ESE's works engine tuner

[Flettner]

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.

Makes sense, I just imagined you could massage the plume to be right up the back of the cylinder. FOS it is then.
Although I have got a design that opens a back set of exhaust ports but only at blowdown time then reverts to a tansfer when needed, to keep the cylinder wall acting as a plume guide still.
But the oil less and sleeve engine need to be finished first.

[Frits Overmars]

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.

An exhaust window that does not extend all the way down to BDC may be beneficial in that there is less tendency for the transfer flow to make a U-turn directly into the exhaust. Transfer windows that do not extend down to BDC will have a little less angle.area and the transfer flow may show less tendency to cling to the piston crown once the piston timing edge is below the window floor.

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 ?

A bottom step will somewhat impede backflow, which may only be desirable outside the power band, and it may kick the backflow upwards so it is concentrated against the exhaust duct ceiling. That will make it easier for the backflow to slip over the rising piston and into the cylinder. But raising the whole duct floor will do that too, and even more effectively.

Removing a step, either top or bottom, almost always has a negative effect because in will increase the duct volume. Avoiding steps by way of utilizing adapters, like Wobbly has comprehensively explained here, is recommendable. A small duct volume will help the engine to pipe up. That is one more reason to raise the duct floor.

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.

The thermal influence of the chrome layer thickness is negligible in comparison to the thermal resistance at the transition from sleeve to cylinder and from cylinder to air or to liquid coolant.

The build-up of chrome or nikasil around the port edges is very disturbing to the flow and should be removed. Ideally the port edges should be radiused prior to the plating process and the plating itself should be carried out with an eye on the amperage. A high current means that the plating will take less time, so the performing company will tend to turn the current up, but it will also cause a more severe build-up around the port edges.

[senso]

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).

Is that a DTR engine?
If so they are know for having very,very bad castings and machining, I have seen one that the bearing bores where not aligned, but a couple thousands eccentric, it ate crankshafts lol.

[peewee]

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.

wob mine will look like your pic. have you forgot why i welded ears to the sides of my exh spigot . the spacer (which isnt finished yet) was simply so the aux tunell could have a more gradual transition into the spigot, as the main exh tunell seems unusually short on this engine.

[peewee]

frits i cant recall if i asked you this before but on the rsw drawing it shows the radiuses of all the ports. did you say the radius values were a percentage of the bore diameter ? i want to start making some templates this weekend is why i ask.

example: on the A port inner wall it says near the bottom is R20, middle is R22 and near the top R16. so if the bore is 54mm then these values would represent R20=10.8mm, R22= 11.88mm, R16= 8.64mm ? to apply this strategy to my engine i can simply use these R22, R20, R16 percentages of my bore ?

[Bert]

Is that a DTR engine?
If so they are know for having very,very bad castings and machining, I have seen one that the bearing bores where not aligned, but a couple thousands eccentric, it ate crankshafts lol.

Close, TZR125 but all the same really.

[mr bucketracer]

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).

you gave it to much blow up time

[husaberg]

you gave it to much blow up time

Attachment 314185
He lost his marbles.............Think about it
He must now have rocks in his head.

Anyway MZ's
click on them 3 times

[Frits Overmars]

on the rsw drawing it shows the radiuses of all the ports. did you say the radius values were a percentage of the bore diameter ?

Peewee, the short answer is: no, I didn't. But I suppose you'd rather have the long answer.

example: on the A port inner wall it says near the bottom is R20, middle is R22 and near the top R16. so if the bore is 54mm then these values would represent R20=10.8mm, R22= 11.88mm, R16= 8.64mm ? to apply this strategy to my engine i can simply use these R22, R20, R16 percentages of my bore ?

Let's keep it simple, Peewee. If a radius in any drawing is stated as, for example R20, then it means 20 mm, not some percentage of anything.
Moreover, the RSW drawings that you refer to, were the drawings that I could release at that time; they were not the RSA drawings.
Things have become even simpler since then: in the RSA cylinder the inner walls of the A-ports have one constant radius of 22,6 mm. If you wish to convert that to a percentage of the 54,5 mm RSA stroke (not the bore), be my guest.

There are some radii that I have quoted as being a certain percentage. They are the radius at the top edge of the main exhaust port (6% of the stroke) and the radius at the top edge of a radiused piston (8% of the stroke). But you cannot use these values just like that because they are not simply tangential at both ends, as you can see in the picture of the radiused piston below.

[seattle smitty]

The build-up of chrome or nikasil around the port edges is very disturbing to the flow and should be removed. Ideally the port edges should be radiused prior to the plating process and the plating itself should be carried out with an eye on the amperage. A high current means that the plating will take less time, so the performing company will tend to turn the current up, but it will also cause a more severe build-up around the port edges.

But is this what Mr. Thiel was talking about (in the quote from Husaberg's post)? Presumably he would have known about these issues already, and taken appropriate measures to get the best outcome on cylinders to which he had originally done a lot of hand detailing. In other words, if a racer has a good but worn cylinder, and takes all the precautions you describe, is there any reason the re-plated cylinder won't work just as well as it did originally?

[Frits Overmars]

But is this what Mr. Thiel was talking about (in the quote from Husaberg's post)? Presumably he would have known about these issues already, and taken appropriate measures to get the best outcome on cylinders to which he had originally done a lot of hand detailing. In other words, if a racer has a good but worn cylinder, and takes all the precautions you describe, is there any reason the re-plated cylinder won't work just as well as it did originally?

Well, Jan did take all possible precautions and the re-plated cylinders didn't work just as well as they did originally. So yes, there must be a reason.
Before re-plating the old plating is removed in a chemical bath that seems to eat into the aluminium as well. The cylinders have a more or less porous look when they come out of this bath. They seem to have lost weight and density and apparently they don't like it.

[breezy]

[QUOTE=Flettner;1130886856]Makes sense, I just imagined you could massage the plume to be right up the back of the cylinder. FOS it is then.
Although I have got a design that opens a back set of exhaust ports but only at blowdown time then reverts to a tansfer when needed, to keep the cylinder wall acting as a plume guide still.
But the oil less and sleeve engine need to be finished first

[Haufen]

There are some radii that I have quoted as being a certain percentage. They are the radius at the top edge of the main exhaust port (6% of the stroke) and the radius at the top edge of a radiused piston (8% of the stroke). But you cannot use these values just like that because they are not simply tangential at both ends, as you can see in the picture of the radiused piston below.

Now that's interesting, what's the reason / benefit of them not being tangential at both ends?
Is re-adjustment of the port timings needed after the piston has been radiused? Like dropping the cylinder half of the value of the radius, afterwards? I think such a modification might also behave like a raised barrel, but with the benefit of a better flow coefficient of the ports.

[Frits Overmars]

what's the reason / benefit of them not being tangential at both ends?

For the radius at the top edge of the exhaust port a practical reason is that it would be quite difficult to get it perfectly tangential with the curvature of the cylinder bore. And for both the exhaust edge radius and the piston edge radius, making them completely tangential will not help the flow.
Both pictures below will show that a full tangential piston edge radius would take away so much of the edge that the ring groove would need to be relocated.
With the piston in BDC it would also create a deeper trough between piston and bore which would create turbulence instead of helping the flow cling to the piston crown. And when the piston is half-way in front of the port and the flow is bumping against it, that lower bit of tangential radius won't make a difference, whether it is there or not.

Is re-adjustment of the port timings needed after the piston has been radiused? Like dropping the cylinder half of the value of the radius, afterwards? I think such a modification might also behave like a raised barrel, but with the benefit of a better flow coefficient of the ports.

If you just radius the piston edge, you will increase the port timing and improve the flow. Improving the flow is fine; increasing the timing is not always desirable.
We could drop the cylinder until we have the same angle.areas as before the radiusing, but that does not take the improved flow into account.
What we really ought to do, is include the flow coefficient in the angle.area calculation. But that is beyond the scope of engine simulation programs like EngMod; it would require true 3-dimensional CFD.

[2T Institute]

Frits,
As a non-loaded question, how many 125 RSW and RSA engines were ever produced and what quantities ever got sold to private teams/individuals?

I doubt RSA engines were available over the counter, likewise RSW, a new RSA engine was 130,000 Euro and they chucked in a top of the line 125cc racing motorcycle with it