ESE's works engine tuner

[koba]

For Transfers its Wobs or is it Frit's catch phrase, "wide and low" to get the specific blow down time area required (STA).

Somewhere else I read that low transfer ports work better than higher ones of the same STA.

The lower the transfer timing, the less risk of too-early returning exhaust pulses shoving the cylinder contents back into the crankcase.
In short: lower transfers give a better powerband, all other things being equal (which of course they never are).

Yah, it show very clearly in a wave function of MOTA how they are flowing the wrong way until almost BDC!

[TZ350]

Page 710 .... links list to go here.

Suzuki GP125 and GP125U service manual... all 136 pages of it. It's a large file (for those who still use windows 98) at 18.0 MB

Suzuki GP125 Service Manual

Crank Case Volume

Most of the volume is concentrated in the transfer ducts. Then there is the volume inside the piston of course, and the 1 mm shear-avoiding clearance at all surfaces of the crank.

But that is not nearly enough volume. If you take another look at the Aprilia crank below left, you will notice that the space between the crank webs is the same as the space needed for the big end bearing.



In other words: the crank webs have flat insides, good for another 60 cc or so, if I remember correctly.
Additional benefits: the con rod has an easier time pushing the mixture aside as it moves between the webs, and the big end bearing gets a lot more cooling and lubrication because it is not shrouded in any way.

Because there are no overhung bobweights, the crank webs are stuffed with tungsten to get the balance factor right. In the RSA125, the con rod was lengthened from the RSW's 115 mm to 120 mm to create even more crankcase volume.

The paddling is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture.

Smooth, full-circle crank webs have the advantage that there is little mixture hiding in nooks and crannies. An example of it's importance: in a certain engine there were 20 mm spaces between the crankshaft bearings and the seals. these ill-accessible volumes acted as pneumatic dampers on the crankcase pressure fluctuation. Filling those volumes with plastic bushes gave a measurable improvement.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

The picture right below shows, wait for it, an RSA125-crank with stuffers...



After Jan Thiel went into retirement in 2008, some geniuses at the factory grabbed their chance to 'correct' the errors that Jan left behind, without even testing the result because 'everybody knows the smaller the crankcase volume the better'. But they never could understand why a 2011 RSA125 was slower than a 2007 model (just look at the 125 cc top speeds on any GP-track). O, the joy of working with Italians.....

The Red line is the smaller crank with 2mm clearance. I am not sure why the improvement is all at the bottom end and drops of earlier at the top.

Helmholtz frequency, my dear Watson. The smaller crank will give the pipe more crankcase volume to breathe from. This larger volume will also lower the resonance frequency of the inlet system, hence the drop at high rpm. It can be compensated with a shorter inlet tract, a bigger carb diameter and a later inlet closure. To put it real simple: if you have more volume, you need more time to fill it. But more time, i.e. later closure, has adverse effects at low revs. So my preference is a shorter tract (unless you go the 24/7-way and employ a reed for the low revs, and swing it out of the way at high revs).

To put it real simple: if you have more volume, you need more time to fill it.

Specific Time Area explained in 12 words. It's not yet as short as E=mc² , but I'm working on it.

so if TZ is working with a 24mm carb restriction he has likely found the limit of crankcase volume.

You're welcome, Dave.To the superficial reader that would seem as if the crankcase volume was too large. I would prefer to formulate it like this: TZ350's combination of crankcase volume, inlet tract length, inlet diameter and inlet timing is running out of breath at high revs.
I would rather shorten the tract, increase the diameter (if allowed) or lengthen the timing, in that order, and preserve (or even enlarge) the crankcase volume.

For example , the proven need for huge case vol in a full house race rotary valve engine, isnt even close to being a positive element in a stocker reed valve engine with seriously crap transfer ducts.

Quite the opposite will produce better power in that scenario.
The smaller case vol gets the flow going sooner and more effeciently when the duct geometry is compromised , but then of course peak power cant be the object of the end game, with that upsetting mechanical limitation.

Flowing the wrong way between Transfer Open and BDC is not the result of a too-early returning exhaust pulse, but of insufficient blowdown time.area.

What I meant was the instant just before Transfer Closure. The stuffing pulse from the exhaust should not arrive at the cylinder just yet, but at rpms under the powerband it will, raising the pressure in the cylinder while the transfers are still open.

So the fresh charge gets pushed back into the crankcase, leaving little of it in the cylinder. And on top of that, just after the transfers close, that stuffing pulse reverses sign and direction, and sucks what little charge is left in the cylinder, out...

Loss of heat should be avoided all right, but if you want power, it is more important to avoid detonation. The part of the exhaust duct where washed-through fresh charge temporarily resides, should be kept cool to avoid heating up that charge.

And it is much simpler watercooling an exhaust duct that is part of the cylinder, than cooling a duct that is part of the pipe.....

The det amp is very selective about displaying real deto signals.
You simply wind in the sensitivity such that the two greens are on and then the orange will tell you where you are getting close
to a knock.
Wind up the sensitivity again and the red will come on in the same spot as the orange did before.
Pull out a degree or two at that rpm and the red will go out - leaving the orange semi warning.
Keep doing this till the curve is optimised.
It works the other way as well, no orange and you can be sure you dont have enough advance at that point.
Then you can run the earth line back to the Ignitech with only one or two degrees of deto retard a a failsafe.
If you try to run say 3* of retard with the sensor output connected to the Ignitech, it works so fast the light never comes on, so you cant see whats happening.

P558

The shock waves from deto will be transmitted right thru the cylinder and the case.
I have seen many times where for no apparent reason the head or barrel studs loosen off - not because they weren't torqued correctly, but due to the
gasket being crushed momentarily from deto.
Many cars have the det sensors on the side of the block, some with multiple sensors for cylinder pairs.
All that happens when the sensor is further away from the chamber is that the shock intensity is reduced, so the sensitivity of the amp must be wound up - not an issue.

P559

Lambda is not a reliable tool for any length of time in a 2T.
The heated ones last a bit longer but no matter what probe type is used they get contaminated and don’t read correctly in a very short time frame.
EGT is very simple. If you find peak power at say 1240* ,and know what the RAD was on the dyno, then its easy to construct a jetting pattern.
Every 3% rad = 1 jet size in a Kehin or Dellorto that use metric sized jet holes.
Always start on the rich side and jet down to the set EGT.
Best example I can give was at Vegas World Kart Champs.
In practice we went down one or two jets every run - as long as we saw a temp rise around 50* per jet,and the ground strap mark was clean at 3/4 length, then we were making more power.
At RAD 101 we had 1260, going one more only raised egt about 20* so NFG going there.
This was a 162 jet before we changed.
On qualifying morning it was cool and RAD104 - up one jet to 165 and we saw 1255 - on the money, qualified 2nd by 0.003 sec.
First race after lunch was RAD98, down 2 jets, won the first heat easily and saw 1265* and immediately were accused of cheating, for blitzing the Yank Champ down the shute..
He hadn’t jetted down enough for the hot afternoon RAD change.
Its that simple, once you have a baseline.
You can use the egt and the CHT as well, but that’s another story.

Have tried the remote hose to the Lambda thing and although the probe lasted better it was slow responding.to the extent that it is impossible to log the Lambda
output against rpm/Hp on the printout.
The reading I think was about 2000 rpm behind the engine when accelerating at 300 rpm/sec.
Dynojet has an expensive add on kit that uses a pump to draw the gas thru a tube that goes in the muffler, this has a filter element in it so should make the probe reliable.
But it doesnt work on a 2T - even apart from having something affecting the test by altering the outlet area of the muffler itself..
I have seen one Dynojet session where the customer had to pay for 2 probes in a 4 hour test cycle. NFG.

Re using EGT and CHT.
The only probes that are worth shit come from Exhaust Gas Technologies.They guarantee them for 2 years,and I have had no problems since changing to them.
They sell probes to Nascar/IRL/F1/MotoGP teams with a guarantee - the only guys to do this with exposed tip,high speed temp sensors.
The company sells Digatron gauges on Ebay,and having just started to use one with 2 screens and 5 functions - im sold.
The ones sold by Mychron etc for kart use are crap, seen several brand new setup last two laps.

Using the two gauges together,especially if you have say a Digitron data logging gauge,makes jetting much easyer.
Basically when the jets are rich, both egt and cht will rise then fall together,when doing a full throttle all gear run.
You can keep dropping jets and be sure that all is well as long as they both rise together - with the one caveat I stated above.
One Keihin main jet size should lift the egt around 50*F, if you only get 20* rise from a previous jet then what is happening is this.
There is only "x" amount of energy in the fuel ingested.This can end up in the trapped,expanding gas - making power.
It can end up in the water, via the head and cylinder wall,and depending upon the com or ignition point,alot simply exits the port and heats up the pipe.
BUT - as soon as you go overly lean,the combustion pressure/temp gets to a point where instead of heating the combustion charge, the flame front starts creating free radicals.
This uses a huge amount of the available energy,and instantly the egt drops.
Once free radicals have formed,they keep the process going,causing destructive deto to get worse and worse - thus the egt drops thru the floor.
You need exposed tip,fast probes to see this quick enough to save the engine.

Thus on the gauge,the CHT keeps rising fast,but the EGT slows and can drop down again.
In the above example I gave, the egt only rising 20*F pointed instantly to the fact that we were approaching deto point.
By watching the two temps track upwards together it is real easy to get a handle on what the engine wants, to make peak power - just short of deto.

CHT is dead accurate on a watercooled head as far as the rising temp is concerned.
The washer reads the heat load into the plug,its a bit slower than on an air cooled engine but the data is still valid.
More important is the fast response needed for EGT tracking,so you see immediately the temp slowing and then dropping when deto sets in.

The A/F meter is no different than the Lamda readout - the sensor soon dies due to contamination of the sensing surface.NFG.

The last injection setup I worked on we built an interface for the ECU that converted the EGT reading to the Lambda scale that the computer recognised.
This worked well on a Jetski setup,that is usuall all go or none.

Welp, I guess it is about time I contribute something to this forum...

Don't want to step on Wob's toes, but...

I have used a lot of the data loggers that are available (Motec, Aim, Digatron, Pi, CDS, Racepak) and...

The Mychron is a good starter setup, but if you decide to go beyond the basic logger and GPS, expansions are expensive and limited. I outgrew mine in a year... Most of the issues like Wob mentioned are actually just due to poor leads: user setup, and not properly strain relieved, yellow tc connectors not tight (yeah they come from the factory like that..) Easily fixed before you install with some silicone and shrink tubing. You don't have to have the Digatron to use the good open tip EGT's Wob mentioned, any logger with k-type will work. (And Yes, the open tip E.G.T. egt probes are as good as Wob says)

The best bang for your buck, full on data logging is without a doubt the AIM Evo4 (same guys as Mychron). Comes with the GPS, and has virtually unlimited expandability (number of channels). The best part is you can run whatever sensor your heart desires or can dream up (differential pressure for aero, ultrasonic distance, tire temps etc.) Price is close to the Mychron, gps, and an expansion module! And AIM has the most user friendly software I have used. If you want to get beyond the 3 basic temps, this is the ticket. Great stuff.

The only thing better is a full on Motec system, awesome stuff but WAY out of the price range for the average racer.

Haven't personally sorted out the lambda completely yet (only run it twice), but they can work, the snowmobile guys have been using them successfully for years. What I have learned so far is keep the pipe temp up and engine clean so the sensor temp can stay up and not foul. If it sees a real rich condition for an extended period of time (like warming up engine for dyno run maybe?) you'll have issues.

The issue that your test doesn't address is that with pump gas you may be able to get away with 13:1 com.
With AvGas its just starting to work properly at 15:1 and this attribute will always far outweigh any advantage flame speed or whatever may be contributing from the pump gas scenario.

The other issue is that unleaded fuel works best with plenty of advance, no com, and rich as hell.
AvGas loves com, loves running lean and hates advance, so you need to spend days on the dyno just optimising for the fuel.
Much better things to be doing in making a fast reliable race engine I believe.

Robinsons book offers a nice little piece on optimising fuel, ignition and comp to suit different fuels using a variety of fuels, but i guess you already knew that



http://books.google.co.nz/books?id=8...onepage&q=john robinson two stroke tuning optimising fuels&f=false

http://www.tmkpackers.co.nz/index.php/site/product/acetone

Husa IPA (Isopropyl alcohol) is used to make Hash

PWM control of the powerjet is a very sexy use of technology,slowly ramping off the fuel flow against rpm, but in reality using a simple rpm controlled switched solenoid work perfectly fine.
Yamaha and Honda have used the switched powerjet since forever, its reliable and does the job.
Only issue you need to address is the jet size and switch point ( along with TPS value ).
Running Avgas as we are still allowed to do, means that the tuning is based around getting high egt numbers to create good power, with lots of com and advance - unleaded is the opposite..
Thus experience has shown that as leaded fuel works best with a lean condition at peak power, we only need to switch a small jet just past peak - to increase the pipe temp and
thus give better overev.
In the Keihin numbering this is in mm dia and switching off a .35 is perfect.
When running unleaded, as the GP bikes have for years, the fuel likes to be rich at peak to create the best power, thus we need to switch off alot of fuel flow to increase the pipe heat quickly enough.
In this case a .65 is needed to do the job.
On the dyno or on the track it is easy to tell if the switch point is a little too low, as it feels exactly like the bike has changed into another gear past 6th.
It jumps forward when the solenoid kicks in - making the fuel curve lean, too early.Do this enough - and bang.
Its critical to 100rpm, and is working perfectly when you dont feel it happen - the power just keeps going.
To do it on the dyno you have to run the bike in 6th to simulate the acceleration rate as seen in that gear on the track, and is easy to do running back to back run ups.
Changing the rpm number 100 at a time, lower in the Ignitech, reprogram on the fly and run again.
If the rpm is too high - nothing happens, as there isnt time for the heat to affect the pipe wave speed.

I was wondering about setting up the powderjet jetting. I have the Kehin solenoid powderjet modded the way you showed on this thread and the .35 jet recommented but because of other issues with my bucket I blocked it off with a soldered up jet and tuned it up as a nomal carb. Now say I used a 1.60 main jet on the nomal carb then I add the powderjet is it 1.60 main jet minus .35 powderjet = 1.25 main jet is that right?

Yep Mitre 10 is the simple answer to easy access to Acetone.
About a cup full in 5L does the job in AvGas.

Re the powerjet sizing the answer is NO NO NO.
Cant be bothered now but work out the AREA of a 160 main and subtract the AREA of a 0.35 powerjet.

Area 1.6 main = 2.010, less area 0.35 = 0.0962.
Main jet should now be 1.56,closest is 1.55 with the powerjet .
Try this without switching first to check equivalent egt to original setup.

EGT is very simple.If you find peak power at say 1240* ,and know what the RAD was on the dyno,then its easy to construct a jetting pattern. Every 3% rad = 1 jet size in a Kehin or Dellorto that use metric sized jet holes.
Always start on the rich side and jet down to the set EGT.

In practice we went down one or two jets every run - as long as we saw a temp rise around 50* per jet,and the ground strap mark was clean at 3/4 length, then we were making more power.
At RAD 101 we had 1260, going one more only raised egt about 20* so NFG going there.
This was a 162 jet before we changed.

On qualifying morning it was cool and RAD104 - up one jet to 165 and we saw 1255 - on the money, qualified 2nd by 0.003 sec.

First race after lunch was RAD98, down 2 jets, won the first heat easily and saw 1265* and immediately were accused of cheating,for blitzing the Yank Champ down the shute..
He hadnt jetted down enough for the hot afternoon RAD change.
Its that simple,once you have a baseline.
You can use the egt and the CHT as well, but thats another story.

Great description, but I'm a little confused. So on the dyno you saw 1240deg at peak power. I would have thought at that time you would err on the lower side of the temp.

But are you saying that that calibrates the guage & you try get close to that & then keep goin up until it stops rising linear for that final bit?

At this stage presumably if you have a det guage or counter you could get away from needing a CHT perhaps?

In answer to your question Dave.
Matters not how the best temp was derived,on track or on the dyno.
With the gauge running and say a 180 main,then going down to 178,if I only see a small increase in temp ( 20*F) then that instantly means
that more heat energy is being used somewhere - not in heating the Ex gas to make power.
If the original temp was 1240, then that will be the ref temp for any air conditions on any day.
With the example I gave we had a 3 jet spread during the day, a very cool dense morning,and a very hot dry afternoon.
In both cases the egt settled at around the same mark.One jet leaner and we would be in the danger zone - one richer and we wouldnt be the fastest by a mile as we were.

My new digatron data logger just arrived! Any specific tips for tuning with egt and cht? Ive read as much as I can find but if anyone has any words of wisdom I'm all ears...

Have tried the remote hose to the Lambda thing and although the probe lasted better it was slow responding.to the extent that it is impossible to log the Lambda
output against rpm/Hp on the printout.
The reading I think was about 2000 rpm behind the engine when accelerating at 300 rpm/sec.
Dynojet has an expensive add on kit that uses a pump to draw the gas thru a tube that goes in the muffler, this has a filter element in it so should make the probe reliable.
But it doesnt work on a 2T - even apart from having something affecting the test by altering the outlet area of the muffler itself..
I have seen one Dynojet session where the customer had to pay for 2 probes in a 4 hour test cycle. NFG.

Re using EGT and CHT.
The only probes that are worth shit come from Exhaust Gas Technologies.They guarantee them for 2 years,and I have had no problems since changing to them.
They sell probes to Nascar/IRL/F1/MotoGP teams with a guarantee - the only guys to do this with exposed tip,high speed temp sensors.
The company sells Digatron gauges on Ebay,and having just started to use one with 2 screens and 5 functions - im sold.
The ones sold by Mychron etc for kart use are crap, seen several brand new setup last two laps.

Using the two gauges together,especially if you have say a Digitron data logging gauge,makes jetting much easyer.
Basically when the jets are rich, both egt and cht will rise then fall together,when doing a full throttle all gear run.
You can keep dropping jets and be sure that all is well as long as they both rise together - with the one caveat I stated above.
One Keihin main jet size should lift the egt around 50*F, if you only get 20* rise from a previous jet then what is happening is this.
There is only "x" amount of energy in the fuel ingested.This can end up in the trapped,expanding gas - making power.
It can end up in the water, via the head and cylinder wall,and depending upon the com or ignition point,alot simply exits the port and heats up the pipe.
BUT - as soon as you go overly lean,the combustion pressure/temp gets to a point where instead of heating the combustion charge, the flame front starts creating free radicals.
This uses a huge amount of the available energy,and instantly the egt drops.
Once free radicals have formed,they keep the process going,causing destructive deto to get worse and worse - thus the egt drops thru the floor.
You need exposed tip,fast probes to see this quick enough to save the engine.

Thus on the gauge,the CHT keeps rising fast,but the EGT slows and can drop down again.
In the above example I gave, the egt only rising 20*F pointed instantly to the fact that we were approaching deto point.
By watching the two temps track upwards together it is real easy to get a handle on what the engine wants, to make peak power - just short of deto.

Page 562

CHT is dead accurate on a watercooled head as far as the rising temp is concerned.
The washer reads the heat load into the plug,its a bit slower than on an air cooled engine but the data is still valid.
More important is the fast response needed for EGT tracking,so you see immediately the temp slowing and then dropping when deto sets in.

The A/F meter is no different than the Lamda readout - the sensor soon dies due to contamination of the sensing surface.NFG.

The last injection setup I worked on we built an interface for the ECU that converted the EGT reading to the Lambda scale that the computer recognised.
This worked well on a Jetski setup,that is usuall all go or none.

Each engine is different but if a setup has the optimum com and the timing in the ballpark of 15* at peak power,then Avgas or leaded racegas around the equivelant RON
will always be maxed out at around 1250* - @ 150mm min from the port.
Unleaded likes to be alot richer and makes more power with more advance so that setup makes best power at around 1050.
Not enough com or advance, and the peak safe egt will rise, but power wont,it will just rev on more due to the higher wave speed.
But you have still got it wrong about the air on the day.
You can jet to get the optimum egt,no matter what the RAD says,and it will be in the same state of tune - just using all the oxygen in the air available and mixing it with the correct amount of fuel.
On a hot day,or low Baro, it will hit 1250 but simply make less power, due to less oxy and thus less fuel = less BTUs burned.

The 400 F3 we thrashed on the dyno and at 12,000 held by the dyno for around 30 secs it settled at 12000* F - 96 Hp with no fade.
Thus this is a good safe baseline for the new owner who may not have the tuning smarts to determine what is good or not - but if he has to change jets 3 times during a day
to see 1200 then he will be well on the way to learning what to do.

A whole bunch of interesting links on Bucketracers post.

Page 520 .... the last ten pages were mostly about what some wheels weigh, ATAC valves and crank stuffers.

[TZ350]

Yah, it show very clearly in a wave function of MOTA how they are flowing the wrong way until almost BDC!

I love engine development simulators....... ... and what you can learn from them.

[teriks]

Here it is: the MB40-6port. What is your link with MB40 engines, Teriks? Do you take part in F3D competition? If so, under which name?

Thanks for the picture Frits, newer saw it in person, only spoke with Rob about it.
Name's Thomas Eriksson, if you cut a few letters here end there you end up with teriks
I have been using Robs engines since 1999, was more active in F3D up till 2006 when priorities somehow changed a bit. Could be linked to getting a kid, house and change of work maybe?
At the moment I'm fiddling with a RI crankcase for the MB40-LS top end on the CAD. Ended up being a very long term project, but getting there. Next challenge is to get the parts manufactured.

//Thomas

[husaberg]

The lower the transfer timing, the less risk of too-early returning exhaust pulses shoving the cylinder contents back into the crankcase.
In short: lower transfers give a better powerband, all other things being equal (which of course they never are).

Yah, it show very clearly in a wave function of MOTA how they are flowing the wrong way until almost BDC!

I love engine development simulators....... ... and what they can tell you.

This is some extensive full use of the available width (off pitlane first) but i never noticed it in the Jan and Frits thread before?

Jan Thiel Remember one thing of all the ports the transfer ports are open the shortest time.
And the quantity of air which it is intended is a good engine over the cylinder!
The speed must be high, it can not be otherwise.

That the flow bench is another story.
It turned out that most of the flow does not always give the most power.
The transfer currents 'collide' and inhibit each other that way.
Otherwise everything would go directly into the exhaust.
Also, the transfer ports wider, towards the outlet, gives a lot more flow.
But less power ......(i hope i translated that right husaberg)

Jan Thiel What preliminary conclusions about MOTA engine simulation.
There are a few strange things.

You also have the choice between a do, and not 'water-cooled' outlet.
Water-cooled means a well chilled, surrounded by water, exhaust duct.
The "engine" runs a 'chilled' exhaust duct much worse.
This is in stark contrast to what I practice seen.
The better we cooled exhaust duct, the more power and less detonation, very clear.

Plus as always a question For Mr Overmars.

I have always thought the exhaust duct is to be kept as short and as possible to limit he loss of heat? i are clearly wrong (obviously).
But why is this often repeated? Am i confussing volume with length i see the RSA was CNC'ed i guess to ensure it was exactly as per spec

[Haufen]

just stumbled upon this searching my library. I've got the whole paper, too, but the board won't let me upload it because it's bigger than 1mb.

thats a rather old paper though, with todays more modern combustion chamber shapes and squish areas, things might have changed. but the tendency should remain the same.

[gamma500]

Here you go, TeeZee: 'small' engines, turbo, nitro and pulleys. The pulley transmission keeps up fairly well with the engine power, wouldn't you say?
http://www.youtube.com/radarruns

I almost forgot: the indicated speeds are mph .

Do you have more pics and info of that sled? What kind of fuel system does that monster use?

[F5 Dave]

just stumbled upon this searching my library. I've got the whole paper, too, but the board won't let me upload it because it's bigger than 1mb.

thats a rather old paper though, with todays more modern combustion chamber shapes and squish areas, things might have changed. but the tendency should remain the same.

ok so I wonder how one would test for that. Just on the dyno? Clearly you would have case heating added to the equation causing the initial drop off.

Drag race 2 strokes they don't always run with water as there's no point.

But here's the thing. I often find, & like my dirtbike is a prime example, but I see it on the dyno as well; the first run through a gear doesn't pull smooth. I don't think its loading up, or maybe it only loads up with cold cases, but after throwing it a run or two through the gears, its sweet.

It doesn't matter a damn, but it is curious. I'd just assumed its too cold. But the graph above suggests otherwise.

[Flettner]

Just trying to learn how this forum works.
Now I see how videos are posted!

[Frits Overmars]

The lower the transfer timing, the less risk of too-early returning exhaust pulses shoving the cylinder contents back into the crankcase. In short: lower transfers give a better powerband, all other things being equal (which of course they never are).

Yah, it show very clearly in a wave function of MOTA how they are flowing the wrong way until almost BDC!

Flowing the wrong way between Transfer Open and BDC is not the result of a too-early returning exhaust pulse, but of insufficient blowdown time.area.
What I meant was the instant just before Transfer Closure. The stuffing pulse from the exhaust should not arrive at the cylinder just yet, but at rpms under the powerband it will, raising the pressure in the cylinder while the transfers are still open. So the fresh charge gets pushed back into the crankcase, leaving little of it in the cylinder. And on top of that, just after the transfers close, that stuffing pulse reverses sign and direction, and sucks what little charge is left in the cylinder, out...

At the moment I'm fiddling with a RI crankcase for the MB40-LS top end on the CAD. Ended up being a very long term project, but getting there. Next challenge is to get the parts manufactured.

Did you talk to Rob about it, Thomas? To my knowledge he did not plan production of Rear Intake crankcases for the MB40 LongStroke, but he is an extremely flexible person and as he has all the necessary tools, templates and moulds, it would turn out to be a lot cheaper if he would produce those parts himself.

I have always thought the exhaust duct is to be kept as short and as possible to limit he loss of heat? i are clearly wrong (obviously). But why is this often repeated?

Loss of heat should be avoided all right, but if you want power, it is more important to avoid detonation. The part of the exhaust duct where washed-through fresh charge temporarily resides, should be kept cool to avoid heating up that charge. And it is much simpler watercooling an exhaust duct that is part of the cylinder, than cooling a duct that is part of the pipe.

Why are mistakes often repeated? Good question. Humanity and civilization would be a lot better off without that. We are probably simply not bright enough to recognize errors the first time they occur. But let's not get too philosophical yet; it's only monday morning here....

[teriks]

Did you talk to Rob about it, Thomas? To my knowledge he did not plan production of Rear Intake crankcases for the MB40 LongStroke, but he is an extremely flexible person and as he has all the necessary tools, templates and moulds, it would turn out to be a lot cheaper if he would produce those parts himself.

I did, a long time ago when I first started this project. Now I think my timing is kind of bad, my guess is that he's even more busy than normal, with the WC on home soil and all.
Actually I have found someone close by with a good workshop, who is also interested in these kind of things. Might not get too expensive for a few prototypes, but as with most skilled people, he's also very busy.

Guess I'll repeat a few of his past mistakes instead, and probably add a few of my own.

[TZ350]

How to shorten a big end pin needed for a crank rebuild, just cut it off with a slitting blade, works a treat.

[husaberg]

Loss of heat should be avoided all right, but if you want power, it is more important to avoid detonation. The part of the exhaust duct where washed-through fresh charge temporarily resides, should be kept cool to avoid heating up that charge. And it is much simpler watercooling an exhaust duct that is part of the cylinder, than cooling a duct that is part of the pipe.

Why are mistakes often repeated? Good question. Humanity and civilization would be a lot better off without that. We are probably simply not bright enough to recognize errors the first time they occur. But let's not get too philosophical yet; it's only monday morning here....

I guess i deserved that with such an open ended question.

I do recall Mr Frits saying if we are good we might see some more of the "Frits files"
Om some non Aprilia engines

[koba]

Flowing the wrong way between Transfer Open and BDC is not the result of a too-early returning exhaust pulse, but of insufficient blowdown time.area.
What I meant was the instant just before Transfer Closure. The stuffing pulse from the exhaust should not arrive at the cylinder just yet, but at rpms under the powerband it will, raising the pressure in the cylinder while the transfers are still open. So the fresh charge gets pushed back into the crankcase, leaving little of it in the cylinder. And on top of that, just after the transfers close, that stuffing pulse reverses sign and direction, and sucks what little charge is left in the cylinder, out...

Ahh, right, yes.
I'm starting to understand all this a bit better.

I plan to spend a while playing with the return pulse and seeing how pipe changes affect it's characteristics.
The next pipe I make will take this into greater consideration.
The current one is far from perfect but I'm quite happy with it for a first stab (so far).
I'm sure more study and experience will bear sweeter fruit.

The inadequate blowdown is the aspect that shocked me when I saw it in the SIM, even on simulations of competition engines with large blowdown area the eruption down the transfers is quite graphic!

[koba]

How to shorten a big end pin needed for a crank rebuild, just cut it off with a slitting blade, works a treat.

Good to see the lathe bed protected from that nasty abrasive shit!