ESE's works engine tuner

[wobbly]

This is the perfect time for me to step in and tell you to stop dreaming.
40Hp at 9,000 for a 125cc engine = 16Bar = 230 psi bmep.
ABSOLUTELY IMPOSSIBLE, NEVER BEEN EVEN REMOTELY APPROACHED, AND NEVER WILL BE.
New Years Wake Up Call.

[richban]

What are you doing for fun over the Christmas Holidays ..........

Similar stuff. I am designing and building new headers to try find that happy place. Will be interesting to see where it ends up.

[TZ350]

You beat me to it by a little bit.

40Hp at 9,000 for a 125cc engine = 16Bar = 230 psi bmep. ABSOLUTELY IMPOSSIBLE ...

Yes I understand that, but 36 crank hp at 12K is 11 bar and thats possible, I have been close to that already.

Its that the ports for 36hp at 12K are big enough for an impossible 40 at 9 and this suggests some sort of power valve arrangement on the ports could be good.

The objective is to get the highest torqe we can at 9k and finish with 36 crank hp at 12k.

Basically the torqe curve peaks at 9 and the power curve runs flat to 12 as the torque curve declines.

I have no idea of whats possible but I will find out what can be done as the design process develops.



36 crank hp at 12,000 rpm requires 11 bar, Been there done that, or at least close.



36 crank hp at 9,000 rpm requires 14+ bar, possible but difficult and maybe not thermaly possible for an air cooled motor.

At least I now where I have to go in chamber design, peaky Road Race at 9K.

[ief]

Shouldn't you work the other way around i.e. make optimum setup for 36 hp @ 12 k and then use the trombone to gain torque below?

Otherwise torque will fall of after 9 k, would that be driveable? (if doable at all)

[TZ350]

Shouldn't you work the other way around i.e. make optimum setup for 36 hp @ 12 k and then use the trombone to gain torque below?

Yes I thought so too, but in my EngMod2T simulations I always found it worked best to shorten the pipe and carry the power on.

Shortening the pipe also kept the vital header and diffuser length percentages within range for longer.

Lengthening the pipe did not work so well.

Thats why I want to start at 9 and carry on to 12.

Otherwise torque will fall of after 9 k, would that be driveable? (if doable at all)

Yes, the torque will fall off as the rpm goes up, thats how its possible to get a flat power curve. Will that be drivable, I think so.

I have seen flat power curves on dyno graphs, so it can be done, can I do it???? maybe.

[husaberg]

Yes I thought so too, but in my EngMod2T simulations I always found it worked best to shorten the pipe and carry the power on.

Shortening the pipe also kept the vital header and diffuser length percentages within range for longer.

Lengthening the pipe did not work so well.

Thats why I want to start at 9 and carry on to 12.

I thought, though likely wrong that the trombone shortens to gain over rev.Rather than lengthens to gain low end power???????
i certainly are no expert but it took me a while to get my head around that it may be better to first aim for the peak that you want.
(This is two strokes in general) i think it came from Wob or Frits, when i asked about trying to spread the power by tuning say inlet to a sightly different rev than say exhaust
it was said that it was better to use cunning tricks like solenoid carbs and ignition tricks and maybe a trombone pipe to spread the power by increasing the over-rev. rather than using other methods to broaden the power down low. but i am pretty sure this is a half quote probably out of context.........

[Farmaken]

I was playing with Mota just yesterday trying a very basic trombone/ATAC sim

Used a pipe that gave good top end and over-rev and added 100mm to the header length to represent the ATAC chamber or extended trombone header

Long header fattened up the bottom end/mid from 7k and fell over at about 10k - shorter pipe makes max power at 12500

If I was less of a computer retard I would post the graphs

[TZ350]

I thought, though likely wrong that the trombone shortens to gain over rev. Rather than lengthens to gain low end power???????

Yes, the Trombone that Frits showed us went both ways, but its about keeping things in resonance and we know from Frits that 190 deg exhaust duration is the target number.

(190 . 192 ex duration???? I will have to find the original post to confirm the exact number Frits said.)

But if your short on blow down STA, although its not ideal, you might have to increase the exhaust duration even though around 190 works the best at keeping the pipe in strong resonance. So exhaust duration becomes another trade off.

As I understand it .....

(1) 190 deg Ex duration is the magic number regardless of rpm.

(2) To remain in resonance the pipe shortens as rpm goes up.

So by dynamically changing the pipes length you can keep it in resonance with the exhaust port as the rpm changes.

From running a few EngMod2T simulations I have formed the idea that a Trombone style pipe gives a better result being shortened than lengthened.

I think thats because shortening the pipe also kept the vital header and diffuser length percentages within range for longer than lengthening the pipe seemed to do.

That is why I want to start at 9k and run out to 12.

[husaberg]

That Dutch trombone pipe moved from +70 mm length to -20 mm length, so its effect was concentrated on the lower revs (although raising max.rpm from 14,500 to over 17,000 rpm was a welcome bonus).

oh got that wrong more than usual.......
can't find the post either ROB but found these.........

Thanks Frits for your answer about the 180 deg port duration.

Attachment 262139

Here is a simulation of the Trombone effect. Datum is at 14500 and it went -30mm and extended +45mm, for a total slide movement of 75mm. Seems to be more more of an effect at peak power than at the lower revs.

Its a very interesting idea, being able to extend the power peak like that .... now what could I do with that

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.

We would get by with 6 gears like we did in the 125 cc class until Dorna killed it last year. Don't be misled by the Aprilia's power valves. They were there because the same cylinders had to be used on the 250 twins, which would have been too vicious without them. The 125s did not really need them. And having many gears to cope with is a big disadvantage. Not only does each gearshift interrupt the power, bringing unwanted movement in the bike and distracting the rider, it also interrupts the gas dynamic processes in the engine which means full power won't be available right after each shift.

Francis Payart's answer makes perfect sense. Besides, he should know, he bought the winning Aprilia RSA125 right after the last 125 cc Grand Prix and today he produces his own, very well-made copies of those cylinders for his 250 cc tandem twin FPE superkart engine.
The port in the cylinder casting has a timing of 196°. Then the upper edge receives a radius that lifts the timing edge to 202°. It's as simple as that.

With a variable header length you do not need to artificially raise the exhaust gas temperature, so you need neither the power jet nor the ignition retard.
The 50 cc engine with trombone pipe that I wrote about some time ago, runs strongly from 7,000 to 17,000 rpm without power jet and ignition retard.

Note: the power jet in the Aprilia RSW / RSA is gradually closed and the ignition is gradually retarded till 10° before TDC. These engines rev to 14,500 rpm. But I am convinced that with a trombone pipe they would function much better still.

Thanks for the flowers, RAW.
You can have an intake length that is too short in combination with intake diameter, intake timing, crankcase volume and desired rpm, in which case the engine will express its displeasure by blowing back some of the inhaled mixture. I prefer to shorten the intake length as much as possible and shorten the intake timing accordingly.
By varying intake length, intake timing or crankcase volume you can adapt the induction system to different rpms. I think the best way to adapt to low revs is to advance the intake closing; it will make for a docile engine with a clean, easy to set carburation.

Varying exhaust pipe length seems to be a far better way of increasing overrev than retarding the ignition or leaning out the mixture; it would be a waste not to utilize all inhaled oxygen. Varying the pipe length can also markedly lower the beginning of the power band.

[TZ350]

Thanks Husa, all good stuff .....

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.

This bit talks about the optimal 190 deg exhaust duration and the blow down compromise.

[TZ350]

This is an old graph but it shows how a pipe that peaked at 10,500rpm can be made to extend the power curve by progressivly shortening it. Although -130mm might be a bit much in mechanical reality.

I want to start about 9k and finish at 12 ish with 30 rwhp. And to do that I need the ports STA's to be right at 12 but they are obviously over sized at 9, we will just have to find a way to live with that.

[TZ350]

Page 680 all ready ...... some more of those pipe posts from Wob and Frits to go here when I sort them out.

With todays technology the bar can now be raised to around 40 crank Hp without too much drama involved, and thus achieving around 35 RWHp.
Its just a matter of careful parts selection and very careful assembly.

The alloy inserts for the TZ350 was the customers choice - once its all proven, and we get a handle on what the engine likes, then I will do some bronze ones.

AvGas in NZ is all LL100, this is low lead 100 octain.But the rating is defined differently in avaition.Its approx equiv to 100 "pump" gas, but has a lean rating of 100 and a rich rating of 130.
MNZ Appendix E defines avgas as max 112 MON amd max 108 RON.

Avgas, or any leaded "race" fuel reacts completely differently to unleaded pump gas.
In general terms the unleaded hates compression, but loves timing.Avgas is the opposite in that it makes more power up to the knock limit with more com.
Unleaded makes better power when run rich,avgas makes more the leaner you go.
Tuning in the old days with RS and TZ engines meant using lean mains and small powerjets ( 35 ) as turning off a big jet over the top would mean being too lean in the overev.
Nowdays the unleaded fuel runs rich at peak power, then uses a big powerjet ( 55) to create some heat in the pipe over the top.

Race gas bought in drums really is" low lead race gas", nothing wrong with it - but hard to get the same stuff in many places.
The stuff in tanks at stations/tracks is "old" avgas.The best, and only way to be sure of what you are getting is to go to any local airport and buy Avgas - it is tested regularly and is guaranteed to be fresh and to spec - has to be, or the Lycomings would all fall out of the air - bad.

One thing I completely disagree with in the piston seizure write up is that air leaks cause a lean condition.
This is utter bollocks, any engine with a case leak will run richer, the bigger the leak the richer it will run.
Caused by the fact that the case "pump" no longer works and the fuel air mixture isnt being transferred thru the ducts.
If the engine is then leaned up to "fix" the incorrect mixture - then it seizes.

A leak between the carb and the reed or any intake will always add air going into the engine and create a lean condition.
A leak anywhere in the case, be it a gasket, a seal, or a pin hole in a casting will cause the engine to run rich.
Problem is that they then seize for no apparent reason when the jetting is then "fixed".
So its always wise to make a set of blanking plates and or use a rubber bung with a bolt that expands it into the pipe manifold, so that a leak down test can ensure no case problems exist.

Everyone uses the chamfered pin with plain clip now - but for years we had to cut the inner leg off TZ clips and add the chamfer to prevent the clips from popping out.
Dont know if Irving was the instigator of the idea, but it works a treat.
The angular contact bearings I dont think are a good idea for mains - as any side float will translate into vertical slop as well, so they must be run with preload.
Sort of the reverse of floating the crank - and thats worth easily replicated free Hp.

Primary com of 1.37 would be about right for the average transfer duct and port geometry being run.
If the descending piston compresses the volume, then its part of the case compression if its connected when the piston port is closed.
That plug looks way too hot for the application as well.

Well its a bit of a stretch to try and be specific with so many variables involved but I will try.
What you are dealing with is a combination of static com and the dynamic com created by the efficiency of the engine spec, along with the added quirk of small bores being able to withstand more of both.
The more an engines overall spec is synergistic and SOTA then the less static com is needed nor is it in fact desirable.
So - with very average port/duct geometry, a very average pipe design, a very average ignition curve but using Avgas, then at the very least we need 15:1 full stroke com to get close to optimum, with EX durations between 196 and 202, where you need to be to make any power at all.
Avgas burns so close to 105 unleaded race gas, in power and reaction to com that its indistinguishable on a dyno, except that Avgas will always withstand more com or a lean condition better. Unleaded hates com but loves timing - as a general rule, the opposite of proper race gas or Avgas.
As Avgas is allowed, and we are discussing small bore race engines with sub optimal ports/pipes etc then I would say around 15.8 would work fine.
On pump gas, be it 91/95 or crap 98 then reduce this to 13.8 and wind in lots of static advance.
Avgas isnt created for what we are doing, but its cheap enough,available at any airport,and works real well when pushed to the edge of the tuning envelope.
The other issue is that to be effective, the squish clearance should be just above what would give zero clearance in an overev situation.
Thus any 50 or 100 cc bucket is able to run down at 0.6mm with complete safety, without running into issues of excessive squish velocity, unless you are well over 50% SAR.
But dont give me any grief when the thing melts using an 8 plug when any engine making any power at all, should have a 10 iridium as a baseline.

Very interesting and Yes I would think it fair to measure 2-stroke CC's that way ........



It appears "compression cannot commence, before exhaust port is closed" untill you think about the role of the expansion chamber.



When you think about the plugging effect of the return pressure wave from the expansion chamber stopping fresh charge from spilling out of the cylinder as the piston starts on its way back up to close the exhaust port and maybe even stuffing some back in, in the last moments of closing.

You can see how compression of the fresh charge can happen earler than the exahust port closing point, effectivly making it a bigger engine when its "on the pipe". Some call it the supercharging effect..... whether it results in more than 100% volumetric efficency of the total swept volume I don't know, but it certainly gives more than a 100% of the swept area above the exhaust port.

There it is, the whole mistery of racing 2-strokes reveled in the last two posts, everything else is just detail, thanks Dutchee.

I think the analysis of the 2T working cycle when compared to the 4T in the example is a bit simplistic and missleading.
A full house 4T like say the Britten V1000 has a VE around 125% and an Ex duration of over 300*.
The 4T uses the exhaust tuning to create a depression during TDC overlap, giving the intake stream a chance to purge residuals out of the chamber.
In a 2T the Ex creates a depression around BDC, giving a Delivery Ratio of 1.25 ( same number effectively as the 4T ) and this purges residuals in the same way as the 4T.
BUT, the 2T uses the open Ex port in concert with the pipe design, to reverse the outflow,shoving clean, overscavenged clean Air/Fuel back into the cylinder, using a duration number closer to 200*.
The real kicker for the 2T is the huge efficiency gained by firing every revolution, doubling the Ex frequency, and thus the energy that can be used to good effect.

It may be semantics but why "change" the calculation of bmep for a 2T by doubling
it because it fires every revolution.
The bmep of a full house 2T is around 200 psi, as this is a calculated relationship between measured torque and displacement.
The calculation is a measure of the ability to produce power PER CYCLE, divided by the number of power cycles.
Thus a 4T has a higher bmep capability, but is hamstrung by the halved number of available cycles.
This is an inherent advantage of a 2T, you cant just factor it away in the calculation.
And the VE numbers are simply a measure of the amount of air ingested per cycle divided by the displacement, and are essentially the same for full noise designs.

Its a bit like the people that go on about the measurement of power on a dyno.
The guys with huge Harley engines say that the power should be "corrected" for the big heavy pieces of shit when compared to a small screamer 125cc GP bike.
The reality is that the big , heavy pieces of shit are exactly that, and what is measured at the rear wheel, is the actual power delivered in the real world.The fact that they have huge flywheels that absorb "power" to spin up, is an inherent
part of the design, and in my opinion cant be ignored by applying some fudge factor that makes them feel better, about the Hp/cc figures.

Page 340

[TZ350]

This is a collection of crank hp simulated graphs (93% combustion efficiency so overstated) of my current RS125 pipe and big port 30 rwhp, estimated 34-35 crank hp motor.

In the simulation the pipe peaks at 12,250 just like it does on the dyno and the simulated torque does not drop off all that much as the pipes header is shortened.

The simulations indicate a 6k power spread is possible but would you really want to rev an old 1978 Suzuki GP125 engine to 15K.

Its the high powered 6k power spread that I want (and yes Wob I know it won't be 40hp).

The simulations have got me interested in the Trombone pipe. I need my new pipe to initially peak lower and finish earlier than 15k.

So I am going to use EngMod2T to try and find out what I might be able to achieve.

[wobbly]

Having the torque peak at a low rpm ,then spreading the power out over a wide band is possible.
But very tricky to make work in practice.
Means several elements are effectively in anti phase, especially where they should work together and create lots of power.
But if you want broad power spread ,this will always limits the peak capability.
The RZ400 could easily do 100 RWHp, but then it wouldnt spin up off turns to anihalate SV650s.
And this is a road bike shitter with 102mm bore centres, that limits you in getting anything remotely like good duct geometry.
This result needs all manner of trickery, and solenoids,ATAC etc etc all are capable of extending things way better than simply good porting and pipes could ever do.

[TZ350]

Developing a virtial pipe using EngMod2T, and then make and test it in real life. I expect it will take a while and no doubt I will flounder around a bit but I am keen to give it a go . The occasional pointer when I am getting lost or off track would be appreciated.