ESE's works engine tuner

[diesel pig]

Diesel - here is what you want in a nutshell.
The transfers dont need any chamfer at all as the ring does not bulge outward into the relatively small chordal widths.
All they need is the edge at the bore broken with a cotton mop.
A proper " chamfer " at a transfer timing edge creates severe flow eddies off the corner , causing the transfer stream to loose coherency and thus directional control.

The big radius on the Aprilia Exhaust timing edge was instituted by Jan in response to his boss producing a new exhaust design that lost alot of top end.
Increasing the Blowdown efficiency by dramatically increasing the just opening ports Cd value , proved to eventually give more power everywhere.
Many years later I discovered that if you do an STA analysis on the ports , it would appear that the transfers were some 10% ahead of the Blowdown capability - just from the raw chordal data.
But the clever implementing of an increase in Cd of the Exhaust port ( that the sim code cannot recognize unless its written in as an option ) would in reality , bring the two most important sets of port data back into alignment.

Great stuff! So with what you were saying about the Aprilia exhaust port history do I take it the exhaust edge radius only works to a power advantage with 10% undersized ports? Or does it work to a power advantage with properly sized exhaust ports?

[wobbly]

At the outer limits of power capability the Transfers and Exhaust Blowdown are fighting over the same real estate.
When I mentioned to Jan about the disparity between the STA numbers , his first reaction was that he should have tried lowering the Transfers.
He had said previously that they were never changed in timing , only area/direction.
Thus as always hindsight is all seeing, as his development concentrated on getting more Blowdown , firstly by enlarging the Aux , then increasing the main port Cd with a radius.

I have no clue if dropping the Transfers and keeping the original Exhaust port geometry would have worked , but if Aprilia R&D had an accurate sim package with inbuilt STA analysis , the disparity would have been obvious
immediately - maybe giving the insight needed into a previously unimagined development route.
Sadly the great leader told me in person that sims were an unnecessary waste of time , same thing I thought about him as it turned out.

[SwePatrick]

Next weekend is raceweekend, so we just wanted a little shakedown to see if everything worked.
No adjustments made for traction at all.

We reached 142km/h in roughly 100-110m (87mph in 330-345ft)
So i´m hoping for personal best upcoming weekend

[diesel pig]

At the outer limits of power capability the Transfers and Exhaust Blowdown are fighting over the same real estate.
When I mentioned to Jan about the disparity between the STA numbers , his first reaction was that he should have tried lowering the Transfers.
He had said previously that they were never changed in timing , only area/direction.
Thus as always hindsight is all seeing, as his development concentrated on getting more Blowdown , firstly by enlarging the Aux , then increasing the main port Cd with a radius.

I have no clue if dropping the Transfers and keeping the original Exhaust port geometry would have worked , but if Aprilia R&D had an accurate sim package with inbuilt STA analysis , the disparity would have been obvious
immediately - maybe giving the insight needed into a previously unimagined development route.
Sadly the great leader told me in person that sims were an unnecessary waste of time , same thing I thought about him as it turned out.

Is there a rough rule for the radius diameter vs exhaust port size? Or is it a matter of taking what was done to late model Aprilia cylinders and trying it out?
I must say things like this made the self important people who said two stroke development had reached a dead end in between the years 2000 and 2010 look like the pompous idiots they really are.

[Frits Overmars]

Is there a rough rule for the radius diameter vs exhaust port size? Or is it a matter of taking what was done to late model Aprilia cylinders and trying it out?

Here you go Diesel.

[diesel pig]

Here you go Diesel.

Perfect! With it in percentages it can be converted into any size. Top Man.

[OopsClunkThud]

Frits, I'm curious about the process of arriving at the radius of 5% of stroke.

Backing into the result...
In 2D CFD analysis the vena contracta is almost nonexistent when the port first opens and grows as the pressure ratio falls. A larger radius will have a more gradual port opening as the effective downward angle of the port swings from 75° to whatever the port roof is ~20-25° A Radius of 5% makes this transition in ~3.5° and seems optimized for a pressure ratio of ~1.6 or about the end of the blow down phase. This makes the radius large enough to prevent separation through all of blowdown, but would need the timing edge adjusted depending on where the radius is relative to the original timing edge.

If the timing edge were held constant with the radius effectively built up on the roof of the port, then the early blowdown phase will flow less because the radius blocks the path.
If the port roof were held constant with the radius being further cut upward then the timing is truly changed with blowdown starting earlier.
Using the wire bent at 45° to measure the timing edge seems to split the difference.

[wobbly]

I would be interested to see the CFD analysis where , as in the Aprilia the radius I believe started at 202* duration , but the actual port roof angled at 25* was 196* - and measured
with the 0.7mm gauge the effective timing was at 198*.
Would be interesting to know what the original conventional roof timing was.
But what happens a bit further down the duct is just as important in my recent testing. For best power the 25* down angle turns into a convex radius , and the port floor is horizontal to the point
where the side ports enter the main duct, and then turns into a downward angled ski jump.
This minimizes the main duct area , exactly where the side ports are increasing the effective total.
When combined with the 75% exit area , this configuration gives a huge increase in power everywhere, simply changing the duct geometry.

[SwePatrick]

Honestly, i don´t think it´s needed to follow the blueprint 100% on that radiused top of exhaust.
As i know that when putting velocitystacks on a inlet (fourstroke), is like the first 90% of gains is just a chamfer on the straight pipe.

[Frits Overmars]

Frits, I'm curious about the process of arriving at the radius of 5% of stroke.

Patrick, that 5% value was established empirically and given the number of possible combinations (the size of the radius and the offset of its center relative to the bore) we cannot exclude that the optimum might be a percent more or less.
I've always been playing with radii. It started when, at age 15, I radiused the piston top edge of my moped. Of course I didn't know what I was doing, but it worked.
I started fiddling with the exhaust port timing edge after reading about it in a book that I cherish. It is older than I am and it was written by professor Alfred Jante. He came up with 5%, also established empirically .

I would be interested to see the CFD analysis where , as in the Aprilia the radius I believe started at 202* duration , but the actual port roof angled at 25* was 196* - and measured with the 0.7mm gauge the effective timing was at 198*. Would be interesting to know what the original conventional roof timing was.

Both the 196° timing before radiusing the top edge and the 202° timing after radiusing were established with 'first light' visible at the ports top edge; no 45°-bent gage involved. I came up with the bent gage later, when trying to establish the effects of combined radii at both the port top edge and the piston top edge.

what happens a bit further down the duct is just as important in my recent testing. For best power the 25* down angle turns into a convex radius , and the port floor is horizontal to the point where the side ports enter the main duct, and then turns into a downward angled ski jump. This minimizes the main duct area , exactly where the side ports are increasing the effective total. When combined with the 75% exit area , this configuration gives a huge increase in power everywhere, simply changing the duct geometry.

Wob, I am well aware of the excellent results that can be achieved with your exhaust duct geometry. However I think that minimizing the main duct area, exactly where the side ports are increasing the effective total, is not a goal in itself but a consequence of the fact that the cross flow area upstream of this minimum area is larger than it ought to be.
Raising the exhaust floor to about 10 crankshaft degrees below Transfer Opening would reduce the initial port area while leaving sufficient blowdown angle.area for even the most enthusiastic overrev. It would also reduce the risk of transfer short-circuiting, it would influence the horizontal course of the port floor, reducing or eliminating the ski hump, and it would raise the exit area value to over 75%.

[OopsClunkThud]

Honestly, i don´t think it´s needed to follow the blueprint 100% on that radiused top of exhaust.
As i know that when putting velocitystacks on a inlet (fourstroke), is like the first 90% of gains is just a chamfer on the straight pipe.

But if you were going for that 100% an ellipse with a semi-minor axis of 5% and a semi-major axis of ~10% would be even better than a radius.

[wobbly]

Frits I have signed an NDA with another KZ engine manufacturer who is desperate ( and has all the resource ) to try all of the things we have been discussing.
Initially all my work will be remote , in CAD ,up until the end of August where I am committed here to winning our KZ National Title again.
After that a flying visit to you and Marc is pretty much a done deal.
First order of the day is to do the cylinder/pipe analysis in EngMod , then carry on where Jan left off with the floor at 3mm ABDC.
Maybe I can retire when its at 9mm above.

[Frits Overmars]

Frits I have signed an NDA with another KZ engine manufacturer who is desperate ( and has all the resource ) to try all of the things we have been discussing.
Initially all my work will be remote , in CAD ,up until the end of August where I am committed here to winning our KZ National Title again.
After that a flying visit to you and Marc is pretty much a done deal.
First order of the day is to do the cylinder/pipe analysis in EngMod , then carry on where Jan left off with the floor at 3mm ABDC.
Maybe I can retire when its at 9mm above.

I'm looking forward to it Wob

[Peter1962]

Confused i thought 1000km or so for the pistons half that for the rings with the cranks about 2000km that prior the big bangs. the price of power i would guess the 125 ad 250s were changing stuff at a much quicker rate.
pistons every race cranks at 100

Frits I have signed an NDA with another KZ engine manufacturer who is desperate ( and has all the resource ) to try all of the things we have been discussing.
Initially all my work will be remote , in CAD ,up until the end of August where I am committed here to winning our KZ National Title again.
After that a flying visit to you and Marc is pretty much a done deal.
First order of the day is to do the cylinder/pipe analysis in EngMod , then carry on where Jan left off with the floor at 3mm ABDC.
Maybe I can retire when its at 9mm above.

That is great news !
Will this assignment also give you the opportunity to experiment with longer conrods (like aprilia had in the RSA, in sharp contrast to the short honda conrods ) or is it limited to the current 110 or 115mm that is used in KZ ?

I am gonna be cheering for you, winning the KZ Kiwi national title !

[rgvbaz]

Last issue I saw they retested and got it to 95mph but it wouldn't pull 6th. They are getting a non-standard size sprocket machined to try and get the gearing right. The next issue should be out here soon!

Cheers

Dave

Well I'd been looking out for the latest issue to see how they are doing (mag takes months to get to NZ so we're out of date - yeah yeah)

Ran to 106mph on the dyno at 12,000 which I think was well past their peak power. Net result so far; 87mph but unable to hold 6th gear. They had jetted down a step to try improve (where they got 87) & it nipped up. Apparently was just getting too hot between runs & not jetting fault.

I'd argue that aircooled bike is petrol cooled & it has to run that bigger than optimum jet.

Either way they are cleaning it up & rechecking on the dyno so we have to wait another month (unless we get a spoiler from overseas guys). They will try gear it down if they can't pull 6th this time. Frankly I think it was crazy they didn't have a range of gearing for a top speed attempt on a Tiddler.

I still predict 92mph. I am not trying to knock them, it is a good effort & the bike looks great for what it is, true to the original idea rather than a liner attempt (they drafted a kid to ride it). I just think a bigger carb & some more revs would have helped their cause somewhat.



[edit] July issue, just looked on site & Aug issue advertised so we're not that far behind, but no mention of it in blurb.

Not sure if anyone would still be interested but I happened upon an AR 50 a few years ago and then an Autisa 93cc kit tuned by BDK racing plus pipe.

I'm going to have a go at cracking 100 mph with it.

I'm documenting it on YouTube at the min. https://youtube.com/playlist?list=PL...nQKVCOpZJtxZCl

Cheers,

Dave