ESE's works engine tuner

[F5 Dave]

Wow, every days a school day.

I've been making big radius ex ports purely for ring life, something a chap Ram told me over a beer in the 80s was to make the port top square & create an eyebrow top & sides so the piston sees fast opening flat but the ring sees a nice rounded port. Never to that level I don't think & it appears the assumptions were wrong, but I wasn't expecting that.


Ohh lookie, page 600.

[F5 Dave]

Y. . . .
By the way I built a racing lawnmower when I was 12 - does that count.

Depends, did you get paid per lawn, or by the hour?

[TZ350]

Page 600 ... there are other interesting link collections on most other decade pages. Or you can use Thread Tools and View Images to flick through the images and find associated posts.

On Page 500, Bucket has links to how Team ESE built their 26, 28 and 31 hp engines.

Page 500 .....
No need to have a peaky engine. Here are Two Very useful Tools. EngMod2T a 2-Stroke simulation package and a handy (and cheep) Porting Calculator from:- http://www.porting-programs.com/ which is based on Blairs work.

Gordon Jennings book Two Stroke Tuners Handbook.

http://edj.net/2stroke/jennings/
http://3cyl.com/mraxl/manuals/jennings/chambers.pdf

Back in the day, Jennings was the Bible and it is still a good read. He did a good job of unravelling the mysteries of port timing, but he did not give much emphasis to blowdown time area. This oversite of such an important aspect of 2-Stroke tuning is probably why its been overlooked by so many tuners and it probably held back home tuned strokers for years.

We know better now and the clever trick is to keep the Transfers low and wide to enable adequate blowdown without having to go to extremes with the exhaust port.

Bell was next.

http://www.2shared.com/document/2G7B...troke_Per.html

Then there was Blairs work and he put numbers to the exhaust blow down time areas required.

http://www.dragonfly75.com/motorbike/2StrokeDesign.pdf
http://www.prme.nl/download/engine-0.pdf
http://www.4shared.net/download/8hfj...n-P-Blair.html


STA Specific Time Area is port time area at a chosen RPM. STA underpins all 2-stroke design work.

This software is so good and so cheap you should get yourself a copy ......

Two-Stroke Porting Software.



Plan your ports with this software using Jennings and Blairs principles.

Porting Calculator and Port Analyser. $16.25 USD each. Paypal accepted.

These are based on Blairs and Jennings Books, makes it easy to apply their work to your motor. The program screen can be switched between Blair or Jennings and back again as you work.

Look at them here:- http://www.porting-programs.com/

I purchased mine over the net 8 months ago using Paypal and it was available for downland within hours.

Then when I claimed my free upgrade it to was quickly available.

Do go and have a look at his site:- http://www.porting-programs.com/.

Frits talks about 190 deg Exhaust port duration being the optumim and why......

Do I understand this correctly, given sufficient blow down and exhaust STA an exhaust duration of 180 deg would be the optimum at any rpm?

The short answer is yes.

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.

Is that where you explained that and why the ideal exhaust port timing is about 190 degrees?

Exhaust Port Radius.

I was recently re-reading the entire pit-lane thread on the RSA125 an noticed a brief mention by Jan Thiel of the radius that the Aprilia cylinder has at the exhaust port roof to improve flow... there are also two different duration’s mentioned for the RSA exhaust, one is 202* the other states "196* without taking the radius into account", or something to that effect...

Interesting stuff. Perhaps Frits might expand on this.

"As regards the exhaust port, a secondary function is served by providing a bevel,
and radiused edges, around the port window. There is a very considerably contraction of
flow through any sharp-edged orifice, and such orifices may be made effectively larger
by providing them with a rounded entry. Improvements in flow in the order of 30-
percent could be had were it possible to give the port window edges a radius of, say, ¼
inch. Unfortunately, to do this would mean advancing the point of exhaust-opening a like
amount, which in most engines would result in a very radical exhaust timing indeed. It
is, on the other hand, often possible to carve just such a radius at the sides of an exhaust
port - although it is questionable that this radius would be as effective as simply widening
the port to the same extent. The radius approach does have the advantage of leaving
intact much of the metal around the port, which can be important: Thick sections of metal
tend to equalize cylinder temperatures and prevent the kind of local distortion that is such
a potent cause of piston seizure."

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.

Since I am spilling the beans here: the top radius was 3.5 mm; it was tangential to the exhaust duct roof. That raised the timing from 196° to 202° when the first glimpse of light became visible.

I have just completed a back to back test on the Ex port radius in a TM 125 kart engine.
The cylinder from the factory was a special "tuned "expensive part number, and I was given a stock one to modify.
For sure the two were very different, the stock one being alot lower timing.
This was fortuitous,in that it enabled alot of room to be used to move ports.

First test was the stock cylinder with the main EX at 194, I put a big radius on the roof giving effective timing at 196.5 ( the trick cylinder was the same at 196.5 )
This instantly picked up power everywhere from 8000 to 14000, with alot better overev power, being 6Hp up at 14000
The next test involved dropping the cylinder,removing the chrome and regrinding the ports to the reverse stagger layout.
The A port being the lowest, to allow alot bigger Aux ports.
The main Ex port now opened around 192,with effective at 195 but the Aux opened at the same time, giving better blowdown area, as well as the flow enhancing radius on all 3 ports.

With the reverse stagger giving better transfer area ( as the B,C ports being high with alot of width compared to the previously high A port ) the engine now made 2 Hp or more than the factory trick cylinder
but was now 8 Hp up at 14000 and gained 400 rpm of usable overev, as previously it dropped dead at 13800 on track.
This setup proved to be quite insensitive to jetting and timing changes, allowing alot more static advance giving much better off corner power without killing revs as this would normally do.
Thus the enhanced blowdown flow of the radius at low port openings,allowed those much lower timings to be used effectively, enhancing power everywhere, but most importantly in the overev,where blowdown is most needed.

Frits is right when he says that the Italian factories are 3 years behind,as they still havnt started to use much of the technology developed at Aprilia even now.

There is more on Exhaust Port Radius below.




And Yamahas Ideas about what is important with transfers.

[TZ350]

Page 600 B

It seems that at high rpm and part throttle the pressure in the cylinder is higher than in the crankcase when the transfers open and hot burnt combustion gases back flow down the transfers.

Part throttle detonation is the current big issue for our 30+hp aircooled engine. Retarding the ignition on part throttle is only part of the solution.

More blowdown time area is required to lower the in cylinder pressure so opening the power valve further when closing the throttle at high rpm could be a solution.

Or the pressure inside the expansion chamber (and cylinder) could be lowered by having a second stinger pipe with a butterfly. Which is opened in high rpm part, throttle situations to drop the expansion chamber and cylinders working pressure.

And Frits proposes an idea where the intensity of the reflected wave is reduced by changing the size of the bleed venture at the end of the reflective cone.

Kel sent me this ......

jan thiel on part throttle deto

"I am 100% convinced our engine could have run for 6 hours at max power without seizing.
The problems arise when you close the throttle, or run part throttle!
The piston is mainly cooled by the transfer flow.
And at part throttle there is less transfer flow, causing detonation (auto ignition)
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.
At 100% throttle the engine was undestructible!
By making the transfer ports as wide as possible we had very good piston cooling."

No answer here but at least we are not alone with engines that fail on part throttle

I scraped the full coversation below from here:- http://www.pit-lane.biz/t3173p60-gp1...vermars-part-2

Brian Callahan
Jan or others, how did you control the tuned pipe wall temperature (or EGT directly?) when testing on dyno? This seemed the most difficult thing to mimic when testing either the GP engines at QUB or my R/C boat engines, in the lab. The inertial dyno or computer controlled brake seem to work best because we can match the test engine's acceleration with reality. On steady-state testing, EGT would simply climb 500, 600, 700, 750 °C until way past reality and the piston would seize.

Frits Overmars
This has always been one of Jan's greatest handicaps. He has asked for an inertial test bench over and over, but Aprilias race director Witteveen, or The Great Leader as we call him, never deemed it necessary....

Jan Thiel
When EGT goes up and up there should be some serious problem with the engine.
We never had pistons seize during our steady state tests.
Working on the dyno continuously 5 days a week!
I am 100% convinced our engine could have run for 6 hours at max power without seizing.
The problems arise when you close the throttle, or run part throttle!
The piston is mainly cooled by the transfer flow.
And at part throttle there is less transfer flow, causing detonation (auto ignition)
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.
At 100% throttle the engine was undestructible!
By making the transfer ports as wide as possible we had very good piston cooling.

As Frits has written, I would have liked to have also a dynamic testing possibility, with a flywheel.
In my opinion you should simulate a straight, starting at around 10.000 rpm, and shift through the gears
until you reach top speed. And with the airbox as used on the bike, with a ventilator that simulates the raising
air speed as it would be on track! Maybe it is interesting to know that without a ventilator the engine gave
less power with the airbox fitted.

I was told that such a testing system was too expensive.
And unnecessary as we won anyway!

I can also see a disadvantage of 'dynamic' testing.
Because the duration of the test is so short you can get away with very extreme (too extreme?) settings,
without damage.

GrahamB
Remember that retarding the ignition is used at high rpm to increase exhaust temps and effectively shorten the pipe. So it's likely to increase the heating of the front edge of the piston...

Haufen
Yes I know, but part load egt is usually lower than full load egt. And I think most of us would prefer higher part load egt over part load detonation. Of course, how far one could go and how far one would need to go would have to be tested, and how much would be needed would depend on the engine.

Mic
How about much larger travel on the exhaust power valve.
With a shorter exhaust port duration power is lower. And this is already controlled with the stepmotor over the ECU.

Jan Thiel
This causes detonation (auto ignition)
The problem is that the burned gases do not exit the cilinder!
Retarding ignition also does not make sense.
As you have an AUTO-inition problem!
So the engine does not 'listen' to its ECU anymore!
What you would need is the same fresh gas flow, but with less HP!
Not easy to achieve!
A variable tailpipe might help.

Jan Thiel
Haufen, We also had such a test bench at Aprlia.
The prototype of this test bench was developed by Apicom in collaboration wit Aprilia.
So we had it first, and now anyone can buy it.
It was helpful but not what I wanted.
A so-called step test.
And without the airbox!

Frits Overmars
Like Jan wrote, a shorter exhaust duration will worsen the detonation. What happens is this:
During normal operation, the blowdown time.area of the exhaust ports is sufficient to drop the cylinder pressure below the crankcase pressure before the transfer ports open, even at high rpm.
At part-throttle that cylinder pressure will drop to the same level, but now the crankcase pressure is much lower and exhaust gases will enter the transfer ducts, contaminating and heating the fresh mixture even before it enters the cylinder.
A theoretical solution would be a power valve that enlarges the normal exhaust timing instead of lowering it. But that is impractical as it would ruin the shape of the exhaust duct and it would cause cooling problems in the cylinder's exhaust area.
A variable tailpipe area, like Jan says, can be a more practical approach. I designed a simple solution, shown in the drawing below, but then two-stroke development at Aprilia was terminated because of Dorna's ban on two-strokes

Howard Gifford
Another way to lower HP without sacrificing piston cooling would be to richen the mixture when you want to lower the power. With a signal to a fuel enrichening solenoid you could achieve a power range. It would then be instantaneous and programmable. Not enviornmentally friendly but would work for racing. The mixture ratio difference from high power to low power would need to be just rich enough before a misfire and just lean enough for sustained high power.

The variable tailpipe idea will work but I suspect the pipe temperature would drop off and it would take several seconds to regain full power. But then again rich mixture may have the same problem.
Two strokes are like redheads. Hard to figure out and very temperamental. But when they are happy they are a lot of fun!
HG

Jan Thiel a écrit:
The entering fresh charge is ignited by the remaining, hot, burned gases!
You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? I did not find a solution before I retired.
And nobody else was really interested.

Institute of TwoStrokes
On aftermarket ignitions I use there is a mode I can switch on where a number of indivdual sparks are cut, depending on throttle position. It is now only configured for cutting 1 in every 3 sparks on over run(tps <10% with high rpm). Would that sort of system solve the part throttle detonation? If the number of sparks cut could be varied along with TPS for this to begin and end? If it would be helpful I'm certain the manufacturer would only need a software change to do this.

Jan Thiel
I certainly thought about cutting sparks.
But remember: the problem was AUTO-ignition!

GrahamB a écrit:
Remember that retarding the ignition is used at high rpm to increase exhaust temps and effectively shorten the pipe. So it's likely to increase the heating of the front edge of the piston...

Jan Thiel
Indeed, retarding too much caused detonation!

Institute of TwoStrokes a écrit:
Jan Thiel a écrit: The entering fresh charge is ignited by the remaining, hot, burned gases! You can see very severe damage to the piston after maybe 10 seconds at 20% throttle.
This still is an unresolved problem! I was thinking about a way to reduce engine power without closing the throttle. But how can you do this? On aftermarket ignitions I use there is a mode I can switch on where a number of individual sparks are cut, depending on throttle position. Would that sort of system solve the part throttle detonation?

Frits Overmars
As Jan pointed out, once you have auto-ignition, the engine does not listen to its ECU any more. So you would have to start skipping sparks well before the onset of detonation.
In a foul-stroke your proposed system does work, but a two-stroke would react far from linear. For example, if you skip 1 in 4 sparks, you will loose much more than 25% of engine power because that one missing spark will cause the gasdynamics processes to collapse. The main problem would be to realise a smooth transition from intermittent to full ignition.


Jan Thiel a écrit:
Retarding ignition also does not make sense.
As you have an AUTO-inition problem!
So the engine does not 'listen' to its ECU anymore!
What you would need is the same fresh gas flow, but with less HP!
Not easy to achieve!
A variable tailpipe might help.

Haufen
I think I expressed myself unclearly. What I meant was the following:
Imagine your engine with the throttle opened just above the auto-ignition range. Then you have sufficient transfer flow, but too much power. To lower the power, now retard the ignition. Then you still have sufficient transfer flow, but with less power.

I think Honda used auto-ignition to their advantage on two-strokes. As far as I remember they did it with a (very) variable exhaust power valve.

Frits Overmars a écrit:

Mic a écrit:
How about much larger travel on the exhaust power valve. With a shorter exhaust port duration power is lower. And this is already controlled with the stepmotor over the ECU.

Frits Overmars a écrit:
Like Jan wrote, a shorter exhaust duration will worsen the detonation. What happens is this:
During normal operation, the blowdown time.area of the exhaust ports is sufficient to drop the cylinder pressure below the crankcase pressure before the transfer ports open, even at high rpm.
At part-throttle that cylinder pressure will drop to the same level, but now the crankcase pressure is much lower and exhaust gases will enter the transfer ducts, contaminating and heating the fresh mixture even before it enters the cylinder.
A theoretical solution would be a power valve that enlarges the normal exhaust timing instead of lowering it. But that is impractical as it would ruin the shape of the exhaust duct and it would cause cooling problems in the cylinder's exhaust area.
A variable tailpipe area, like Jan says, can be a more practical approach. I designed a simple solution, shown in the drawing below.

Attachment 269228

Haufen
I think I have not gotten behind the variable tailpipe idea, yet. What would you like to vary with it and to achieve which effects? At little throttle openings the pressure inside the exhaust pipe is already very close to atmospheric pressure (if not even) on most engines. And if you had say 100mbar inside the pipe at the critical throttle opening, then the engine might have had more power with a bigger tailpipe.

Attachment 269228

Frits Overmars
'Opening' the end of the reflector will cause a substantial weakening of the reflected pulse and thus less charging of the cylinder. Izze simple, no?

Haufen a écrit:
Variable transfer timing would be nice also, if feasible.

Frits Overmars
That would be my ideal. Lowering all the transfer roofs would shorten the transfer timing and lengthen the blowdown timing, so the cylinder pressure would drop further before the transfers would open. It would cure the hig revs/low power-detonation and it would improve the power band because a too early-returning exhaust pulse would have less opportunity to push the fresh cylinder contents back into the crankcase.
A controllable transfer height would even make a throttle valve unnecessary.
There's only the little problem of how to build it...

Jan Thiel
Haufen, Auto-ignition usually occurs between 10 to 40% throttle at high revs.
In fast, non full throttle corners.

Retarding the ignition was tried to diminish power.
This makes the exhaust very hot.
Then, when you need full power, it is not there because the exhaust temperatures are wrong.
This takes a little time, when the engine is back to full power you are already at the end of the straight!
The same goes for water injection in the exhaust.
It was tried by Rotax about 25 years ago.
There was a LOT more power at low revs, so the rider had to take it easy when opening the throttle.
But the engine revved a little bit less, because the exhaust temperature did not recover at high revs.
And lap times became actually slower.
After a day of testing the system was switched off.
Lap times immediately improved!

A very important thing when accelerating is the power you have after changing gear.
Spark interruption may be not so good for this!
As I did not have the dyno I wanted this gearchange effect could not be tried on the dyno, very regrettably!
Retarding the ignition and weakening the mixture by powerjet can also have a negative effect on this.
The exhaust temperature should be 'Right' for the No. of revs after you change gear.
If the temperature is too high there will be less power!
So it is REALLY complicated!

[TZ350]

Page 600 C

Knock Gauge

I have just been putting on my knock gauge on the bucket and when I run her in the drive with the sensitivity set half way, reving the bucket up the gauge went off like a christmas tree and I am wondering what others have there gauges set to?
The gauge is from http://www.knockgauge.eu and the sensor is off a subaru car. It's mounted on a 100cc LC two stroke on a head stud straight onto the head with nothing inbetween if that is any help.

I could even get the deto light showing revving it in neutral - & that was after finding the point of best power was somewhat advanced of where I started & progressively increased till I went too far & went back a little. Wonder if an aircooled motor 'rings' so much that it is not useable?

Been away winning races so will reply now re the deto box.
Calibration is easy, turn it down real low such that the green lights do come on when doing a full throttle run.
Keep turning it up till you get a deto indication somewhere in the powerband, going up on full throttle, or as TeeZee found, when backed off on the overun.
In short - believe what you are seeing, if it shows deto on the overun, then, its got deto in the overun.
This MAY not be an issue when racing as you MAY not damage anything detoing for a short period under these conditions.

But,of course if you have a TPS this means you can use a 3D map, and its easy to pull out a couple of degrees of timing at that point, and the deto will go away - simple.
I found that maximum performance on the dyno meant you had short flickers of deto at nearly all rpm on full throttle,and it lights up when you hit the limiter.

I do several pulls at 1/4, 1/2 and 3/4 throttle,running up against the dyno load, as well as running down on the overun. to generate the TPS driven curve shape.
This enables you to dial up the max advance needed everywhere, then go into the software and back the whole curve down 1 to 2 degrees.

Now you have a good curve shape that the engine actually needs, and any issues on track, can then be taken care of by the box switching the retard input to pull out 2* to prevent unforeseen meltdowns.
I havnt used the deto setup on an aircooled, but I suspect that the deto ringing frequency signal is much bigger amplitude than a watercooled cylinder,meaning you get a much quicker indication of deto approaching.

Means its very sensitive to adjustment, but I say again, if it is flashing deto at one rpm and not at another, then believe what you are seeing, just turning it down so it does nothing, is dumb.

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.

The piezo sensor will easily show the missfire from hitting the limiter, so it will also show a big end knock, as well as the piston hitting the head.
Dont know about excessive piston slap , but probably.
Plenty of "noise" sources in a 2T.

The Knock Gauge can easily be adapted to be a Det Counter as well if you buy it with option 1 for retarding the IgniTec’s ignition and option 2 for a 0-5V pulse signal out for each det the a Counter can see.

Quite a bit of info on counters you could use with the Knock Gauge here:-

703TR002N-512D RS part number 183-5952 $63.50 ... 5-12V and less than 10mA so easily self powered and at 500Hz fast enough to count all deto events as seen by the Knock Gauge or similar, as 200Hz in a 2-Stroke equals 12,000 rpm.

Someone elses links list:-
http://www.rzrd500.com/phpBB2/viewtopic.php?t=2438
Might be worth a look.

This problem reminds me of an issue I had with my TS/RGV motor years ago. On the dyno at certain times you could see flames dancing round inside the carburetor. This was a full crankcase reed conversion. After a long time, over a year, in an attempt to fix the problem I just advanced the timing as far as it would go. The flames disappeared and it starting making modest power.

It seems from what people have been saying that this problem of detonation is evident on all(?) high performance 2-strokes. There may be a small number of cures but for whatever reason they have never been implemented. Thinking about it this could be what stopped my bike at Taupo. The piston was certainly hammered with cracks all over and Dave did say he was cruising in the corners which probably created the conditions needed for the problem to manifest.

The simplest answer seems to be to ride hard, maybe even changing down shift patterns - letting the revs drop as you brake and then dropping the gears as needed from lower revs.

More on Exhaust port Radius's

I have thought of it like so: The 3.5 number is the radius of the fillet applied.



In my pic at least, there are (exaggerated): the top corner radii ^ the top edge radius until 196* ^ the drawn red radius until 202*.

I think the flat sound to the exhaust is due to the top exhaust port chamfer blunting the exhaust note as the port is no longer cracking open suddenly.

If you only added a chamfer to the existing port, outflow will improve, wasting less energy in turbulence and sending more energy the pipe. It will also have raised the exhaust timing, opening the port when cylinder pressure is higher; another reason for the pipe to perform better.

I believe the big radius at the bore centre line has two effects.
Firstly is to improve the bulk blowdown flow at low opening angles of the piston controlled port orifice, due to the gas attaching early to the roof.

Secondly the exiting wave amplitude is lowered and smoothed out by the gradual ( instead of a sharp edge ) port opening.

This would improve the scavenging action bandwidth, but the peak value is probably then raised as well, simply because the port opens earlier when the pressure above the piston is greater.
Thus you get the best of both, a wider effective scavenging action, combined with a higher peak value, making the pipe work better over a wider range.

The 75% area at the cylinder exit is just something I discovered after running hundreds of sims, most of them worked best with an oval to round transition in the flange that started with this area and the pipe header diameter equalled the total effective area of the ports.

Its been tested and proven so many times now, by so many other people, that it should be the first mod to make to any T or triple port engine.

Here is a pic of one I have just done, that happened to have a tapered spigot - enabling the Aux ducts to be run all the way down into the pipe.



Check the big rad on the transfer duct/bore edge.

In all the engines I have done the area at the flange face is approx equal to the main port effective area, or approx .75 of all 3 ports.
The header diameter is equal to the effective total of all three ports.

The trend has been for a long time to reduce the volume of all the ducts in modern engines.

Aprilias Ex duct had the bottom filled in such that it was higher than BDC and the corners filled to reduce short circuiting from the A ports.
And the cylinder duct vol was CNC machined to be smaller and smaller in total vol, but in the process heavily promoting flow from the Aux ports to increase effective blowdown flow.

One of the transfer duct entrys was smaller than the port area ( the B and biggest port ) and for sure the ratio between the A and B port duct entry areas was tested
to death within the limitation of the case available area between the studs, by several of the 100 R&D festerers.

The idea here is to reduce the inertia of the initial volume available to the cylinder, that has to be accelerated out of the duct by the negative pressure ratio across the port.
That Cagiva cylinder is very "old" technology.

The secondarys facing each other relatively flat will always collide, but the hooks rotate the flow under the boost as it exits the port ( easy to see with the tap water Jante trick),clearing out a big "dead" area
in front of the rear port.

All modern race engines have a nozzle restriction at the flange face, as big T ports and tripple Exhausts loose alot of velocity going into the header.
Rule of thumb is a 75% of the effective EX area at the flange.
Stepped oval duct into a round flange does work, but I have used a CNC oval to round transition in the spigot for years, as has Honda in A kit, and Aprilia factory engines, this works way better.

The stinger nozzle effectively removes the stinger tube length from the equation - it was developed for Spencers NSR that had one stinger 150 long, the other was 450. The nozzle is around 2 to 3mm smaller than the tube stinger .

Simple answer re the odd shape and reduced area of the Ex duct exit is that with a 3 port cylinder, the area of the main port is plenty big enough to support the gas flow
created by the power being made.

The big Aux additional area allows better Blowdown STA, but this area is only needed above TRO.
Thus having a huge duct simply drops the velocity, reducing the wave amplitude into the header.
The Aprilia shape promotes the flow from the Aux ports by keeping the extra horizontal area all the way into the pipe - thus helping blowdown flow and overev power..

Reducing the duct vol by having area reducing steps, keeps the velocity high and again promotes the flow regime in the side ports. There may be a case to say that the steps reduce backflow from the pipe at low rpm when it is too short,but for sure there is no outflow disruption,and in any case tests showed that power went up as the duct became smaller.
I have exhaustively ( pun ) tested the vol/shape effects on a T port ( as has Mr H ) and an oval to round transition with no steps works better. A factory A Kit has a very small 41 by 32 oval, with a CNC transition into a 41 header.

Tuning using the exhaust gas temp.....

One thing you wont get is deto of the end gases without loosing power.
The phenomenon of deto is caused by temp/pressure creating free radicals, this process eliminates a huge amount of the available energy in the combustion fuel.
And once the radicals are formed, they are self-sustaining, and cause a runaway reaction process - consuming more energy.
This is exactly why the egt drops when you are too lean, and deto starts - no energy left to create heat - ie no power.

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 equivalent 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.

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 wouldn’t be the fastest by a mile as we were.

[Haufen]

When making that kind of bevels at the exhaust port on plated cylinders, how do you keep the ring from catching aluminum and smearing it onto the cylinder bore?

[twotempi]

Yea right ok guys, lets quit dick measurements, and get on with posts that help others understand 2T workings.
By the way I built a racing lawnmower when I was 12 - does that count.

Just for interest I read the the Bonneville speed record for a lawn mower was 84 mph !! It is currently held by a English guy from the land where they race these . A good example of what can be done, as opposed to what should be done ??

[F5 Dave]

Right that does it. there's enough other threads in the bucket section with people telling us how our sport should be, I'm going to find a lawnmower racing forum & give them brain damage about how they should be racing on standardised Classic Rye with a cut height of 9mm.

[Frits Overmars]

Frits, for the purpose of implementing and testing this radius is there a ratio to apply based on area, timing, etc? Is 6deg effective timing the magic number to work towards in say 2 deg steps? In the attached drawing AP125-01 does the broken line above the exhaust port represent the area the radius is applied to?Attachment 269598 Attachment 269597

To keep things surveyable you might say the radius should be a function of the engine's stroke.
Those 6° is not a magic number. In fact it doesn't even exist: the difference between 196° and 202° is only 3° either way .
Working in 2° steps is not likely to get you to an optimum. In the development of the Aprilia cylinders all cylinder dimensions were varied in 0.25 mm steps.
Just think of the number of possible combinations! It was one of the jobs that kept a racing department with over a hundred people busy for over 12 years.
The dotted lines above and below the exhaust port in the drawing do not indicate a radius but a chamfer. The radius came later.

Since I am spilling the beans here: the top radius was 3.5 mm; it was tangential to the exhaust duct roof, but not quite tangential to the cylinder bore; that would have been extremely difficult to produce. Instead the centre of the radius was offset a little to the inside of the bore. That raised the timing from 196° to 202° when the first glimpse of light became visible.

[Frits Overmars]

When making that kind of bevels at the exhaust port on plated cylinders, how do you keep the ring from catching aluminum and smearing it onto the cylinder bore?

You don't. First you make the bevels, chamfers, radiussses or whatever. Then you have them plated.

[wobbly]

Doing the lawns meant I was allowed to stay up and watch Maxwell Smart.
Grinding the Briggs cams with an angle grinder ,taking out the thick head gasket and using copper sheet, and drilling the jets for Alcohol meant i did the job in less than 1/2 the time.
Been doing the same shit ever since.

As I alluded to in my post about the KZ10 testing, I had to get the chrome removed from the bore so that I could do the big rads on the Ex ports.
Means after the Nicasil is plated you can polish the bore edge around the rad and blend into the alloy of the port roof, thus keeping the bulging ring on a hard surface at all times.

[husaberg]

http://shop.yoshimura-jp.com/en/prod...ai.php?id=1385

ON the topic of rather than relating to the pic
"Suzuki engineers discovered slots in Intake trumpets in the airbox would dampen out intake pressure waves,resulting in smoother torque and throttle response at midrange and and higher revs? GSXR1000"

PS MR Wob you have an outstanding PM from me in your inbox ..nudge

[Drew]

You don't. First you make the bevels, chamfers, radiussses or whatever. Then you have them plated.

Thank fuck someone actually pointed out that 'radius' is the wrong bloody word. I'm a dumb builder, but we would say chamfered or more likely beveled.

[Sketchy_Racer]

Thank fuck someone actually pointed out that 'radius' is the wrong bloody word. I'm a dumb builder, but we would say chamfered or more likely beveled.

Well, the shape is measured by is radius (or radii if it's plural ) but according to construction geometry the shape would be most accurately defined as a fillet.

A chamfer is a angled flat between two surfaces, as is a bevel.

[Ocean1]

Well, the shape is measured by is radius (or radii if it's plural ) but according to construction geometry the shape would be most accurately defined as a fillet.

Is current terminology in most CAD app's, eh?

I was taught that fillets were internal, though.