°F) and closes at 5°C (41°F)

90925-05035 controls EGR, Primary Vacuum Advance and Evap.
90925-05046 controls the Choke Opener System.

90925-05047 (blue) was used in a broad range of applications from Corollas to 4-Runners, ~ ’87 – 94.
Picking one at random, it was used for the EGR systems on the 1988 MR2.
The FSM for that car states that the valve should open at 54°C (129°F) and close at 35°C (95°F).

https://forum.ih8mud.com/attachments/90925-05046-jpg.1519364/

[Flettner]

Nah, just run a disc valve motor, that way you can run efi without anyone anyone knowing. 😁

[Wos]

For me, Maximum Squish Velocities are not even a guide. Like Wobbly I prefer to make the squish gap as tight as is mechanically possible. I have never yet seen an MSV calculator that takes the dynamic stretch of a high-revving engine (about 1% of the stroke) into acoount and as a consequence their quoted MSV values make no sense at all.
Below you'll find a comparison of MSV values for the Aprilia RSA.
Without taking dynamic stretch into account the MSV would be 63,95 m/s. With 1% dynamic stretch the MSV appears to be 144,21 m/s. Some difference, isn't it?
353560 353561

Tanks Frits,

One of best things in life...are Kisses😛🥰... when piston kisses head...slighty an smooth😋👍😎

If i am right, rsa had 0,7 mm squish!?

This is more than 1%?

Reason?

Dont know the stretch of all involved parts at the yz 125 at 13000 in overrev... 0,7 works...no marks on piston... mayby next 0,65...

The only way to find minimum gap... seens to risk piston kissing head??? 😉🥰 ...😅🤣

Other ideas???


Tanks meister! ;)

Grüße at all!


Wolfgang

[wobbly]

TM KZ engine with 0.82 squish will kiss the head at 15500 , we rev them to 14800 all day.
In this application 0.82 is a little wider than mechanically possible , but any less and i have to retard the spark more to keep the overev, but this ruins the front side power. NFG,
I have just finished doing a rod model in SolidWorks and now have the rod inertia force ( less the combustion pressure ) at TDC
from Thomas Johansson so will do an FEA for the predicted rod stretch tonight.

[Frits Overmars]

TM KZ engine with 0.82 squish will kiss the head at 15500 , we rev them to 14800 all day.
In this application 0.82 is a little wider than mechanically possible , but any less and i have to retard the spark more to keep the overev, but this ruins the front side power. NFG,
I have just finished doing a rod model in SolidWorks and now have the rod inertia force ( less the combustion pressure ) at TDC
from Thomas Johansson so will do an FEA for the predicted rod stretch tonight.You are punished by the rulebook that won't let you use a variable ignition timing.
Wob, it's too late in the day for me to do the math, but my gut feeling tells me rod stretch is not the main factor in dynamic stretch. I suspect crankshaft bending is the number one culprit.
Yeah I know, I keep telling everybody else that gut feeling should not enter the equasion :whistle:

[wobbly]

Well said Frits , I have all the nominal bearing clearances , so I can add these to the rod stretch , and see how much extra
dynamic elongation can be attributed to the crank ( big end and small end pin bending I can add into the FEA analysis as well ).

[Wos]

Wobbly and Frits,

Nearby all calculations or simulations 😉...that i am not able to do..


Heard about seeing the touch of piston in builded up coal on piston surface...

Idea is to add /Find to add... a material for surface piston, that keeps footprint of head to measure, evaluate Real gap at highest rev...without doing damages anyway...that we as a non pro could not afford😥

Mayby kind of spray paint...or what ever ;)

Ideas welcome! 😉

Wolfgang

[jamathi]

Tanks Frits,

One of best things in life...are Kisses����... when piston kisses head...slighty an smooth������

If i am right, rsa had 0,7 mm squish!?

This is more than 1%?

Reason?

Dont know the stretch of all involved parts at the yz 125 at 13000 in overrev... 0,7 works...no marks on piston... mayby next 0,65...

The only way to find minimum gap... seens to risk piston kissing head??? ���� ...����

Other ideas???


Tanks meister! ;)

Grüße at all!


Wolfgang

The RSA piston did not touch the head with 0.4 squish.
It gave much more power until 12000, but would not rev whatever we did..

[Wos]

The RSA piston did not touch the head with 0.4 squish.
It gave much more power until 12000, but would not rev whatever we did..

Hey jan!✋👍

Wow 0,4 mm...thats a really strong rod and crank😎😲

Mayby squish has "blown out" spark...?

On the other hand...i am quiet sure you had best available ignition system

Whatever...kongratiolations to your sucesses!! 😉

Grüße Wolfgang

[wobbly]

I am guessing that under full load on the dyno the combustion pressure pushing on the piston would negate the bearing clearances and some of either rod
stretch and or crank flex. I think on the overun into a corner , with no throttle it would be sudden death.

[ken seeber]

Way, way back in those heady Ryger days (2015 = 8 years ago...time flies hey?) I did a calc of the net piston forces.
The main inputs being piston acceleration, its mass and the opposing forces provided by a known cylinder pressure trace.

The attached shows these net forces at various rpms.

Please don't ask me if these are accurate though.


353567

[husaberg]

i was reading something about a tuned Ducati it went along the lines as when they reset the squish the power went up.. but also the Decibel's went down. I can understand the hp but with the Db's
Is it due to more complete or faster combustion? Do we have a physicist...;)

[jato]

Time flies alright! re crank flex about 20 years back i did the calcs for a short stroke (64mm) rm250 and (from memory) at 12000 rpm there was something like 11000 N of reciprocating inertia, diluted with 50% balance factor leaving the equivalent of a bit over half a ton of load carried by the main bearings. Ignoring combustion pressure to allow for upshifting and closing the throttle i then set up the rm crank supported by the bearing journals and carefully applied 550 kg to the crank pin... i can't remember the value now but the crank flexed steadily as the load was brought up to what it would see in service - possibly something like 0.2 mm (or more) at the middle of the rotor's taper

[Wos]

I am guessing that under full load on the dyno the combustion pressure pushing on the piston would negate the bearing clearances and some of either rod
stretch and or crank flex. I think on the overun into a corner , with no throttle it would be sudden death.

Longer time in my mind...

The squish gap in a kind of air cushion...the closer the more damping...

And maybe this has influence of the tilt of piston at tdc...

Clarify me if wrong! 😉

Thanks!

Wolfgang

[Frits Overmars]

i was reading something about a tuned Ducati it went along the lines as when they reset the squish the power went up.. but also the Decibel's went down. I can understand the hp but with the Db's. Is it due to more complete or faster combustion? Do we have a physicist...;)We do. More effective squish = faster combustion = more time between end of combustion and initial exhaust opening = longer expansion phase = more combustion gas energy used for piston movement = less combustion gas energy left for noise.

[philou]

The RSA piston did not touch the head with 0.4 squish.
It gave much more power until 12000, but would not rev whatever we did..

do you have any idea of the power in millijoules of the ignition of the aprilia?

[jonny quest]

Polini had a variable combustion chamber... when cylinder pressure overcame pressure in cylinder head dome, it moved lowering compression.

I had read Yamaha had tried this as well. Why didn't it catch on?

[husaberg]

We do. More effective squish = faster combustion = more time between end of combustion and initial exhaust opening = longer expansion phase = more combustion gas energy used for piston movement = less combustion gas energy left for noise.

Thanks Frits

314930314931314932

What is this head ... could it be a variable compression head????? Help Please.


Polini had a variable combustion chamber... when cylinder pressure overcame pressure in cylinder head dome, it moved lowering compression.

I had read Yamaha had tried this as well. Why didn't it catch on?
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130892885#post1130892885

[Peljhan]

As we are speaking about heads and squish etc. I have a riddle here and maybe you guys have some ideas before I get into it.

In 2021 I made a new chamber for my Tomos D6 [50cc watercooled, bridged exhaust 195°, two stransfers 128°, piston port, PVL kart ignition]

New head has better cooling and more structural rigidity but it lost power drastically. Dimensions should be same as with old head, except squish went from old 0,55mm to new 0,48mm (will measure both heads again in future).
You can see black graph was best power a year earlier and there was no driving between tests. Red graph is new head and I never saw so much power lost and I made lot of modifications over years.
Another mod made in same time was repositioning of EGT probe (5mm thick stack gauge probe) from about 250mm exhaust length measured from piston to about 120mm length. I tought this was the case for low power but with removing a probe there was not much difference - blue graph.

353568353569353570

[wobbly]

Without making a comment on the actual effect of changes , what's going on with the weather correction for this software.
You have the difference between 19 to 25*C air temp and 0 to 60% humidity.
0 cant be correct , but is the air being corrected properly ?

[Peljhan]

Uh, I think I forgot to input weather data (correction factor) for red curve :facepalm:
Can't do it now, only when measuring. It is cheap software.

[wobbly]

Do you have a choice of Correction.

[41juergen]

@Wob: you mentioned some when that the distance of the spark plug tip to the piston shall be approx. 6 mm as shown in my sketch... is that valid for flat pistons as well for domed once or a setup with a straight angle/ flat dome?

[wobbly]

For a flat top I have been as close as 3.5mm , but only because the chamber was very small for Methanol.

[lodgernz]

For a flat top I have been as close as 3.5mm , but only because the chamber was very small for Methanol.

I always try to position the plug gap at the point where straight lines from the squish band meet.
Is that wrong?

[wobbly]

That works just fine for a dome , but of course cant be done with a flat top.
In that case its just a matter of juggling the toroid chamber shape and the spark gap position.
I dont know how much is too much as Ive never had a chance to test it properly , but I believe you can get the toroid roof too high , ie the plug boss down very low, and that this geometry may
affect the scavenging loop arriving from near the rear wall and travelling across the chamber.

[Peljhan]

Do you have a choice of Correction.

No, I can't even export it in excel or something else.
If we use only corrected blue and black curve, there is still missing complete power top on blue curve with new insert.

[dtenney]

Looking for a bit of help, please. Is there a standard or a formula for calculating the needed distance from the piston crown to the spark plug? This is for a square bore/stroke 85cc motor.

[Peljhan]

Looking for a bit of help, please. Is there a standard or a formula for calculating the needed distance from the piston crown to the spark plug? This is for a square bore/stroke 85cc motor.

I doubt you will find a formula for that. I had a gap lower than 1,5mm on 90cc (18hp) "square" aircooled engine. I was experimenting with head inserts and needed to put a 1,5mm shim under sparkplug in one instance to get more clearance. When I forgot to install a shim once, piston tuched the plug and engine didn't start. It was working fine with about 1,5mm gap, the only difference I saw was clear spot at the center of piston dome, but no detonations visible.

[jonny quest]

Thanks Frits



https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130892885#post1130892885


Good catch Husa! No one had any information back then either!

[wobbly]

Peljhan , the factors in play to kill top end are MSV , that obviously has changed dramatically with the closing up of the clearance, compression , that should be the same cc
or finally maybe the head was deforming previously - as you said the new one was alot stronger.
In any case the instant result of any factor like this is a big drop in EGT - so you need to start logging this , as to get a real correlation between any two setups you should
be adjusting the jetting to hit a target egt number..
The fix is a reduction in ignition timing , past the point where the power graphs cross.

Re the plug position , the pointers for this exist in Jan finding that a flat roof " bathtub " chamber gave better power over a simple part spherical shape, that pulls the plug gap down closer to the piston.
Then we have the toroidal shape , that pulls the plug down even further , and testing I did showed this was absolutely the best for a flat top piston.
The only other factor as mentioned before was my feeling that having a very deep toroid roof , with a large plug boss intruding into the combustion space , may ideologically seem good for flame front positioning
but could in fact start to disrupt the scavenging loop flow.

[41juergen]

Thank's a lot for all the feedback!

[Wos]

Very very interesting Diskussion... answers about head, flat top, domed, distance plug...squish and the special influences😎 wow...😲

My next question

the angle of squish band to the head shape ending to ...for example " bathtube"...


Which is optimum " crossing" angle of both geometric " flow directions"?

Crossing 90 degree?... thats what i do🤔

or with flow from head in direction of squish?...angainst it🤔✋

Thanks for continuing exiting answers✌🥰

Wolfgang

[wobbly]

In my dyno testing of heads for a flat top piston I tried three geometries of chamber outer wall with the toroidal shape.
Each was optimized for ignition timing and best power egt.
First was a wall at the bowl edge of 90* that then formed a radius into the toroid roof shape.
This needed less ignition and a bigger jet , compared to the original flat roof semi tophat shape - background detonation level was considerably less , and power was up the front side nearly 0.5 Hp and around 1.5 Hp in overev.

Next was a radius all the way to the bowl edge that was 30* from vertical at the intersection.
This needed the same setup as above but made around 0.3 to 0.5 Hp more everywhere.

Last was a straight wall @ 60* up from horizontal , then forming the toroid roof radius - so the radiused roof was higher to achieve the same cc
This needed more ignition , and a smaller jet , but the power was much the same as the tophat example.

Squish and cc were all identical and had no radius on the squish/bowl edge , just the sharp corner broken with wet and dry.
I wish i now had the opportunity to try chamber shapes with the latest piston , having a conical squish , transitioning into a flat top with 50% bore area.
This is the shape I used in the BSL 500 , but only with a bathtub , as that is what Jan had found worked best at the time.

[Haufen]

So 90° was the best, followed by 60° and then 30°?
And the original was a flat roof bathtub style but with edges in the corners (tophat) instead of radiuses? Is that correct?

[wobbly]

No , the 30* tangent intersection with full radius all the way up into the toroid was best , it made a little more power than the 90* version - ie no vertical flat section before the toroid roof radius.
Sorry that wasnt clear the way I described it.
So , 30* , 90* then 60* = same as tophat ( but this toroid also had less background deto like the others over the tophat design ).
All tests had no corner rad at the bowl edge including the tophat.

[Gradella23]

No , the 30* tangent intersection with full radius all the way up into the toroid was best , it made a little more power than the 90* version - ie no vertical flat section before the toroid roof radius.
Sorry that wasnt clear the way I described it.
So , 30* , 90* then 60* = same as tophat ( but this toroid also had less background deto like the others over the tophat design ).
All tests had no corner rad at the bowl edge including the tophat.


thanks for the insight, may i ask you to post a pic or a sketch of a toroid chamber to understand what dimensions are you higlighting?
probably it's an english language understanding problem, i'm sorry for this... you can maybe draw them on the blue toroid prototype you posted some years ago

thanks again

[lohring]

This has been posted in the past.

Lohring Miller

353590

[Gradella23]

This has been posted in the past.

Lohring Miller

353590

Thanks Lohring. So i guess this is similar to the 30° version (30-7,5°?)
I'll obtain something like this: i can't find enough volume compared to the standard shape, even if I reduce a lot the squish band. (40mm bore, 0.45mm squish, something around 16:1). Am i missing something?

[wobbly]

What chamber cc are you shooting for - I will do a CAD sketch for you - maybe this setup would be best with a small thread plug.

[wobbly]

So I looked thru my files and found a TZ50 , this is 40 bore with 39.3 stroke.
With 16:1 the cc is 3.33 and squish is 0.42 and to get 38M/s MSV the width is 50% = 5.84mm
This uses a 10mm NGK race plug with Iridium fine wire electrode and a Platinum fine wire ground = R0373A - 10 the same nose configuration as the 14mm R 7376 that is the best
race plug in every other configuration.
As this isnt a flat top the chamber wall can be steeper to suit as the squish is also angled.

[Frits Overmars]

353596
Wob, I noticed that your suish area radius = piston dome radius + squish gap. But in a running engine most of that squish gap disappears, which causes an (admittedly, miniscule) occluded volume at the outer edge of the squish area. Therefore I prefer to make the squish area radius equal to the piston dome radius.

[Vannik]

Frits, something just for you!

https://www.youtube.com/watch?v=M92nNsxe7W8

[Wos]

...so awsome listen to you experts 👍😯

[Frits Overmars]

Frits, something just for you!
https://www.youtube.com/watch?v=M92nNsxe7W8A 700cc four-cylinder two-stroke on methanol without any form of supercharging except for the contribution of the pipe, putting out in excess of 350 Hp?
That's over 0,5 Hp per cc. That would be damn good from a 50cc single. But from a 700-4?? 'If something sounds too good to be true....'

[Wos]

Have my daughts too frits.
Too much friction in 750cc engine

A kreidler made 440 hp per liter in the 80ties

Aprilia Rsa 432 hp/ l

Best 50 cc today frits ?
Best prooven hp/ liter ever?

I ve heared about slightly over 26 hp on 50cc....ergo 520 hp/ liter...can that be true? 😉

Apropos... feavering for liedolsheim/ germany... 50cc 8H endurance Race in September 👍👍😲😎🥰

Wolfgang

[Frank S.]

Apropos... feavering for liedolsheim/ germany... 50cc 8H endurance Race in September 👍👍😲😎🥰

Wolfgang[/QUOTE]

I will be there :Punk:
Who else?

[wobbly]

Frits, if you are thinking of the piston/head geometry changing , then we should be addressing the rock over at TDC as well.
And if we estimate an added 15% power due to Methanol then the RSA would be 506 Hp/L as a benchmark.
Thus the 700 is making very close to the same power per L , to me the pipes dont look clever enough to do this on a reed engine with 175cc cylinders.
But they will be measuring power at the crank , the RSA was at the sprocket , so a variation there in favor of the 700.

[TZ350]

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[Niels Abildgaard]

Have my daughts too frits.
Too much friction in 750cc engine

A kreidler made 440 hp per liter in the 80ties

Aprilia Rsa 432 hp/ l

Best 50 cc today frits ?
Best prooven hp/ liter ever?

I ve heared about slightly over 26 hp on 50cc....ergo 520 hp/ liter...can that be true? 😉

Apropos... feavering for liedolsheim/ germany... 50cc 8H endurance Race in September 👍👍😲😎🥰

Wolfgang

Power per ccm is for amateurs.
The iron power limit is blowdown time area and I started to explain it here in post 34362

[Mike Fisher]

Robby Galletta also mentioned "nitro and other good stuff" or words to that effect. I looked at a few of his YouTiube clips, so the reference to nitro might not have been in the first one that Vannik flagged up

[Wos]

Robby Galletta also mentioned "nitro and other good stuff" or words to that effect. I looked at a few of his YouTiube clips, so the reference to nitro might not have been in the first one that Vannik flagged up

I was talking about pump gas like used in gp even when in the 80 there were leaded pump fuels 😉

Todays i am in liedolsheim only as a spectator and to smell 2 strokes🥰🤣

Grüße Wolfgang

[Wos]

Apropos... feavering for liedolsheim/ germany... 50cc 8H endurance Race in September 👍👍😲😎🥰

Wolfgang

I will be there :Punk:
Who else?[/QUOTE]

Hey frank

Are you frank schäfer from team 39 lucky Losers? Rider in liedolsheim and porsche mechanik/ engineer...? 😀

Having colleague peter k. from diefenbach?

You will remember my face, when we meet again

But maybe lets talk bevore the race to exchange ideas while drinking a 🍻

Grüße aus Sternenfels ✋😉

Wolfgang

[TZ350]

Power per ccm is for amateurs.

Agreed, but I thought BMEP, break mean effective pressure was the yard stick by which you could compare internal combustion engines, even engines of different types and configurations.

[Peljhan]

Peljhan , the factors in play to kill top end are MSV , that obviously has changed dramatically with the closing up of the clearance, compression , that should be the same cc
or finally maybe the head was deforming previously - as you said the new one was alot stronger.
In any case the instant result of any factor like this is a big drop in EGT - so you need to start logging this , as to get a real correlation between any two setups you should
be adjusting the jetting to hit a target egt number..
The fix is a reduction in ignition timing , past the point where the power graphs cross.


Thanks. Will dismantle it over winter and do exact measurements. Will also try to fit the old head back and do testing again.
I got open tip egt sensors you suggested, but my dyno has no option to plug them. I must get some kind of data logger. May I ask what sampling rate you use for your EGT?
For now I have only stack EGT gauge with closed tip, do you think I can change only probe on this gauge?
And I was reading somewhere, that sensors need to be correctly plugged/soldered to measure correctly but I can't find info anymore, I think I got it somewhere on egt page.

[lohring]

We tested our 26 & 35 cc race engines with a Performance Trends data logger and their dyno software. Today their data logger is more compact and has a weather station. https://www.performancetrends.com/dtm-dyno.htm Below is an article on our dyno. A more modern version has been built by Mark Anderson to continue testing our small race engines and pipes.

Lohring Miller

353597

[Niels Abildgaard]

Agreed, but I thought BMEP, break mean effective pressure was the yard stick by which you could compare internal combustion engines, even engines of different types and configurations.

For a first sketch of a super two stroke cylinder one can do worse than scaling a RSA.
54 horsepower from 125ccm and had cost a zillion to devellop.
54 has not been bettered in the meantime.
If we go for a 250ccm cylinder by multiplying all lengths dimensions by cuberoot of 2 (1.26) the blowdown-timearea becomes 1.59 times bigger and therefore max power can be tuned to 86 horsepower with clever people and money enough..
A 50 cubic cylinder as clever as RSA with tuned exhaust can by the same method be calculated to have a max power potential of 29 horsepower and a 26ccm ca 19 horsepower

[wobbly]

Peljhan , the Stack is way too slow , hasnt got max recall , and the enclosed tip type probe will never keep up with a racing 2Ts temp delta.
My software samples the egt up to 100X / sec and needs minimal smoothing , but I tried 10X and the result was all but identical.
Plus the Stinger exposed tip probe is real fast and importantly can be located on the header centerline.

You need the speed , and more importantly , having a graphed output , showing when a leaner jet change does not achieve a consistent temp rise - this shows you instantly deto is starting
due to rising free radical formation under the ring is robbing heat energy , and gives you a direct indication of best power egt level.

I also have 0-5V deto level being logged , but as the egt stops me from being dumb and getting into enough deto to hurt a piston , its now pretty much redundant information.
Except for seeing when say a pipe or head modification reduces the background deto level , that subsequently can give more leeway to lean on an engine to extract more performance.
This is what I like about toroidal chambers.

There is also a Lambda if I want , but I found that although it accurately shows what the oxygen level is in the exhaust gas , this metrics scaling doesn't change significantly enough as you
hone in real close to your best tune.

[Frank S.]

Wolfgang
You got me...:drinknsin

Grüße aus Göbrichen

[yatasaki]

Apropos... feavering for liedolsheim/ germany... 50cc 8H endurance Race in September ����������

Wolfgang


I will be there :Punk:
Who else?[/QUOTE]
We go for 24h endurance in Serbia beg. of october.
Aircooled only

[Wos]

Wolfgang
You got me...:drinknsin

Grüße aus Göbrichen[/QUOTE]

Sended a pm to you...

[wobbly]

Wos , the unleaded FIM GP fuel brought into being in 1998 was nominally 100 octane , but was so dangerous to handle gloves and a respirator had to be used to fill the tanks.
Teams also refrigerated it prior to use.
Elf did a ton of research on the mix , ending up with what was called MITS 32 that would literally melt your nose.
So much for the virtue signaling clean green bullshit.

[husaberg]

Wos , the unleaded FIM fuel brought into being in 1988 was nominally 100 octane , but was so dangerous to handle gloves and a respirator had to be used to fill the tanks.
Teams also refrigerated it prior to use.
Elf did a ton of research on the mix , ending up with what was called MITS 32 that would literally melt your nose.
So much for the virtue signaling clean green bullshit.

I assumed they did this as by refrigerating it they can have more fuel for the same volume ie increased density (until it warms up anyway.) in the same size tank

[Niels Abildgaard]

Hello Wobbly

In dec 2020 You were engaged to do some 30.5ccm experiments.
Can You tell what You achieved?

[Flettner]

I assumed they did this as by refrigerating it they can have more fuel for the same volume until it warms up anyway.

Suzuki used to do this in the Castrol six hour races, at Manfield.

[Wos]

Wos , the unleaded FIM GP fuel brought into being in 1998 was nominally 100 octane , but was so dangerous to handle gloves and a respirator had to be used to fill the tanks.
Teams also refrigerated it prior to use.
Elf did a ton of research on the mix , ending up with what was called MITS 32 that would literally melt your nose.
So much for the virtue signaling clean green bullshit.

Thanks wob👍

If you look closer behind ...most green things are totally bullshit🤮

[wobbly]

Hello Niels , I had to sign an NDA for that project , but suffice to say I changed absolutely everything including all the port radial and axial directions , used a longer rod , and did a Titanium pipe.
I would have to go back and see what the NDA terms were , but its was the usual story of not enough funds nor enough fundamental knowledge of leading edge
2T technology by the guy I worked with.

The frozen fuel in GP racing was more about being faster for 5 laps , as the volume change due to the temp delta was minimal.

[husaberg]

Suzuki used to do this in the Castrol six hour races, at Manfield.

I had heard of aussies pre prepping the tank by freezing the tank whist full of fluid to increase the total capacity when the water expanded.....it was still stock just a bit mishappened...

[Niels Abildgaard]

Hello Niels , I had to sign an NDA for that project , but suffice to say I changed absolutely everything including all the port radial and axial directions , used a longer rod , and did a Titanium pipe.
I would have to go back and see what the NDA terms were , but its was the usual story of not enough funds

Thank You for answering.

It is just a game to see if someone can better the Aprilia RSA perfection.

Formula is

(30.5/125) ** 2/3 multiplied with the imortal 54 horsepower and that means 21.o8 horsepower for the 30.5 ccm as the choking limit of the optimum blow down time area.

[Frits Overmars]

It is just a game to see if someone can better the Aprilia RSA perfection.
Formula is
(30.5/125) ** 2/3 multiplied with the imortal 54 horsepower and that means 21.o8 horsepower for the 30.5 ccm as the choking limit of the optimum blow down time area.Niels, predicting the achievable engine power via the cube root of (its cylinder capacity divided by the cylinder capacity of the RSA) is mathematically correct, but physically only applicable when those cylinder capacities are not too different from each other.
An elephant is never cold and a mouse is always shivering: relative heat losses increase strongly with small cylinder capacities because the surface/volume ratios increase sharply. And a second rescaling problem is that boundary layer thicknesses are not scalable.

[SwePatrick]

A 700cc four-cylinder two-stroke on methanol without any form of supercharging except for the contribution of the pipe, putting out in excess of 350 Hp?
That's over 0,5 Hp per cc. That would be damn good from a 50cc single. But from a 700-4?? 'If something sounds too good to be true....'

That what a well tuned methanol engine do..
i know of a similar engine in sweden, only 500cc thou, but it puts out 261hp
And remind yourself, they measure power differently.(not on the sprocket)
Normal powergain on methanol on a twostroke watercooled engine is in the area of 8-11%

[lohring]

We've been running very small engines on nitro/methanol fuels for a very long time. Inertial dyno tests on these engines have also been done for a long time and continue today. A sample of some early testing is in this paper. https://web.archive.org/web/20030205134346/http:/rcboat.com:80/dyno.htm It shows a BMEP of 92 (6.3 bar) and 4.44 hp at 20,000 rpm in an 11 cc engine. They were running 65% nitro and i bet around 20% oil. I doubt that any of these engines exceed a BMEP of 100 psi (6.9 bar).

We ran a lot of similar tests on 26 cc gasoline fueled engines and race boats. We also did some fuel testing on an engine setup for gasoline to see how fuel cheating would work. We decided that it wouldn't matter unless the engines and pipes were designed for the methanol fuels.

Lohring Miller

353600

[Gradella23]

So I looked thru my files and found a TZ50 , this is 40 bore with 39.3 stroke.
With 16:1 the cc is 3.33 and squish is 0.42 and to get 38M/s MSV the width is 50% = 5.84mm
This uses a 10mm NGK race plug with Iridium fine wire electrode and a Platinum fine wire ground = R0373A - 10 the same nose configuration as the 14mm R 7376 that is the best
race plug in every other configuration.
As this isnt a flat top the chamber wall can be steeper to suit as the squish is also angled.
Thanks Wobbly, mine is 40x39,7 but i got the concept. It's almost impossibile to teach this configuration without an M10 plug, that was the main issue. I'll try boh solutions and see what happens. Have you experienced significant gain using a domed sqhish band with the same radius of the piston versus a tangent -best similar angle One? The difference in height would be only some hundreth of mm

[wobbly]

Never been able to back to back test a very close tangent squish against a radiused squish as I always use CNC for this where I can.
But I have taken on board Frits same as piston radius idea , even though 90% of the engines I do have a conical squish area.

[Wos]

CNC is best Equipment wob

To get same radius is not easy to do by hand.

I am using fine sandpaper and polish fluid for aluminium, to radius the plan/ straight squisharea done by lathe

For contol use "mechanics blue" ...kind of paint used for example in metal molding.. between the touching surface of piston and squish..to see footprints that have to be done better...

Hard to explain for me in english cause my last lesson is about 40 years ago😅



Wob? frits...all the others

Do you polish both surfaces too?

Thank you very much!

Grüße Wolfgang

[Frits Overmars]

For contol use "mechanics blue" ...kind of paint used for example in metal molding.. And in dentistry, as I discovered the last few weeks. I've got a bite like a vice grip now :D.


Wob? frits...all the others, Do you polish both surfaces too?I do. The piston dome, the combustion chamber and the exhaust duct are the only surfaces I polish. But not for the sake of flow.
Polishing a surface slows down carbon deposition, but far more importantly, a shiny surface reflects heat radiation. The big difference with a heat-insulating layer is that the surface of such a layer becomes very hot because it does not transfer the absorbed heat to the underlying metal. And that hot surface promotes detonation; not something we are waiting for. A reflective surface also protects the underlying metal against heat radiation, but the surface itself does not heat up.

[lohring]

Speaking of dentistry, I keep thinking the zirconium ceramic alloy we use in crowns would make a good material for engines. It's strong, crack resistant, high temperature and easily machinable in the unfired state. The CNC machining program compensates for firing shrinkage and results in a very accurate final product. Grinding the fired material is straightforward. We use diamond burs and diamond polishing compound. If I still raced ringless piston, small (under 15 cc) engines, I would consider seeing if a dental lab could make some parts.

Lohring Miller
PS For those who didn't know, I've been a dentist for 45 years. Engines are my hobby these days.

[wobbly]

I use increasingly fine wet and dry on the combustion chamber and piston , then polish to a mirror with Mothers Mag Wheel Cleaner.
But never the squish area , my thinking was derived from experiments years ago using ceramics on both the piston and insert , it detonated like hell.
But just coat the chamber and the piston away from the squish and it made more power - simply due to retaining more heat in the combustion process and dumping less into the water , or into the bore via the ring.
Ceramics prevent migration of heat thru the coating to the substrate , but the actual surface is very hot , so by deduction I thought reflected heat from a polished surface into the trapped squish end gases would have the same effect
as a coating.

[Wos]

Very interesting answers form all

Good Example frits...leaving dentist with blue laughing...🙈🤣



Talked not about mirror finish of these surfaceses.. some Materials take no real mirror finish what ever I did...think of its high silicium content

My goal is more to flaten lathe tool " marks" on surfaces of squish to optimice flow ... lets call it medium mirror ..and in my case best possible reflection of heat from crown by minimize its micro surface😌🙃✋

Heared about just polish last few mm of squish to edge....wob?... maybe a compromise🙈🤔🙃

Wolfgang ✋🤔🙃👍🤪

[wobbly]

Deto starts the bottom of the ring /piston seal surface then migrates up to the sharp piston timing edge , so that in my mind dictates what should be shiny and what should not.

[Frits Overmars]

Deto starts the bottom of the ring /piston seal surface then migrates up to the sharp piston timing edge ,
so that in my mind dictates what should be shiny and what should not.In my mind it also dictates what should be sharp and what should not :msn-wink:.

Partly kidding; I use a radiused piston timing edge mainly for reasons of flow and cooling; the Coanda effect makes the incoming cool charge cling to the piston dome.
But the radiused edge also counteracts deto, killing two birds with one stone, Or, as my esteemed colleague would put it: a free lunch.

[Wos]

In my mind it dictates what should be sharp and what should not :msn-wink:.

Partly kidding; I use a radiused piston timing edge mainly for reasons of flow and cooling; the Coanda effect makes the incoming cool charge cling to the piston dome.
But the radiused edge also counteracts deto, killing two birds with one stone, Or, as my esteemed colleague would put it: a free lunch.

Frits!

Wouldn't you teach us more about coanda Effekt? 🤔😉

Seems very effektiv and useful in many ways

Where to use besides of piston edge in a 2 stroke?
How to size radius ...in which place/ circumstanzes/ speeds of flow?

Wouldn't you? 👍🤣✋

Grüße Wolfgang

[Frits Overmars]

Frits!
Wouldn't you teach us more about coanda Effekt? ����
Seems very effektiv and useful in many ways
Where to use besides of piston edge in a 2 stroke?
How to size radius ...in which place/ circumstanzes/ speeds of flow?
Wouldn't you? ����✋My pleasure Wolfgang.
Coanda effect:

http://www.youtube.com/watch?v=AvLwqRCbGKY (http://www.youtube.com/watch?v=AvLwqRCbGKY)

https://www.youtube.com/watch?v=6Q8HssqWDDE


353606

You will find the above info, and a lot of other stuff, in my FOS tips & concepts,
https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41

[Wos]

My pleasure Wolfgang.
Coanda effect:

http://www.youtube.com/watch?v=AvLwqRCbGKY (http://www.youtube.com/watch?v=AvLwqRCbGKY)

https://www.youtube.com/watch?v=6Q8HssqWDDE


353606

You will find the above info, and a lot of other stuff, in my FOS tips & concepts,
https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41

Remember now your pics frits 👍... but was not aware this is called coanda. Sorry.

Whatever...these days teachers have so much more patience with me✋👍 thank you!!!
Coool to be back at school 🤣

Wolfgang

[Frits Overmars]

Remember now your pics frits .. but was not aware this is called coanda. Sorry.It's a bit of everything, Wolfgang. Not just Coanda, but also Bernoulli, Reynolds, De Laval, even a bit of me.


these days teachers have so much more patience with me✋ thank you! Coool to be back at school Teaching can be most rewarding if the students appreciate what you're trying to do. For example, as a volunteer I taught Dutch to asylum seekers who had come to Holland from all over the world. After a few lessons they started to communicate in the only language they all had more or less in common: Dutch.
I had set only one condition: my students had to take the lessons of their own free will and not because participation would give them some privilege
It's the same here: you visit this forum because you want to, and I'll be glad to oblige if I can.

I'll let you in on a little secret. While trying to teach, I also learn myself. I try to explain things as understandably and simply as possible and that forces me to think about the best way to put everything into words. As a result, things sometimes become clearer to me as well. And I'm sure I am not the only one here who has experienced this.

[Wos]

It's a bit of everything, Wolfgang. Not just Coanda, but also Bernoulli, Reynolds, De Laval, even a bit of me.

Teaching can be most rewarding if the students appreciate what you're trying to do. For example, as a volunteer I taught Dutch to asylum seekers who had come to Holland from all over the world. After a few lessons they started to communicate in the only language they all had more or less in common: Dutch.
I had set only one condition: my students had to take the lessons of their own free will and not because participation would give them some privilege
It's the same here: you visit this forum because you want to, and I'll be glad to oblige if I can.

I'll let you in on a little secret. While trying to teach, I also learn myself. I try to explain things as understandably and simply as possible and that forces me to think about the best way to put everything into words. As a result, things sometimes become clearer to me as well. And I'm sure I am not the only one here who has experienced this.

Its more than simple talking here frits!

Triple win for me

Refresh and widen english
Learn and understand more about 2 strokes.
talk discuss communicate to same adicted nice people arround the world

Good job not only for integration of foreigners in netherlands frits👍

At school i was never happy, cause my mother was a teacher and there was a subtle expectation to bring very good certificates 😐🤮

The more happy i am, to be free... free now too learn what i am interested in...without pressure 🥰👍and it feels/ is suddenly easy to learn... wow😎

Be sure frits!!

Have next question in back up✋🤣

Wolfgang

[Storbeck]

Figured this might be a good time to speak up and say thanks to Frits, Jan, Wobbly, Neels, TZ, and all of the other very knowledgeable contributors to this thread. Amazing how much info is on here and shared so freely!

Even more impressive that some of the contributors are speaking in a second language and able to communicate complex subjects so eloquently!

Eventually I'll ask some questions but wanted to start off by showing some appreciation. I've been lurking for quite some time working my way through all of this (there is a lot!) and it really is much appreciated, I'm guessing I'm not the only one that reads but doesn't comment so at least know that we are out there.

[Wos]

Figured this might be a good time to speak up and say thanks to Frits, Jan, Wobbly, Neels, TZ, and all of the other very knowledgeable contributors to this thread. Amazing how much info is on here and shared so freely!

Even more impressive that some of the contributors are speaking in a second language and able to communicate complex subjects so eloquently!

Eventually I'll ask some questions but wanted to start off by showing some appreciation. I've been lurking for quite some time working my way through all of this (there is a lot!) and it really is much appreciated, I'm guessing I'm not the only one that reads but doesn't comment so at least know that we are out there.

Youre welcome Storbeck

Nice true words

Wolfgang ✋

[Pursang]

Thanks to Frits for (re)posting the link to FOS Tips and concepts:niceone:

While looking through this great resource I came across this pic.

353607

It reminded me that back in the 1990's there was an Aussie Automotive Engineer (John Bennett) that did a lot of research on improving the efficiency of older engines, particularly V8's.

One issue he found was dramatically fluctuating coolant temperatures. He determined this was due to the conventional placement of the thermostat on the inlet side of the radiator.

When coolant temperature was sufficient to open the thermostat the entire engine was then flushed with cold coolant from the radiator. This produced variable (mostly poor) combustion.

His solution was to place the thermostat at the bottom of the system where (when required) relatively small quantities of radiator output was blended with the bypass flow to control the input temp and create a more constant engine operating temperature.

353608

He marketed machined alloy components for the bypass and thermostat housing (Eco-Therm?) They were well regarded but probably far too easily copied.
If some 'Bucketeer' wanted to experiment, he/she would have no trouble producing a workable solution

[pete376403]

Thanks to Frits for (re)posting the link to FOS Tips and concepts:niceone:

While looking through this great resource I came across this pic.

353607

It reminded me that back in the 1990's there was an Aussie Automotive Engineer (John Bennett) that did a lot of research on improving the efficiency of older engines, particularly V8's.

One issue he found was dramatically fluctuating coolant temperatures. He determined this was due to the conventional placement of the thermostat on the inlet side of the radiator.

When coolant temperature was sufficient to open the thermostat the entire engine was then flushed with cold coolant from the radiator. This produced variable (mostly poor) combustion.

His solution was to place the thermostat at the bottom of the system where (when required) relatively small quantities of radiator output was blended with the bypass flow to control the input temp and create a more constant engine operating temperature.

353608

He marketed machined alloy components for the bypass and thermostat housing (Eco-Therm?) They were well regarded but probably far too easily copied.
If some 'Bucketeer' wanted to experiment, he/she would have no trouble producing a workable solution

Thats a well known fix for a problem the KLR650 (four stroke, sorry) has. The Thermobob bypass, developed and marketed by Wattman. His web page is well documented with the cooling fluctuations that the standard system encounters as the thermostat opens and closes. IN the case of the KLR - the engine runs far too cool, never gets hot unless the bike is not moving. After fitting the thermobob to my KLR, it quickly heats up to mid temp gauge and stays there.

[Pursang]

The Thermobob is a version of the bypass system shown in Frits' drawing.
It is certainly an improvement on basic non-bypass systems.

The Bennett system has the thermostat sited at the bottom not the top.
It is regulating the coolant Input temperature.


AND...Happy Birthday Frits!:drinknsin

[wobbly]

I have tried the thermo housing at the intake side on the bottom of a couple of racebikes.
Maybe the thermo element body was a bit small , but in both cases the hot running temp ( fully closed bypass ) was a few degrees higher
as I think even a small restriction on the pump inlet side has a large effect , Whereas any restriction seen on the pressure return side has little effect on the flow efficiency.

And Happy Birthday Frits , had no idea you are only a day older than the way I feel.

[SwePatrick]

I´ve got a couple of questions for you guys that have converted your rides to EFI.
In what manner do you add fuel 'when on pipe'?

Compensation relative to crankhouse pressure, or pipe pressure?
Either way, do you use any sort of 'pulse damper device' between source and map sensor?
I reckon the map sensor will live a hard life otherwise.

Rgds
Patrick.

A little video of some of the parts i made and will run:
(nevermind the AMG in the beginning, just an intro)


https://youtu.be/JDoAUQmc094

[Wos]

I´ve got a couple of questions for you guys that have converted your rides to EFI.
In what manner do you add fuel 'when on pipe'?

Compensation relative to crankhouse pressure, or pipe pressure?
Either way, do you use any sort of 'pulse damper device' between source and map sensor?
I reckon the map sensor will live a hard life otherwise.

Rgds
Patrick.

A little video of some of the parts i made and will run:
(nevermind the AMG in the beginning, just an intro)


https://youtu.be/JDoAUQmc094

Nice CNC parts Patrick 👍

In map sonsors can only talk about of KTM 990 4 stroke twin used in mainfold there.
No clue how fast readings of Equipment in this case are. gained about 20 HP by getting rid of the limitations KTM set in injection and ignition timings 🙈🤪

The Ecu is reading the sensors values and is giving decreasing influenz of the two MAPs the higher engine is reving.

In higher revs main influences on injection durations are fix given in table, corelated from values of TPS opening and RPM.
MAP values only have 10 percent influence there.
This is kind of damping in ECU

Think this is the way to go cause you are free to set necessary pulse damping even when pulses are hard and sensor to slow 🤔😉✋

Pure mechanical damping can be done by🤔

Length of hose
Its stiffnes
Its diameter

Avoid overheating sensor🤔

Take care about the fact, that temperature is changing stiffnes off diffrent hose materials ..maybe use metal tube in hot areas


GRÜßE Wolfgang

[TZ350]

I´ve got a couple of questions for you guys that have converted your rides to EFI.
In what manner do you add fuel 'when on pipe'?

Compensation relative to crankcase pressure, or pipe pressure?

MAP, (Manifold Absolute Pressure) is a four stroke thing that has no equivalent in normal two stroke motorcycles. You cant put a MAP sensor on the inlet tract of a two stroke and have it work like it does on a four stroke.

Use Alpha-N (Throttle-Position / RPM) for every where you are on the pipe. But for trailing throttle into a corner, use VE (Volumetric Efficiency) for that and coming back onto the pipe as you exit the corner, MAP / VE.

For a two stroke, MAP can be approximated by the Difference between Max and Min crankcase pressure each cycle. This "Difference" varies with engine load and power output. More power or on the pipe, bigger difference than when throttling off, or trailing throttle.

Some Two Stroke EFI stuff:-

https://www.kiwibiker.co.nz/forums/showthread.php/188733-Suzuki-GT750-EFI-Special

https://www.kiwibiker.co.nz/forums/showthread.php/185773-Speeduino-2T-EFI-Project

Common MAP sensors put out their reading in one milli second bursts. This is what the MAP sensor reading the crankcase pressure on a 125 looks like. Purple line, Yellow line is the Ignition trigger.

353609 1,800rpm 353610 4,000rpm 353611 10,000rpm

I used an Arduino Nano to find the Difference between the high and low reading each cycle and converted the Difference using a Digital to Analog card to get something that looks like a normal four strokes MAP value to feed into the EFI's CPU.

353612

Alpha-N gets used everywhere that it is on the pipe, or definitely not on the pipe. I.E., us Alpha-N when the load is predictable. MAP and VE is used where the pipe is not sure if it is "On" or not.

If you are running Alcohol fuel I would not worry and just use the Alpha-N topology everywhere.

[Wos]

MAP, (Manifold Absolute Pressure) is a four stroke thing that has no equivalent in normal two stroke motorcycles. You cant put a MAP sensor on the inlet tract of a two stroke and have it work like it does on a four stroke.

Use Alpha-N (Throttle-Position / RPM) for every where you are on the pipe. But for trailing throttle into a corner, use VE (Volumetric Efficiency) for that and coming back onto the pipe as you exit the corner, MAP / VE.

For a two stroke, MAP can be approximated by the Difference between Max and Min crankcase pressure each cycle. This "Difference" varies with engine load and power output. More power or on the pipe, bigger difference than when throttling off, or trailing throttle.

Some Two Stroke EFI stuff:-

https://www.kiwibiker.co.nz/forums/showthread.php/188733-Suzuki-GT750-EFI-Special

https://www.kiwibiker.co.nz/forums/showthread.php/185773-Speeduino-2T-EFI-Project

Common MAP sensors put out their reading in one milli second bursts. This is what the MAP sensor reading the crankcase pressure on a 125 looks like. Purple line, Yellow line is the Ignition trigger.

353609 1,800rpm 353610 4,000rpm 353611 10,000rpm

I used an Arduino Nano to find the Difference between the high and low reading each cycle and converted the Difference using a Digital to Analog card to get something that looks like a normal four strokes MAP value to feed into the EFI's CPU.

353612

Alpha-N gets used everywhere that it is on the pipe. VE is used where the pipe is not sure if it is "On" or not.

If i had these experts words👍🤩

If you put pressure sensor to pipe in a 2 stroke?... there is absolutely no usable signal, to recognice ...we are on or off pipe?

Thanks to experts! 👍😎

Wolfgang

[Pursang]

I have tried the thermo housing at the intake side on the bottom of a couple of racebikes.
Maybe the thermo element body was a bit small , but in both cases the hot running temp ( fully closed bypass ) was a few degrees higher
as I think even a small restriction on the pump inlet side has a large effect , Whereas any restriction seen on the pressure return side has little effect on the flow efficiency.

Hi Wobbly, I'm not sure I understand?? In the Bennett system, the bypass is always Fully Open.
The thermostat element is constantly exposed to the bypass flow.
At it's design temperature it opens to allow input of coolant from the radiator (Flow through the thermostat valve is reverse)
Opening temperature of the thermostat element may need to be varied to achieve the desired max operating temp.
Mixing chamber volume, flow path and/or thermo element shielding are design considerations.
The bypass hose diameter and top diversion junction should be configured to provide minimal restriction to the pump input.

Bennett found that a stable operating temperature was essential to achieve optimum combustion efficiency in 150+ kg of Cast Iron.
I expect it is infinitely more critical in a couple of kg of aluminum with more holes than metal.

[SwePatrick]

Nice CNC parts Patrick 👍

In map sonsors can only talk about of KTM 990 4 stroke twin used in mainfold there.
No clue how fast readings of Equipment in this case are. gained about 20 HP by getting rid of the limitations KTM set in injection and ignition timings 🙈🤪

The Ecu is reading the sensors values and is giving decreasing influenz of the two MAPs the higher engine is reving.

In higher revs main influences on injection durations are fix given in table, corelated from values of TPS opening and RPM.
MAP values only have 10 percent influence there.
This is kind of damping in ECU

Think this is the way to go cause you are free to set necessary pulse damping even when pulses are hard and sensor to slow 🤔😉✋

Pure mechanical damping can be done by🤔

Length of hose
Its stiffnes
Its diameter

Avoid overheating sensor🤔

Take care about the fact, that temperature is changing stiffnes off diffrent hose materials ..maybe use metal tube in hot areas


GRÜßE Wolfgang

Nice thanks for the answer, i´ve bought maxxecu mini, it has an 3bar mapsensor built in.
I was thinking of using an fuelfilter(carburetor seethrough) with a restrictor on the 'intake side' that makes the air inside the filter to soften up the pulses that are going into the mapsensor.

[SwePatrick]

MAP, (Manifold Absolute Pressure) is a four stroke thing that has no equivalent in normal two stroke motorcycles. You cant put a MAP sensor on the inlet tract of a two stroke and have it work like it does on a four stroke.

Use Alpha-N (Throttle-Position / RPM) for every where you are on the pipe. But for trailing throttle into a corner, use VE (Volumetric Efficiency) for that and coming back onto the pipe as you exit the corner, MAP / VE.

For a two stroke, MAP can be approximated by the Difference between Max and Min crankcase pressure each cycle. This "Difference" varies with engine load and power output. More power or on the pipe, bigger difference than when throttling off, or trailing throttle.

Some Two Stroke EFI stuff:-

https://www.kiwibiker.co.nz/forums/showthread.php/188733-Suzuki-GT750-EFI-Special

https://www.kiwibiker.co.nz/forums/showthread.php/185773-Speeduino-2T-EFI-Project

Common MAP sensors put out their reading in one milli second bursts. This is what the MAP sensor reading the crankcase pressure on a 125 looks like. Purple line, Yellow line is the Ignition trigger.

353609 1,800rpm 353610 4,000rpm 353611 10,000rpm

I used an Arduino Nano to find the Difference between the high and low reading each cycle and converted the Difference using a Digital to Analog card to get something that looks like a normal four strokes MAP value to feed into the EFI's CPU.

353612

Alpha-N gets used everywhere that it is on the pipe, or definitely not on the pipe. I.E., us Alpha-N when the load is predictable. MAP and VE is used where the pipe is not sure if it is "On" or not.

If you are running Alcohol fuel I would not worry and just use the Alpha-N topology everywhere.

Nice info, yes my plan was alpha-n mapping.
And just have been told that you need to compensate for pipepressure when 'on the pipe'
I have always thought 'that seems unnecessary' as what i´m doing is dragracing and just having it wide open whole track ;)
And as you write, alcohol makes it even more less sensitive to some 'bad mapping' where it could be a little bit rich(off pipe)

Rgds.

[Wos]

Nice thanks for the answer, i´ve bought maxxecu mini, it has an 3bar mapsensor built in.
I was thinking of using an fuelfilter(carburetor seethrough) with a restrictor on the 'intake side' that makes the air inside the filter to soften up the pulses that are going into the mapsensor.

For further Diskussion Patrick👍

I have used name MAP sensor for a sensor in mainfold in 4 stroke

Think its Important now to find best placement of sensor for your specific requirement... in your 2 stroke 👍😎✋

For myself I recogniced... there are realy better experts than me in special injection questions👍

OlFashionedCarbType in 2 strokes 🙈😉🤣

Wolfgang

[TZ350]

... my plan was alpha-n mapping ... as what i´m doing is dragracing and just having it wide open whole track ...

Yes, easy. Alpha-N, TPS vis RPM will be all you need for Drag Racing.

"MAP" manifold absolute pressure and "IAT" inlet air temperature sensors placed to measure outside atmosphere to compensate for changes in relative air density on the day.

[wobbly]

Hi Pursang , the issue with the " conventional " thermostat controlled system in a usual automotive situation is that they are only single acting.
As the restricted water flow heats up , it opens the plate valve and allows water to flow progressively more thru the radiator.

But in a 2T race situation it is all but impossible to have overcooling once the valve has fully opened.
On very cold days we can of course use tape over the rad to increase the engine operating temp , but when the optimum temp is under 45* this situation is rare.
In a double acting thermostat setup , the valve operates on both loops , closing one , as it opens the other , and can maintain the temp no matter how cold the ambient.

This is what I used to build 100s of for karts and race bikes, with the valve starting to work at 42 *C and was fully open at 45.

[SwePatrick]

Yes, easy. Alpha-N, TPS vis RPM will be all you need for Drag Racing.

"MAP" manifold absolute pressure and "IAT" inlet air temperature sensors placed to measure outside atmosphere to compensate for changes in relative air density on the day.

Yes, i was planning mounting the IAT sensor very close to the intake.
The MAP sensor is built in into the ECU, nice feature actually.

[Wos]

My fellow and i having a new project:niceone:

Its a Puch Frigerio Gs 125 Enduro from 1980 for classic enduro sports in germany..

Its engine is a rotax 124 gs with rotary valve inlet.
RV is new for me to optimice and for enduro use, on this engine is a special long duct, to keep carb inside frame of the bike.

Surely long intake duct is a disadvantage in highend power 2 stroke??

But maybe good for torque in lower revs, that we want in enduro use?

Stock bikes with this rotax ( swm, kramer, kramit, puch frigerio) have torque like hell ;) ��...but dont reve ��

Is somebody out, who can give first little help ...view...what we have to expect in case of this big air/ fuel mass between carb and RV...and which way is to go, to tune duct ( size like carb 34mm) by keeping its length...for first shot, tell you length about 200 mm... oh ��

Maybe a diameter change ? Or a nozzle inside could shift parameters to higher revs?

Try to add first photo..

But found more terrible things rotax in the 80ies did ! :) never seen tings like this head...exwindow...will show you next days fellows ;)

Tanks! :niceone:

Grüße Wolfgang

[Pursang]

But in a 2T race situation it is all but impossible to have overcooling once the valve has fully opened.
On very cold days we can of course use tape over the rad to increase the engine operating temp , but when the optimum temp is under 45* this situation is rare.
In a double acting thermostat setup , the valve operates on both loops , closing one , as it opens the other , and can maintain the temp no matter how cold the ambient.

This is what I used to build 100s of for karts and race bikes, with the valve starting to work at 42 *C and was fully open at 45.

Thanks for that, wobbly. Double acting thermostat changes things. So does your knowledge and experience!:o

[wobbly]

WOS , with a Rotary valve on a race engine it is all but impossible to mechanically make the intake too short.
Cut off that huge duct and make a pad on the cover to fit an off the shelf Mikuni oval carb rubber manifold.
This will get you real close , real quick.

[Wos]

WOS , with a Rotary valve on a race engine it is all but impossible to mechanically make the intake too short.
Cut off that huge duct and make a pad on the cover to fit an off the shelf Mikuni oval carb rubber manifold.
This will get you real close , real quick.


Pleasure for us reading from you wobbly !!

Will shorten as we can... but sideways carb is in enduro bad for carbs life in case of falling 😞 hitting sideways a tree...


In the Moment we are evaluating possible ways to go...

Soooo nice to have all the pros advice here! Wow!!

Will continue asking and learning ;) for sure in case of special RV Questions...top !!


Thanks a lot



Grüße Wolfgang

[F5 Dave]

What odd things come out of the woodwork. Sadly you will need filtration and that horrible compromise will be an eye closed venture.

I remember riding a GP100 roadbike with knobblies downhill. There was a small log. A quick blip was called for. Quick flick of throttle .
Bleeer.
Thud over log. . . Braap.

Thought about it. RV had loaded up downhill and taken a while to clear.

Are you stuck with this engine?

[Frits Overmars]

WOS , with a Rotary valve on a race engine it is all but impossible to mechanically make the intake too short.
Cut off that huge duct and make a pad on the cover to fit an off the shelf Mikuni oval carb rubber manifold.
This will get you real close , real quick.I put the rubber manifold inside the clutch cover, looking out. Got us real close, real quick :msn-wink:
PS: the carb on the picture is not the one I used. I fitted an ultra-shortened 38 mm Mikuni in 1979. This picture of my engine turned up 39 years and umpteen owners later.
353619

[Wos]

What odd things come out of the woodwork. Sadly you will need filtration and that horrible compromise will be an eye closed venture.

I remember riding a GP100 roadbike with knobblies downhill. There was a small log. A quick blip was called for. Quick flick of throttle .
Bleeer.
Thud over log. . . Braap.

Thought about it. RV had loaded up downhill and taken a while to clear.

Are you stuck with this engine?

Tanks Dave, wob and frits,

The frigerio was the choice of my friend and driver. He fellt in love with the bike :eek:

But i was aware this will be hard to tune. As backup, if we fail, we have strongest reed bike in the competition, a TGM.

In reglementation we can change engine, but have to keep year and aircooled

Tracks vary from race to race. From more cross to more hillclimbing or trail sections.

But we could change bike from race to race and the puchs seathight is bit lower, better for some races ;)

Rotax advertised 28 hp and to tell you an range that we dream for ;)... lets say real 32 hp

Found many things we can do better

Head has no squish area!!!

Exwindow has widest area after blowdown... never seen!! Oh ... about bit over 40mm!!! Transfers aimings ar nearly horizontal

Bosch HKZ with heavy rotor...not programmable

Rod, piston and pin are heavy

Exducts ending 39mm

Pipe to shallow

Roundslide carb

Frits!! You better tell us engines that are NOT touched by you!!!! ??? :clap:

Please tell us more secret specs from your rotax 124 :psst: and if you would...the storys behind it :cool:

Tanks a lot !!

Grüße Wolfgang

[Frank S.]

Hi Wolfgang,
if you mount the carb on the side, just make a cage of some steel pipes to protect it. Inside the cage might be room for an airbox with the carb inside it.
This cage can also protect the driver's leg when hitting a tree.
Grüsse Frank

[Wos]

Rotax horror pics

Folks!

If you are to weak for...immediatly close your eyes!!! :killingme

This ist stock GS ( in german GELÄNDE SPORT) offroad sports zylinder with iron cast sleeve

Try to get a rare alu nikasil aircooled next ;)

[Wos]

Hi Wolfgang,
if you mount the carb on the side, just make a cage of some steel pipes to protect it. Inside the cage might be room for an airbox with the carb inside it.
This cage can also protect the driver's leg when hitting a tree.
Grüsse Frank

Tanks neighboor frank,

Every idea welcome!

Let us discuss from face to face after liedolsheim race, having some beers in front of the object of love :woohoo: ;) you are invited

This will be a long term project for autum and winter

:drinknsin

Have a nice holiday in france! ✌😎

Wolfgang

[Frank S.]

Tanks neighboor frank,

Every idea welcome!

Let us discuss from face to face after liedolsheim race, having some beers in front of the object of love :woohoo: ;) you are invited

This will be a long term project for autum and winter

:drinknsin

Have a nice holiday in france! ✌😎

Wolfgang
🍻maybe we will drink from the winner cup😎

[Peter1962]

Tanks Dave, wob and frits,

The frigerio was the choice of my friend and driver. He fellt in love with the bike :eek:

But i was aware this will be hard to tune. As backup, if we fail, we have strongest reed bike in the competition, a TGM.

In reglementation we can change engine, but have to keep year and aircooled

Tracks vary from race to race. From more cross to more hillclimbing or trail sections.

But we could change bike from race to race and the puchs seathight is bit lower, better for some races ;)

Rotax advertised 28 hp and to tell you an range that we dream for ;)... lets say real 32 hp

Found many things we can do better

Head has no squish area!!!

Exwindow has widest area after blowdown... never seen!! Oh ... about bit over 40mm!!! Transfers aimings ar nearly horizontal

Bosch HKZ with heavy rotor...not programmable

Rod, piston and pin are heavy

Exducts ending 39mm

Pipe to shallow

Roundslide carb

Frits!! You better tell us engines that are NOT touched by you!!!! ??? :clap:

Please tell us more secret specs from your rotax 124 :psst: and if you would...the storys behind it :cool:

Tanks a lot !!

Grüße Wolfgang


Talk to Fletner, he has extensive knowledge on how to change an old rotary valve aircooled engine (kawasaki big horn 350) by dumping the carburator and mounting fuel injection. The long intake duct can still be used for air intake, but the injection can be mounted very close to the rotary valve.

[Wos]

Talk to Fletner, he has extensive knowledge on how to change an old rotary valve aircooled engine (kawasaki big horn 350) by dumping the carburator and mounting fuel injection. The long intake duct can still be used for air intake, but the injection can be mounted very close to the rotary valve.

Peter ...thanks ;)

My knowledge is to small for injection...as the pocktets of us��

Made first measure of space between crank and crankcase...distance is small...so my guess is that we have relatively small free volume ;)

Maybe its one additional way to gain some power to enlarge case free volume? Frits...? �� Good idea?

[wobbly]

Rotary Valve engines can use bigger case volumes - under 1.3 , the Aprilia was 1.24 and was helped by using a long rod.
This may be easy to do in your engine and fit a plate under the cylinder.

[Wos]

Rotary Valve engines can use bigger case volumes - under 1.3 , the Aprilia was 1.24 and was helped by using a long rod.
This may be easy to do in your engine and fit a plate under the cylinder.

Yes wob ;) merci!

Thats next option besides milling crankcase 😀

Original piston pin is 18 mm ...conrod 110

From rotax 122 there is a rod for piston pin 15mm in 110 and 115mm length

Then we can use light suzuki motocross piston, everywhere available ;)

Grüße Wolfgang

[Frits Overmars]

Frits!! Please tell us more secret specs from your rotax 124If memory serves, I once posted the specs in a forum, probably in Pit-Lane, but I'm not sure.
Later.....
I've been searching through Pit-Lane for half an hour now, without finding what I was looking for, so I will leave the searching to you.
One thing I do remember: Rotax used an inlet disc with an ultra-late closing timing because of the ultra-long inlet tract in the original Rotax 250 engine, on which the Rotax 124 was based. I encountered that same disc timing in the '124' and about the first thing I did, was to mount the disc one tooth (16°) earlier without altering the disc itself.
Then I shortened the disc cover stub and I enlarged the hole in the clutch cover, so I could fit a Mikuni inlet rubber between the disc cover and the inside of the clutch cover, and I enlarged the inlet tract diameter from 34 mm Ø to 38 mm Ø.
How and why I modified the cylinder, is posted 'somewhere' in the internet. If you manage to find it, please let me know where.

[Wos]

If memory serves, I once posted the specs in a forum, probably in Pit-Lane, but I'm not sure.
Later.....
I've been searching through Pit-Lane for half an hour now, without finding what I was looking for, so I will leave the searching to you.
One thing I do remember: Rotax used an inlet disc with an ultra-late closing timing because of the ultra-long inlet tract in the original Rotax 250 engine, on which the Rotax 124 was based. I encountered that same disc timing in the '124' and about the first thing I did, was to mount the disc one tooth (16°) earlier without altering the disc itself.
Then I shortened the disc cover stub and I enlarged the hole in the clutch cover, so I could fit a Mikuni inlet rubber between the disc cover and the inside of the clutch cover, and I enlarged the inlet tract diameter from 34 mm Ø to 38 mm Ø.
How and why I modified the cylinder, is posted 'somewhere' in the internet. If you manage to find it, please let me know where.

Hope i could do you a favour frits...but you did bigger for me within spend your time for me!

Wow...frits is wasting time only for me!! ?...for us!? Applause from me in the name of all gasheads here...������

Frits OvermarsJeu 13 Juin 2013 - 17:12
par Frits Overmars
By '2 mm clearance' I assume you mean 1 mm either side between crank and case, and 1 mm between outer crank radius and inner case radius. Viscous drag increases strongly below 1 mm clearance; enlarging the clearance beyond 1 mm has only a limited effect on viscous drag. So if increasing the clearances beyond 1 mm improves power, I would assume that this improvement was caused by the increased crankcase volume. It could also have been caused by improved inlet flow, but I cannot comment on that without knowing your engine so I will leave this aside for now.

The most striking example of crankshaft clearance I saw in the old Rotax-124 kart engine that I worked on from 1978 onward. It was really a 250 cc motocross engine with a 125 cc crank in it. If I remember correctly the case diameter was about 12 mm larger than the crank diameter! But it was easily the fastest engine of that era, and the most susceptible to tuning modifications. It was also the grandfather of the Aprilia RSW125 Grand Prix engine

And

http://www.pit-lane.biz/t4072p250-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-3-locked?highlight=frits

Pleasure for me if you were searching this

Your writing 2013 went round and round in my head...

12 mm space...wow...have further questions as we have much less space/volume free

Merci danke thanks ��✋


Wolfgang

[Wos]

The night is young here in europe frits! Isnt it ;)

So I have a question to you

Is increasing small free volume of crankcase with this uggly long intake duct ;) ..effctiv too?

Did you tested this ? Or only with carb direct on rotary case?

Rotax long intake duct Function is clear to me...only giving carb protected Position, that we need in enduro use...

And..we should not worry about things that are not available in the moment...new circumstance...and we have to find new fitting answers? Your great findings will never fit perfekt for my expectations...for example enduro engine!?... so how could Iexpect clear numbers frits? :no:

Make us understand physiks of 2 stroke...as you did/ tryed... :killingme...if impossible...still continue tryings ...please :psst:





Tank you frits so so much!

Grüße Wolfgang

[Wos]

For last 3 days.... late later closing disc timing was my conclusion for Stock long duct

Cause of long duct with big slow moving mass inside?
To use a kind of charching effect of its energy in action!?

Do you agree?

Danke!

Wolfgang

[190mech]

Wos,
We ran the CanAm motorcycles (Enduro and Motocross) back in the 70's that had that engine. In that time it was a great engine! It had a wide powerband, good transmission ratios and was reliable. We liked the 175 as it would keep up with the 250's on the long dirt roads between trail sections, the weak points were the CDI which was very expensive to replace and the rotary side crank seal leaking causing bad smoking..We ran them basically stock except for some pipe work and lots of frame modifications to increase suspension travel.

[Wos]

Wos,
We ran the CanAm motorcycles (Enduro and Motocross) back in the 70's that had that engine. In that time it was a great engine! It had a wide powerband, good transmission ratios and was reliable. We liked the 175 as it would keep up with the 250's on the long dirt roads between trail sections, the weak points were the CDI which was very expensive to replace and the rotary side crank seal leaking causing bad smoking..We ran them basically stock except for some pipe work and lots of frame modifications to increase suspension travel.

Nice to hear your review 190mech!
In classic enduro competition the Rotax still is often in use, but most of them are bone stock.
175 are very rare, most are 125cc

Tomorrow is next race in south of germany

https://www.moc-steinsberg.de

We take part with tgm 125 and hrd 75cc, both well tuned within regulations, no part untouched, for example programmable lightweight hpi ignition, fine suspension from race division of yss ;)

Same we want do next months to the puch frigerio rotax ;)

Grüße Wolfgang

[Frits Overmars]

Is increasing small free volume of crankcase with this uggly long intake duct effctive too? Did you test this ? Or only with carb direct on rotary case?If you increase the crankcase volume, you lower the Helmholtz frequency of the inlet system, so the engine wants to producve its maximum torque at lower revs. But the exhaust pipe has to agree, otherwise: no deal, unless you restore the original Helmholtz frequency with a longer inlet timing.
But that was already damn long to begin with. It would make carburation quite moody, so that's about the last thing I would do to a dirt bike.

Did I test it? Yes. Not with the original Rotax inlet tract, but with an elongation piece between carb and disc. It led to the following story (that you can find, together with a lot of other short stories, in my FOS tips & concepts):
https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41
=================================================
In all inlet systems the inlet flow accelerates as long as the pressure upstream of the inlet tract is higher than the downstream pressure.
When both pressures are equal the flow has reached its maximum velocity and because mixture keeps entering the crankcase, the case pressure rises above the upstream pressure and this rising pressure gently slows the flow down to a standstill (or suddenly instead of gently if the inlet port closes too soon, which can happen in both piston port and rotary induction systems).
In any case, the pressure at the crankcase side of the inlet tract will then be higher than the pressure at the bellmouth, and mixture will start flowing back towards the free world. The extend of this backflow may be so small that it is not noticeable at the bellmouth, but it is happening nevertheless. Reed valve systems do it just as much as other inlet control systems.

I call this phenomenon bounce-back and it should not be confused with the blow-back that occurs when an inlet port closes too late.
Bounce-back mixture never really made it into the crankcase; it returned at the closed door.
Blown-back mixture initially entered the crankcase but then reversed its flow direction because of the rising case pressure before the case was closed.
This rising case pressure resulting in flow reversal has rather little to do with the piston moving down after TDC. It can even happen before TDC if the Helmholtz frequency of the inlet system is too high for the engine revs (low revs, big carb diameter, short inlet tract, small case volume).

By the way, bounce-back may be hardly noticeable, but on the other hand it can be even more vicious than blow-back.
As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disc closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.


Make us understand physics of 2 stroke...as you didPhysics is something you study; not many shortcuts, or as Wobbly would put it: no free lunch (he must be thinking with his stomach).
But I've got something better to offer: logic. Anyone can do it and in my opinion logic is more important than mathematics and physics together.

[Wos]

If you increase the crankcase volume, you lower the Helmholtz frequency of the inlet system, so the engine wants to producve its maximum torque at lower revs. But the exhaust pipe has to agree, otherwise: no deal, unless you restore the original Helmholtz frequency with a longer inlet timing.
But that was already damn long to begin with. It would make carburation quite moody, so that's about the last thing I would do to a dirt bike.

Did I test it? Yes. Not with the original Rotax inlet tract, but with an elongation piece between carb and disc. It led to the following story (that you can find, together with a lot of other short stories, in my FOS tips & concepts):
https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41
=================================================
In all inlet systems the inlet flow accelerates as long as the pressure upstream of the inlet tract is higher than the downstream pressure.
When both pressures are equal the flow has reached its maximum velocity and because mixture keeps entering the crankcase, the case pressure rises above the upstream pressure and this rising pressure gently slows the flow down to a standstill (or suddenly instead of gently if the inlet port closes too soon, which can happen in both piston port and rotary induction systems).
In any case, the pressure at the crankcase side of the inlet tract will then be higher than the pressure at the bellmouth, and mixture will start flowing back towards the free world. The extend of this backflow may be so small that it is not noticeable at the bellmouth, but it is happening nevertheless. Reed valve systems do it just as much as other inlet control systems.

I call this phenomenon bounce-back and it should not be confused with the blow-back that occurs when an inlet port closes too late.
Bounce-back mixture never really made it into the crankcase; it returned at the closed door.
Blown-back mixture initially entered the crankcase but then reversed its flow direction because of the rising case pressure before the case was closed.
This rising case pressure resulting in flow reversal has rather little to do with the piston moving down after TDC. It can even happen before TDC if the Helmholtz frequency of the inlet system is too high for the engine revs (low revs, big carb diameter, short inlet tract, small case volume).

By the way, bounce-back may be hardly noticeable, but on the other hand it can be even more vicious than blow-back.
As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disc closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.

Physics is something you study; not many shortcuts, or as Wobbly would put it: no free lunch (he must be thinking with his stomach).
But I've got something better to offer: logic. Anyone can do it and in my opinion logic is more important than mathematics and physics together.

Thank you very much frits!

Your text making me see a heavy slow accelerated ...coming to late head... bouncing a closing disc... :brick: thank you ! :D:niceone:

Your conclusion do not lengthen conrod...do the oposit
??

Yesterday saw aftermarket pipe of swm rotax ... clearly to short i thought ... about 900mm...we thougt about 110 cm...or more
To come more in frequency of that long inlet tunnel...case Helmholtz swinging system

The pipe resonance would be then about 8500...or even deeper

But after your words my stomach says/ asks...could that be deep enough?

Wether me, nor my stomach are dr. Physics...so wonderfull we can ask frits :yes: top

Many thanks frits

Grüße Wolfgang

[Frits Overmars]

Your conclusion do not lengthen conrod...do the opositWhere did I say that??

[Wos]

Where did I say that??

Sorry frits

Was my conclusion in the end...thougt you would conclude ...if i understood your text...

Have to be more careful ;)

Had a look to a nikasil type :)

Much better main exhaust port i think

Grüße Wolfgang

[koenich]

🍻maybe we will drink from the winner cup😎
We'll try to avoid that ;) see you tomorrow!

cheers #29

[SwePatrick]

Having the advantage of designing my intake any way i want, i am curios about what would you say is the 'optimal' velocity stack design for a short intake twostroke engine?

My throttlebody is as we speak only 32mm long and i haven't calculated with the stacks yet, i´ve been looking at RSA ofcourse.
But is that design best for reed intake?

I can now choose about any design i want.

Diam is as we speak 38mm due to problem with space for the internal slide between the bolts, but i can later mill the openings somewhat oval to get more area if needed.

I have been simulating in MOTA that i lose about 300rpm at midrange, but gain almost 1000rpm longer 'peak power', this from 114mm long intake to 32mm(not calculating with reed length)
But the stack design is a little bit of a queston for me i need straighten out.

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[Frank S.]

We'll try to avoid that ;) see you tomorrow!

cheers #29

Catch me if you can😁
... see you...
#39 Lucky losers racing team

[OopsClunkThud]

Here's the proportions of Blair's "ideal bell" along with the effective length above the bell from Wobbly.

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Rather than having to remember or look it up each time, I start with this drawing and scale it as needed.

[wobbly]

The effective intake tract length is as per the bell drawing with the "end correction " added , but my research during a PhD project showed you should use 2/3 of the petals actual free
length in the sim as the length changes as the tips lift ( plus any length up to the clamp point ).