ESE's works engine tuner

[TZ350]

Will you point the rear angle of the secondary's transfers really towards the exhaust?

I was planning on a rear transfer like the one on the left in your picture. I have heard about having a hook in the transfer and imagined that was what the one in the picture was.

Once I had a little experience, a cylinder I was working had that angle, almost towards the center of the exhaust, then I opened the secondarys to give more area, just a bit, without knowing I changed that angle and now was directed more to the main transfers, as result I felt I had loss a bit of peak power, but the engine was broader and bottom end seemed a bit better to. This was way before Frits exposed the pizza tower concept on pit-lane. My thoughts were that short circuiting to the exhaust at some point would compliment the power when the exhaust is working on his ideal resonance rpm.

Thanks for the tip, I will look at this some more.



Yes your right, it looks like the type 2 boost port will be better.

Filling the transfers with epoxy to make the final internal angles might even help keep the gases a little cooler before entering the cylinder than if they are exposed to the aluminum. Right? Regards

I am going to position the injectors in such away that any excess wet fuel impinges on the transfer walls, the idea being that as it evaporates it also cools the cylinder. 2-Strokes have always been fuel cooled to some extent, I am just going to make a virtue from it.

[TZ350]

Page 760 .....

I have looked and read that info about pipes twice. Very Useful.

Thing is, when I was using the demo Expansion Chamber Design Prog (http://www.bevenyoung.com.au/mota.htm) that is very used here and having all the Honda desing's in the table I notice that Mota makes ultra sharp final diffuser cone, so the previous exhaust's I built all have around 11º degree diffuser angle, the mid section is longer, and the diffuser starts later than the 30/33% rule of thumb.

Other thing is all Honda Exhaust have the last diffuser the steepest one, and Aprilia uses the other concept of biggest and longest middle diffuser, I would like to know if anyone used a pipe in Honda RS with the Aprilia type.

I just want to discuss the angles and length's.

Here is the hell RS125 pipe design that has basically everything I know embedded in its concept, the 800mm length is for a 200* Ex only with a
proper ignition curve and powerjet switching.

The first 25 mm is an oval transition flange ( 41 by 32 ) in the duct, out to a 41 header.
The stinger nozzle is 23.2 with 25 stinger pipe. Dual stage header, and steep mid diffuser create the deepest and widest depression around BDC at 13,000, with tons of overev power.

The 120mm Honda and Mota pipes wont even get close, especially with the final diffuser being the steepest,it creates the Ex port depression way too late in the cycle to help at the natural peak of a 200* Ex around 13,000 and into the all important overev past 14,000.

Several details can be jigged to work better than this design, but thats for you guys with a good code to work with to figure out from looking closely at the pressure ratio traces.

For this top bmep engines we use 14º baffle angles, right, and if we go for slower less reving bikes, should we decrease this angle right? I have seen an amount of longer pipes (both handmade and aftermarket), like 950 and 1000 mm lenght for bikes who get peak power around 9k/10k rpm that have short baffles, like the ones of RS lenght, and the YZ and CR 125 have very long baffles.

So I guess someone is doing a really bad job.

Made an Exhaust for a friend with a DTR 125 (peak at 9500/10000), using one 235mm 12,1º baffle, worked better against a known good aftermarket exhaust, my friend already sold the aftermarket pipe....

The position of the start of the mid diffuser is the key to making top end and overev power.
Earlyer Aprilia and Honda designs had the steep diffuser starting right after the header, but this pulls the Ex depression down too early around BDC.

It works alot better for power production to space the main cone further along, and make the angle steeper to promote higher depression values by using a shallow last diffuser angle.
This also increases the main body volume.

I have been making the first and last diffusers around the same angle, just coz it feels right, and the sim says fill your boots.
Steep rear cones will work on any engine needing a high specific output, but you must have a digital ignition and powerjet switching, to stop the fast powerdrop off past peak that the short cone will naturally create.

A longer rear will suppress the peak value and allow more natural overev characteristics without digital trickery.

I also believed what I had been told previously ,that large changes in initial diffuser angle would cause flow separation and massive turbulence due to choking.
I built a heap of pipes to come up with a new design for CR125 Moto in SKUSA racing.
One of the tests was to try a design similar to the older Aprilia, with a very steep diffuser directly after the header.
This pipe made good power, but i was sure that if I added a short 25mm section ( the length of a bend segment in the U bend ) between the header and the main diffuser, with
only 1/2 the angle change - it would make more power.
Sadly no free lunch, it was worse by a small margin - bugger, another wives tale down the dunny.
I went on to discover the relationship of best power production, to the shape of the depression waves amplitude around BDC - was super critical to where the main diffuser started.

You have to be careful when using retard to heat the pipe in the overev.
If you continue the retard slope too far,especially if the motor then continues to make serious power - the egt will continue to rise with rpm, and you then end up running a richer main to suppress the now too high egt.
This means you are using fuel to cool, not burning it to make power.
You must flat line the ignition retard as soon as you can in the overev, to stabilise the egt when running full throttle at those peak revs.

You have got the wrong end of the stick re pipe temp Romeu, the highest temp is seen just into the header, the lowest in the belly, and it increases again at the stinger.
Lower temps are seen right at the flange, due to unburnt air/fuel sitting there waiting to be shoved back in.
Aprilia used probes in the flange due to reliability issues I understand,but they would for sure have found a correlation between the readings there, and the " normal " one along the header.

Three angle rear cones were a legacy design that Jan was forced to use, as Frits explained.
But it is a long time issue for me that so often a sim will be strongly telling me that the system works well ( and it annoys Neels as well I know ) but in reality I have never been able to get more power on the dyno
than a 14* straight tailcone - believe me I have waisted so much time on this, and have given up.

In a KZ2 125 kart engine with the main Ex port opening at 82.5* you would normally have the Aux about 1.5mm lower - lift them up flat and you loose around 3 Hp at 10,000, 1 at peak 13,000, but worst is
up to 6Hp at 14,000 where the curve is dropping rapidly.
I tested a cylinder with the main down at 84* and the ports all opening flat made the most power there, but sadly that power was well down on what is possible with a higher main and staggered Aux.

Re the diffuser position for RS125 - the Aprilia rotary valve engine was , by design, run to 14500 on track, so was able to use the slightly shorter header end position.
The reed valve Honda is virtually impossible to get to run up there with any effective gains, so makes more power in its useable band with the slightly longer header.

If I were to explain pipe design I would need to write a book,but in general things are pretty straight forward in relation to the % values.
End of header is always 31 to 33% and end of diffuser is always 62 to 68%.
To see the effect of a silly long header, you can watch the pressure ratio at the Ex port, and thus the effect this has on the depression in the cylinder.
We are looking for the lowest and widest negative ratio we can get around bdc when the transfers are fully open.
A long header delays the beginning of the depression too late in the cycle, when in the power band.

The % I quoted for header means that portion of the length from piston to rear cone end.
Its from the piston to the beginning of the diffuser, what happens in between isnt relevant.
Unless of course you use a small Ex duct and a bigger header, that makes more power.
And of course same for the diffuser end, that is simply 66% of the length from the piston to the end of the rear cone.

So to start with, I understand some of the key elements are.

(1) The end of header is always 31 to 33%

(2) The end of diffuser is always 62 to 68%.

(2) We are looking for the lowest and widest negative ratio we can get around bdc when the transfers are fully open.

Time to warm up my EngMod2T program and use the Pipe Development part of it to get started.

In a race 2T we are always fighting power range Vs peak power.
Shorter diffusers create steeper angles,thus greater wave amplitude, but this narrows the effective band width.
So - in general the best compromise is around 66%.

The plan is a peaky pipe at 9k rpm and to extend its range using the Trombone effect.

The short answer is yes. But why is it that each time you people sit down for five minutes to write a question, I have to sit down for two hours to write an answer?

When the exhaust port opens, a pressure pulse starts moving through the exhaust pipe. It is reflected at the end cone and it should be back at the cylinder just before the exhaust port closes.
Next a part of this reflected pulse bounces off the partly-closed exhaust port and a residual pulse starts moving down the exhaust pipe. This residual pulse too is reflected by the end cone and starts moving back to the cylinder. Ideally it will arrive at the exhaust port just when the port opens again. Then the cylinder pressure and the pressure of the residual pulse combine their energy and the resulting pulse will be stronger than the pulse from the previous cycle. And the combined pulse from the next cycle will be stronger still, and so on; we have achieved true resonance.

Some may argue that we want a low pressure in the exhaust pipe when the port opens because then the spent gases will experience less resistance while leaving the cylinder. But that is not true. Gas flow depends on a pressure difference ratio. But once that ratio reaches 2, the flow velocity will reach Mach 1, the speed of sound. Raising the pressure difference any further will not raise the flow velocity any further.
The cylinder pressure at exhaust opening can be as high as 7 bar and the pressure of the reflected pulse will be about 2 bar. Thus the pressure ratio is well above 2, so lowering the pressure in the exhaust duct outside the cylinder will not do any good to the flow.

What has the exhaust timing got to do with the 'true resonance' I mentioned above?
The initial pulse starts moving at Exhaust Opening and it has to be back at Exhaust Closing, or a little earlier. This pulse travels with the speed of sound and its journey up and down the exhaust pipe will take t seconds.
The residual pulse starts moving at Exhaust Closing and it has to be back at the next Exhaust Opening. This pulse also travels with the speed of sound and its journey up and down the exhaust pipe will also take t seconds.
So from EO to EC takes t seconds and from EC to EO also takes t seconds. In English: the exhaust port should be open just as long as it should be closed.
Assuming that the crankshaft rotates with a uniform speed, this means that the crank angle during which the exhaust is open must be equal to the crank angle during which the port is closed. So both angles must be 180°.

I developed this line of thought some 40 years ago, but when I first published it in 1978 (in the motorcycle magazine Moto73 of which I was the technical editor) everybody called me crazy. Some people still do, but I got used to it .

Above I made a couple of assumptions. The crankshaft does not rotate with a uniform speed, but at high revs the deviation is negligible. In case you really want to know, I did the math for the Aprilia RSA125. At a nominal rpm of 13,000 the minimum rotation speed is 12970 rpm @ 107° after TDC and the maximum value is 13031 rpm @ 356° aTDC. What's more significant: the deviation in crankshaft position from truly uniform rotation is always less than 1°. So that really is negligible.

Second assumption: both the initial pulse and the residual pulse move with the speed of sound. Not true: the pulse pressures in exhaust waves are so high that acoustics rules do not apply any more. We are dealing with gas dynamics here and the stronger a pulse, the faster it moves. Since the residual pulse is weaker than the initial pulse, they move at different speeds. But we will leave this aside for now.

Third assumption: the initial pulse starts moving as soon as the exhaust port starts opening. More or less true, but we are not interested in the first weak appearance of the pulse; we want to know when the pulse reaches its maximum amplitude. And that requires a certain amount of open exhaust port area. It turns out that for our desired theoretical exhaust timing of 180° we will need a geometrical exhaust timing of about 190°, depending on the shape of the port: does it open gradually or does it open over its full width all at once.

The obvious question will be: why has the Aprilia RSA125 a geometrical exhaust timing of about 200°? True, at 190° the maximum torque value would be higher, but the engine would not want to rev because the blowdown time.area would be too small.
The 200° are a compromise: a bit less torque and a bit more revs; as long as the torque decline is smaller than the rpm rise, we gain horsepower.

Any sim you are using to design any part of a 2T engine, and dont take full account of the ignition timing regime - is a waste of time.
I can design a completely shit pipe, and with ignition tricks, make it work 1/2 way reasonable - in a sim and on the dyno.
But its impossible to design a really good pipe that will work well in reality, if you dont define exactly the ignition curve it will see when running.
You can change the temp in the header as seen by the egt probe, from 450 to 650C by simply taking away 4 degrees of timing when in the overev,so the pipe that before had a vertical power drop off
at 13500, now holds 50 + Hp out to 14500.
Same with having the solenoid powerjet scenario,you can easily make a pipe that will spin to 14,000 in the sim, but sadly it has no mid power to speak of at all.
Change the A/F ratio from 12:1 to 14:1 past torque peak, and a MUCH longer pipe, now has a ton of mid, then holds its torque up long enough for that " too long " TL to work at least another 1000 rpm than before,due to
the burning mixture now dumping a huge heat load out the port.

Cheers, I'd thought that would be the case based on what you have posted before.

It seems a little backwards designing the pipe to suit an ignition with a fixed curve shape but I'm going to have to go that way until I can afford to upgrade to an Ignitech or similar. That's going to have to wait for a long time though.
It would be great to able to change it but I have to make some compromises due to available resources.

Do you find the A/F ratio change in engmod close to reality? or do you just apply experience in that area?

Also I WILL be designing a completely shit pipe, relatively speaking, I just hope to get it less shit with the sim.

Using the Sim I've been able to compare different designs and I'm confident I can make more 'Simpower' than other pipes that I could be putting on the bike.
I would have thought the RG400 (I think it is anyway...) pipe I have on it now would be reasonably close but it appears miles off in practice and in the sim.

That is one thing about the 100 vs an Air Cooled 125; a random pipe of any old 125 seems to work OK compared to putting the same pipe on a 100.

You will spend more time and money friggin round with the old unknown ignition just over a longer period than biting the bullet for a programmable.
I went through this with suspension, spent countless hours rebuilding shocks, buying shims and seal heads. Finaly bought a set, bolted them on set the rebound and have not touched them since. They work 100 times better than my best efforts.

MOTA is a massive compromise especialy on the ignition side. However it will provide some useful info on the return wave timing which is what you should concentrate on. As Wob has said probably 100 times and it's worth repeating "big depression/lowest pressure at BDC" and return wave arriving before the exhaust port closes. Get that right then look to get the rpm peak where you want it, finaly jiggle the TL length %'s to what Wob has already posted. Viola no more shit pipe.

[wobbly]

I experimented with the B port rear wall hook when testing the BSL cylinders.
Honda at the time had a steep hook, but Aprilia and the cylinders from SA Design for the 500 GP flying web engine had smooth radi pointing to 1/2 way
between bore centre and the rear wall.
The smooth radi made better power up to the peak.
I also re-angled the front wall of the B port to perpendicular to the bore, as is done by Aprilia.
Although I didnt have the flat entry to the septum ( the angle changed smoothly down the duct ) this made more power everywhere.

[NAR RG500]

I experimented with the B port rear wall hook when testing the BSL cylinders.
Honda at the time had a steep hook, but Aprilia and the cylinders from SA Design for the 500 GP flying web engine had smooth radi pointing to 1/2 way
between bore centre and the rear wall.
The smooth radi made better power up to the peak.
I also re-angled the front wall of the B port to perpendicular to the bore, as is done by Aprilia.
Although I didnt have the flat entry to the septum ( the angle changed smoothly down the duct ) this made more power everywhere.

Hey Wobbly,

Sorry to Hijack thread but could you please PM me regarding RG cranks.

Thanks a lot,

Neil

[Muciek]

Guys I want to tune my engine right but I have few questions (Engine 70cc 44s x 45b 21mm carb reed valve ). How should I calculate window in cylinder for reed valve , and how big should be transfers from crankcase (I want to use 230* open inlet (power porting from bell book)).I heard about a ratio that area of the ports feed from crankcase should be 1.2/carb area (in my case it is 21mm carb 346,19mm2 area). But I have seen cylinders with much bigger windows and small carbs and it was working good. What should I do? Greetings

[chrisc]

http://www.motorcycle.com/manufactur...xp2-15170.html

Honda plan to campaign the EXP-2 again next year. The company says it has no plans to make a production engine right away, but from the success so far, we'd predict that the world's cleanest two stroke motorcycle will be in production before the year 2000.

Cough

[husaberg]

Cough

Blame Yamaha for that one with the YZ400F. Husaberg as well played a part

Honda have a long history of doing something grand just because they can. Corporate masturbation i guess.........

Look at the NR500 once Freddie (yes freddie was pretty special)proved it could be near competitive.It even won a non GP race against Kenny's Yamaha.(Luguna Seca 1981) So the next year they started building what they could/should have all a long.

[bucketracer]

Attachment 281897

The CVT has pretty much the same gear ratio range as the GP gear box.

So one possibility is to run the variator of a modified gear box input shaft and run the rear pulley on a shaft through the engine mounting plates with the front chain sprocket behind it. Effectivly replacing the GP's gearbox with the CVT.

TeeZee if you move the engine forward there looks to be plenty of room for the CVT.



With new shafts and the CVT you might even be able re arrange the GP gear box like this.

[FastFred]

How's this for a 2.5cc two/stroke doing over 300km/hr at 30,000 rpm?



and a 5cc 2/stroke breaking the world record - 335.8 km/h - insane rpms

[Frits Overmars]

While we're on the subject of record breaking: http://www.youtube.com/watch?v=FTmg1tq031A
Here's a 35,000 rpm MB40 engine doing a bit of radio-controlled(?) flight at over 400 kmh, breaking...every bone in the fuselage .

[husaberg]

While we're on the subject of record breaking: http://www.youtube.com/watch?v=FTmg1tq031A
Here's a 35,000 rpm MB40 engine doing a bit of radio-controlled(?) flight at over 400 kmh, breaking...every bone in the fuselage .

The warm up is a little brutal. how do the starters work direct onto the cone in front of the prop?
Any landing that the pilot can walk/run away from is a good one i guess.

[Frits Overmars]

The warm up is a little brutal. how do the starters work direct onto the cone in front of the prop?
Any landing that the pilot can walk/run away from is a good one i guess.

The starter motor has a countercone that is pushed against the model's prop spinner. It's as simple as that.
A friend of mine, ex-world champion F3D flying, has a day job as a Boeing 737-captain (" I'm a bus driver, but I get payed better").
According to this pro "Any landing from which the passengers can all walk away, is a successful landing. And if the plane is still usable afterwards, it was a véry successsful landing".

[RomeuPT]

I experimented with the B port rear wall hook when testing the BSL cylinders.
Honda at the time had a steep hook, but Aprilia and the cylinders from SA Design for the 500 GP flying web engine had smooth radi pointing to 1/2 way
between bore centre and the rear wall.
The smooth radi made better power up to the peak.
I also re-angled the front wall of the B port to perpendicular to the bore, as is done by Aprilia.
Although I didnt have the flat entry to the septum ( the angle changed smoothly down the duct ) this made more power everywhere.

Thanks for this info.

So, the type 2 angle is mostly like that, half way between bore center and rear wall.

Front wall of b-ports in the Honda cylinders are slighty aimed to the rear.

NSR and CRM cylinders came exacly with the Type-1 angle, both sides, maybe because they use 2 rings...

Were, some pics, Honda would arrest me if they were still on 2 strokes XD

A-Kit in picture 4!?

[dinamik2t]

Measuring the primary DC resistance of a coil does not tell you much about its inductance, burn time or the energy release.

A way of evaluating different coils is by measuring their stored energy.

http://www.dtec.net.au/Ignition Coil Energy Testing.htm

Ignition coil stored energy is measured in milli Joules (mJ) and is relatively easy to measure with some simple DIY equipment. Coil energy encompasses time, current and voltage characteristics. Stored energy is a very important factor, it relates directly to spark intensity and burn time. Very few people seem to realise how simple it is to measure and what an important aspect of an optimum ignition system it is, electrical engineers dealing with automotive ignition systems certainly do!
This tester does not measure coil voltage output of the coil, it is for measuring stored energy which, as stated, is extremely valuable information.

Has anybody used the setup described by Dtec to measure any coils/ignitons?

I am in the process of trying to extract some timing data from a cdi, but found a few difficulties, so I measured the coil energy along the way, which is simpler.
I set up a triggering arrangment with the porting motor (up to 15kRPM), a 2.5mm thick iron sheet, cut proportionately to the rotor's dimensions, and an SCR voltage regulator.

The thing is I measured an unexpected signal from the stock cdi, compared to Ignitech or the signal in Dtec's pdf. Second pic is Ignitech Race, third is a stock CDI.



Does this signal means there are minor "positive" and "negative" sparks after the first one?

Furthermore, energy seems low in comparison with Dtec value. The stock coil is ~0.5Ω Rprimary. Haven't tested a selettra and an RGV250 coil yet to compare.
Would anybody have any numbers from tests?

[speedpro]

The "stock CDI" doesn't lok like a CDI output. It looks like a standard Kettering or points/coil output. The oscillation is the coil resonating with the capacitor once the points open. Nowadays the points are replaced with a transistor but the principle is the same. The rise time of the voltage is a clue as well. CDIs are quick and kettering systems are slow which is why CDIs came along. The slow rise time of the voltage allowed time for energy leakage on a fouled plug. So much so on a badly fouled plug that the voltage never reached the point where it arced over before the coil ran out of energy.