ESE's works engine tuner

[JanBros]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.

aparently Frits already knew this. just found this in a document of him :

aufgrund der Ansaug- und Abgasresonanzen die pro Kurbelwellenumdrehung angesaugte Luftmenge bei einem Wettbewerbsmotor bis zu 40% größer als der Hubraum sein kann

for the non-german speakers :

because of intake and exhaust resonance, in race-engines the amount of air taken in by the egine each turn of the crankshaft can be up to 40% more than it's cylinder volume

[wobbly]

That 1.4 DR is from the RSA - still blows every other race engine out of the water.
Apart from a couple of 250 Superkart , very much clone cylinders , but with later , more developed pipe geometry.
As you would expect.

[jamathi]

That 1.4 DR is from the RSA - still blows every other race engine out of the water.
Apart from a couple of 250 Superkart , very much clone cylinders , but with later , more developed pipe geometry.
As you would expect.

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

[diesel pig]

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

Amazing, I know you were not happy with the exhaust pipe, but to know you thought the inlet was not the best either, I think shows you were right to think there was more power to be had from the RSA.

[jamathi]

Amazing, I know you were not happy with the exhaust pipe, but to know you thought the inlet was not the best either, I think shows you were right to think there was more power to be had from the RSA.

On the dyno we once tested the RSA with a straight and curved exhaust pipe.
The curved pipe gave a little bit less power...
maybe 0.5 HP.
Later it was always tested with the curved pipe..
It might have been better to design the engine with a rear exhaust and the inlet on the front side...
Also, the necessary longer tailpipe needed on the bike cost some power...

[husaberg]

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

When were you given free choice over the pipes?,i seem to remember something about being obliged to use a certain design earlier.
I also seen something i had missed eariler, where either you or Frits mentioned the Reed Derbi had a much larger crankcase volume than the Aprilia.

[diesel pig]

On the dyno we once tested the RSA with a straight and curved exhaust pipe.
The curved pipe gave a little bit less power...
maybe 0.5 HP.
Later it was always tested with the curved pipe..
It might have been better to design the engine with a rear exhaust and the inlet on the front side...
Also, the necessary longer tailpipe needed on the bike cost some power...

Every time you post on the RSA, you open my mind to what could be possible in the future.

[Rudex]

If you widen the boost port on the TM side , and shift the B rear wall over as well , the exit angle would be I believe almost identical to the RSA
but crossing closer to the bore center.
The A rear wall crosses at the same 75% point as the B front and rear. But the A front should be closer to the boost at 78%.
Having each side marked as A and B is confusing things as well, should be RSA and TM.

It would be similar to that:

[wobbly]

Swap the TM A port front/rear wall crossing points - the front wall pointed back the most.

[jamathi]

When were you given free choice over the pipes?,i seem to remember something about being obliged to use a certain design earlier.
I also seen something i had missed eariler, where either you or Frits mentioned the Reed Derbi had a much larger crankcase volume than the Aprilia.

The REED-DERBi had a much smaller crankcase volume than the RSA...

[husaberg]

The REED-DERBi had a much smaller crankcase volume than the RSA...

I think I was thinking this, maybe Frits was referring to intake track volume?

Jan did not enlarge the crankcase volume on the Derbi reed valve engine; it was already big; a reed case has a lot more volume than a rotary valve duct.

I think this was the quote I was looking for last page I think it was from pitlane.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

n theory enclosed cranks are good. Jan Thiel did some experiments at Aprilia with a kart engine that had its reed valve at the front: the incoming mixture had to move against the direction of crank rotation. And although the crankcase stretched over the crank webs, reversing the direction of rotation brought another HP. So the crankshaft does have an influence.
But in practice, if you reduce the distances between crankshaft and crankcase walls to less than 1 mm, the viscous friction of the mixture between the surfaces really costs power at high rpm. And if you make the clearances so tight that lubricating oil can no longer reach the big-end and crankshaft bearings, it will also cost engines
Another negative aspect: any volume with a narrow 'entrance' between the crankshaft and crankcase surfaces acts as an hydraulic damper on the Helmholtz-resonance in the crankcase.
Aprilia has avoided this by making the space between the crank webs as wide as the big-end bearing. As a result the crankcase volume of the 125 cc RSA engine at TDC is about 650 cc,(or 675 maybe) so the exhaust pipe really has some volume to breathe from.
So much for the fairy tale of high crankcase compression

most of this is frits

With the RSA/ RSW Most of the volume is concentrated in the transfer ducts. Then there is the volume inside the piston of course, and the 1 mm shear-avoiding clearance at all surfaces of the crank.
But that is not nearly enough volume. If you take another look at the Aprilia crank below, you will notice that the space between the crank webs is the same as the space needed for the big end bearing. In other words: the crank webs have flat insides, good for another 60 cc or so, if I remember correctly.

Additional benefits: the con rod has an easier time pushing the mixture aside as it moves between the webs, and the big end bearing gets a lot more cooling and lubrication because it is not shrouded in any way.
Because there are no overhung bobweights, the crank webs are stuffed with tungsten to get the balance factor right.
In the RSA125, the con rod was lengthened from the RSW's 115 mm to 120 mm to create even more crankcase volume.

The paddling is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture.
Smooth, full-circle crank webs have the advantage that there is little mixture hiding in nooks and crannies. An example of it's importance: in a certain engine there were 20 mm spaces between the crankshaft bearings and the seals. these ill-accessible volumes acted as pneumatic dampers on the crankcase pressure fluctuation. Filling those volumes with plastic bushes gave a measurable improvement.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

The picture below shows, wait for it, an RSA125-crank with stuffers...
After Jan Thiel went into retirement in 2008, some geniuses at the factory grabbed their chance to 'correct' the errors that Jan left behind, without even testing the result because 'everybody knows the smaller the crankcase volume the better'. But they never could understand why a 2011 RSA125 was slower than a 2007 model (just look at the 125 cc top speeds on any GP-track). O, the joy of working with Italians.....

[wobbly]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.

[Storbeck]

Balance shaft perpendicular to driveshaft? My understanding of what would be needed to balance a 45 degree twin is.....shaky ... But it seems like that could work and that would be super cool.

[wobbly]

I dont understand any of your post Storbeck.
It is a parallel twin - like a Banshee , but fires at 0 - 90*.
The balance shaft is needed to correct the wildly varying primary resultant of one piston being at TDC , as the other is at peak velocity half way up the bore.
Thus it is across the front of the engine with bob weights on each end , one being the drive down to the clutch gear on the end of the crank.
It also happens to have two bevel gears to drive the pair of RV blades - as due to the asymmetric firing you cant have a single large valve operating two ports
like a Rotax snow or water craft that fires at 180*.

[husaberg]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.

As you are going to have to space out the cylinders for clearance with the transfers anyway if it was a supersized sharred single disc with twin ports wouldn't it have a better time area period. Than twin small discs? simplier drive to.
i am thinking like a jetski or snowmobile rotax.