ESE's works engine tuner

[Flettner]

Frits, why does the back port (boost port) always need to point upward at an angle. As you said the FOS cylinder has a stable gas flow (plume) even if one port is blocked off. With modern cylinders the transfers are starting to tuck right in under the exhaust, so the transfers could all be arranged as in your FOS cylinder with the rear port having much more effective area because it doesn't have to be at that upward angle?
I've changed one of my engines to have a rear port just like a side port, it went very well, perhaps I just thought it went better?

[F5 Dave]

Sorry all. But how do I rotate the pictures ?

I thought, Whoa, cool display. . . . oh hold on.



Lionel Richies Bikes? (sorry I hated that song).

[peewee]

wobbly just so i understand. is this how the exh spigot should look ? i made a 5mm spacer which i might or might not use depending what engmod says but if i use it then the aux tunells will have a smoother transition to the main port. this engine seems to have a rediculously short main exh tunell. likely because there wasnt much room at the front of the chassis im sure. also the cylinder is at the machine shop getting the bore straightend back out and the gasket surfaces machined flat. should have it back by friday i hope then bolt it on the crankcase and start engmod

[wobbly]

NO - the aux tunnels should be ground outward at the flange face, then smoothly transition into the round
exit of the spigot.
This pic is of a KZ2 kart cylinder, and the spigot is tapered on the OD, allowing the extended aux width.
The Aprilia is similar but as far as I know they never had a proper smooth transition within the spigot - all the
pics I have seen still had steps.

[Lightbulb]

Blended exhaust, this is what I made for our 6.5cc engine, the reduction at the oval is 75% of the projected exhaust area. I did not take into account curvature of the liner, radius 10.19mm. The shape to oval takes place over a distance of 7mm at the shortest part, about 10 mm at the corners for the top and outer edges of the exhaust. The pipe header is 15.0 mm diameter, and the oval is 15mm wide and 9.9 mm high. From the oval to the diameter, That part was turned as a taper from 15mm to 9.9 mm diameter. Then I just used a 3/8 endmill to make a slot through the assemble cutting an oval 9.9 x 15.
You can see from 1 picture the shape of the exhaust and the faceted looking blend, but that is the cad. Then you will see the round to the oval and the bottom area that has a small step.
I tried an adapter that was like a wire cut from the oval to the diameter 15mm header. But there was no measureable power gain or any benefit from the extra work compared to the turned taper and an oval slot put through.
The oval to round is over a length of about 20 mm or so. It's not a motor bike but the idea really does work. I can't tell you why exactly that it works though. Hopefully this will be of some help to someone.

[husaberg]

Ten ...................


I can't remember where the Aprilia race website info is?
Edit yes I can
http://www.serviceaprilia.com/public...GP&Contafile=1
In 1989 25 replicas 250's were sold
In 1992 Aprilia sold 40 RSV250's
Around the same time Honda Sold 150 RS250's and 500 RS125
If I take a guess then I would say no more than 125-135 or so 125's would have been made per year?

I wouldn't be surprised if sales went up a bit after 1995 when Jan Thiel joined Aprilia etc...

(These are customer bikes)

In 1988 aprilia made 30 250cc race bikes
In 1992 aprilia made 40 250cc race bikes manufactured
Thus I'm sure there after there were greater numbers of units made up until a point when racing numbers began to fall.
How many of each model is made now 2015

Jan Thiel Pitlane
The most time was spent narrowing the bridges in the exhaust duct.
These could not be CNC machined:the inside was unreachable.
Preparing for plating took about half a day.
And preparing for dyno testing another half day.
A cylinder 'untouched' after plating would give 1,0 to 1,5 Hp less.
All cylinders destined for 'works' riders were dyno tested.
And reworked in case of missing HP.
We could dyno at maximum 3-4 cylinders a day.
Difference between 'best' and 'worst' cylinders was about 0,4 HP.
There were 2 people grinding cylinders daily.
I only did necessary corrections personally.
There were 2 dyno's working every day.
About 300 cylinders were made every year.
And apart of this we also constantly tried to improve HP.
Mostly batches of 30 cylinders were cast, 25 'as before' and 5 with small changes.
Between casting and dynoing took about 3 month's time.
We also dynoed replated cylinders.
They were almost never as good as new one's!

So I would say maybe my guessed numbers might be pretty close.
Putting mine and Raws together we have
Thus far we have using mine and rick information (feel free to add anyone)
In 1988 aprilia made 30 250cc race bikes (First year of the V twin)
In 1989 25 replicas 250's were sold
In 1990 40 250
In 1991......
In 1992 Aprilia sold 40 RSV250's

[Frits Overmars]

Frits, why does the back port (boost port) always need to point upward at an angle. As you said the FOS cylinder has a stable gas flow (plume) even if one port is blocked off. With modern cylinders the transfers are starting to tuck right in under the exhaust, so the transfers could all be arranged as in your FOS cylinder with the rear port having much more effective area because it doesn't have to be at that upward angle?I've changed one of my engines to have a rear port just like a side port, it went very well, perhaps I just thought it went better?

In the FOS cylinder there is a stable axial scavenging column (http://www.kiwibiker.co.nz/forums/sh...post1130452977) centered in the bore, rising up until it collides with the cylinder head.
This collision has two effects. There will be a pressure rise in the head which will slow the flow down; the pressure inside the rising column will rise and the column will expand in diameter, pushing the spent gases that surround it, into the four exhaust ports surrounding the bore.
The second effect of the collision is that the axial column mushrooms in the head and flows down along the walls of the bore, pushing the spent gases that were clinging onto the bore, towards the exhaust ports.
In a conventional cylinder this axial scavenging column is supposed to cling to the rear bore wall. This clinging gives it extra stability and at the same time helps to scavenge the spent gases in that rear area. If the rear transfer port doesn't have that upward angle, it has much more effective area, as you say, so the flow exiting from it can be so much stronger that the axial scavenging column doesn't get a chance to cling to the rear bore wall. The spent gases in that area will no longer be washed out and they have nowhere to go because unlike in the FOS cylinder, there are no exhaust ports in the rear wall of a conventional cylinder.
So although this better-flowing rear transfer port may bring more fresh charge into the cylinder, it may also cause less-effective scavenging, leaving more hot, polluting spent gases in the cylinder. The net result may be positive or negative, depending on your cylinder layout.

Jan Thiel has tested every imaginable port configuration and the Aprilia layout as we now know it was the end result. But things may well be different in your cylinder.
I'd say: reduce the axial angle of the rear transfer port until it does not improve power any more (it will certainly improve piston cooling). And if you overdo it, you can easily increase the axial angle again with some epoxy, or narrow the rear port, which will have a similar effect.

[Frits Overmars]

Blended exhaust, this is what I made for our 6.5cc engine.

Neil, here are some pictures showing the birth of the 1999 MB40 exhaust duct. The first pic shows a points cloud of the duct, from the rectangular blowdown area to the circular duct end, generated by a CFD program that I wrote over 25 years ago, which explains the crude appearance.
The second picture shows a solid, generated by SolidWorks out of that points cloud. The third picture shows one complete copper electrode and a number of cut-up electrodes, used for shaping the inside of the prototype's exhaust duct by means of electro-erosion. The final pic shows the mould for the exhaust duct wax cores.

[Lightbulb]

Thanks Frits, So in the case of the MB LS not sure if it in production yet, is there any restriction and then back up to the header area ?
Nice work, it would have been fairly well the limit of cad software at the time I would think.
With the really wide over the top of the rear transfer port exhaust, how much better or what does that do compared to the narrower port that does not go over the top of the rear transfers ?
Are the rear transfer ports still inclined at 20 deg from horizontal ?
Having the looped shape in the transfer passage, jug handles I call them, what is the advantage as compared to normal model design with just the ports without the curved shape.? Lots of questions I know, just an enquiring mind.
Sometimes very small attention to the right detail makes quite measureable improvements to an engines overall performance.
What material would you recommend for a crank shaft?
Thanks again, Neil

[Frits Overmars]

Thanks Frits, So in the case of the MB LS not sure if it in production yet, is there any restriction and then back up to the header area ?

There is still a tiny unintentional step at the bottom:

With the really wide over the top of the rear transfer port exhaust, how much better or what does that do compared to the narrower port that does not go over the top of the rear transfers ?

That is a damn good question Neil. I had sleepless nights figuring out why that MB engine reacted so differently from other engines. I finally came to the conclusion that this engine needs exhaust gas recycling, although in the case of a two-stroke we'd better call it exhaust gas retention.
The methanol droplets that are added to the inlet air flow, are so coarse, and there is so little time to mix them with the air, let alone let them evaporate completely, that the combustion becomes better when the mixture is pre-heated by some left-behind exhaust gas. So this engine can have too much blowdown time.area. The exhaust port is not as wide as it was in the prototype anymore.

Are the rear transfer ports still inclined at 20 deg from horizontal ?

No; the scavenging column was moving too fast compared to the piston speed of this engine. Aiming the B-transfers more toward each other took some velocity out of that column. Their axial angle is in the region of 10° now.

Having the looped shape in the transfer passage, jug handles I call them, what is the advantage as compared to normal model design with just the ports without the curved shape?

'Normal model design' as in stone age sleeved cylinders, you mean?
The most important part of a transfer port is its inner radius. And this means the smallest radius you can find anywhere in the duct; with a sleeve chances are that there is a sharp edge somewhere, which means: R=0.
Make that inner radius bigger and the port will not only flow better but also better deliver the charge in the direction that you want.

But this was not even the main reason for the sleeveless MB cylinder. In the normal (stone age) model cylinders there is a bronze or alu sleeve with a slip fit in the engine casing, and contact between sleeve and casing leaves something to be desired. And in practice oil will creep between sleeve and casing, so heat transfer from the sleeve to the outside world leaves everything to be desired. The sleeve heats up, and the piston heats up even more because it cannot get rid of its heat.
Then the piston material softens, the crown may collapse unless it is made very thick (and heavy), and the piston fit within the bore that is extremely important with ringless pistons, will quickly deteriorate.

A second improvement was the use of RSP material that retains its strength at high temperatures. A special alloy was developed for the MB pistons and the minimum orderable quantity is such that I'm sure you can have some if you approach Rob Metkemeijer.

What material would you recommend for a crank shaft?

That's a question you should put to Rob; I never concerned myself with the crank. All I contributed was the suggestion to use ceramic balls in the bearings.
The inner race is ground on the crankshaft so we can leave away the inner ring and use a bigger diameter inlet, and we use the cage and the outer race from a normal steel bearing. The ceramic balls cost about 1 € apiece and the bearings live forever.

[seattle smitty]

In Husaberg's thread above quoting Jan Thiel's reminiscences, Mr. Thiel states that re-plated cylinders nearly always made less power than they previously did. Why? Was any way discovered to avoid this? Many racers have to re-plate their cylinders eventually; how should this be done for best results?

[senso]

Maybe when they remove the old plating some "pieces" of the old one are now embedded into the cylinder and cause a higher thermal resistance?

[Lightbulb]

Thanks Frits, alot now makes more sense.
If an engine had the transfer port not go to BDC, but instead were only to about 20 to 30 deg BBDC, are there any negative effects as a result of this?
ie how some engines have astep at the exhaust at BDC, what would happen with the transfers at that same bottom height.
I am still not sure about the porting thing, mainly due to the shifting of the bottom edge as the port effectively as the piston moves past.

The bottom step, do you think this is like an anti reversion step and helps the engine to pipe up and overall easier to run and set a mixture ?

I have seen on model engines where a sleeve that has alot of chrome on it, do not perform as well as a sleeve that only has a very minimal layer of chrome. My take is not only the thermal change, but the amount that builds on the inner edge of the port must be directing the flow enough to be having a negative effect. I did not get onto the port and clean it back out to the original cut shape.
Neil

[Martin1981]

I remember Jan said that when the old worn plating was removed before replating, there was also a little bit aluminium removed (unintentionally and not avoidable?). And Jan said that this is not good.

[Bert]

That's a question you should put to Rob; I never concerned myself with the crank. All I contributed was the suggestion to use ceramic balls in the bearings.
The inner race is ground on the crankshaft so we can leave away the inner ring and use a bigger diameter inlet, and we use the cage and the outer race from a normal steel bearing. The ceramic balls cost about 1 € apiece and the bearings live forever.

Using the steel outer casing and cage is a damn good idea. My little experiment with 100% ceramics didn't quite go to plan... And my neck still hurts from the high side...
I concluded the mess was created by side loading of the bearing (but likely to be wrong).