ESE's works engine tuner

[Frits Overmars]

Jan and/or Frits, can you please tell me the Big End Pin and Crank Web Diameter of the RSA 125?

I think the pin was 24 mm but I don't remember the web diameter. Can't look it up either; at the moment me and my files are not in the same country. Jan should know.

[jamathi]

I think the pin was 24 mm but I don't remember the web diameter. Can't look it up either; at the moment me and my files are not in the same country. Jan should know.

The RSA big-end pin was 22mm
On the RSW 21,3 was tried, with one roller more.
It gave slightly less power.
This may have been caused by less crankshaft stiffness or by more friction.
So I don't think 22mm was the best solution....
And the RSW's 20mm never gave trouble!
A 22mm big-end does not guarantee a stiffer crankshaft.
The outside diameter of the crank wheels is just as, or even more, important.
Sorry, I don't remember the RSA crank web diameter.
But I do remember they seriously disturbed inlet flow.
So we had to use a longer connecting rod of 120mm
With hindsight, I consider the RSA a mistake.....
At the time I was too obsessed with the RSW's bad inlet flow, disturbed as it was by the connecting rod...
When the first RSA crankcase arrived at Derbi I immediately did an inlet flow test, of course.
It flowed less than the RSW, I remember feeling VERY disappointed....

[wobbly]

Jan could you elaborate a bit on the inlet flow of the RSA.
I know you tested the kart engine with the shields over the wheels, as these have the inlet flow in the opposite direction
to the top of the flywheels - and that made more power when reversed.
But the RSA had the wheels rotating into the case at the top - ie the same direction as the rear inlet flow.
And I would have thought that the rod would have alot less bad effect on the inlet when moving forward and backward, unlike the RSW
where it moved across the flow direction.
Do you think the shape directly after the rotary valve was " wrong " or was something else interfering with the rear inlet flow into the case.

[jonny quest]

Why did RSA make more power than RSW if inlet flow was down?

[jonny quest]

How did you measure inlet flow? Flowbench, head off, 3 different transfer openings... then averaged

[jamathi]

How did you measure inlet flow? Flowbench, head off, 3 different transfer openings... then averaged

If you do it this way you would only be measuring transfer flow....

[jamathi]

Why did RSA make more power than RSW if inlet flow was down?

There are many more factors in an engine determining power!

[jamathi]

Jan could you elaborate a bit on the inlet flow of the RSA.
I know you tested the kart engine with the shields over the wheels, as these have the inlet flow in the opposite direction
to the top of the flywheels - and that made more power when reversed.
But the RSA had the wheels rotating into the case at the top - ie the same direction as the rear inlet flow.
And I would have thought that the rod would have alot less bad effect on the inlet when moving forward and backward, unlike the RSW
where it moved across the flow direction.
Do you think the shape directly after the rotary valve was " wrong " or was something else interfering with the rear inlet flow into the case.

.

Yes Wobbly, the 'other side' of the cylinder was now like a wall the flow collided with.
Of course many shapes of the duct after the valve should have been tried, but it was not done....
Directing the flow towards the transfer ducts, like in a read valve engine.

My task at Aprilia after I returned from Derbi was cylinder development.
To use a cylinder on the RSA the rear side had to be cut off as much as possible.
As it stood in the way of the inlet flow.
After this cutting such a cylinder gave less power on a RSW and 250
So we did this as least as possible....

And I was not very happy to return to Aprilia, after 1.5 year at Derbi, but had no choice.
So I lost interest, worked very little, and retired the year after.

When I was gone they saw their change to try a 'Honda'-type exhaust duct and port.
They lost 1,5HP, because they had to make the A-ports narrower I think.
What are your thoughts about 'Honda type' vs triple ports?
Have you ever been able to make a honest comparison?
At Derbi I had cylinders with triple ports cast and nikasil plated, they were ready to try when I had to leave....
Still I have some regrets about this.

[F5 Dave]

Life is but so long. I have experiments as yet uncomplete. At this stage unlikely.
But so be it.

Be sure that your sage words are like 20 years just happened in our collective experience.

[husaberg]

Life is but so long. I have experiments as yet uncomplete. At this stage unlikely.
But so be it.

Be sure that your sage words are like 20 years just happened in our collective experience.

An't that the truth.

A friend in Holland has made a 50cc twin-disc.
For the moment it is inferior to the single-disc.
Maybe because of the unequal inlet duct length, caused by the primary drive.
2 22mm carburetors are used.

A few things just occurred to me.
The RSW125 with its single sided entry way have been compromised with its asymmetric flow pattern, but it was also not hampered by the possible slowing down of two opossing intake steams colliding and losing velocity either. Which I assume would happen in a dual sided disc valve set up.
Is a collision of intake streams in a crankcase and slowing down a likely hindrance?
Given the transfers hold enough mixture to fill the cylinder anyway?
I muse maybe for a twin sided disc valve to make a lot more power than a single it would require an intake track with a very large updraft that way some of the airflow would go directly up the transfers on the same side rather than colliding and thus losing velocity in the middle an into the conrod?
I note the kreidler 50 with 2 discs had the intakes facing steeply towards the crankwheels rather than being straight a well. packaging?


In regards to honda percevering with the bridged ex port. (ie old eyebrows)
Cameron wrote in the early 80's that Yamaha knew there flat roofed and colliding stream transfers and reed valve made less power than Aprilia style layout used by Suzuki on the RG500,
but they used it as it gave them greater acceleration and a wider power band within the limitations of their layout, They actually developed a power valve to maximise this effect.
I guess the marketing and corporate gods dictated the use of reed valves as it was a current Yamaha branded product.
I see parallels with the Honda use of the bridged exhaust. It could be said that it was almost a corporate trrademark. used as far back as the Mtr125 and likely further, plus it fitted in with their own patented powervalve design.
It may have ultimately made less power than a triple port, but it might have given a broader power within the confines of what was dictated as a layout Honda was to use.
The same might be said for its much shorter rods.
Ie reed valve single crank.

[adegnes]

Can you go smaller on stinger restriction/venturi size with cooler running fuels like e85?

I'm currently doing sims of my Spx on e85.
50cc, about 27hp with a 15mm diameter, 10mm long stinger restriction. Tubmax peaking at 940.

With Gasoline, 27hp and 15mm stinger restriction does not compute, but how about with e85?

[41juergen]

So based on the output of the EngMod simu I made a first "test" cylinder. The timings are : main ex 198°, aux ex 195° start open, A port 129°, B port 131°, C port 131° CA. That all as a road going bike with the (nozzle) modified stock exhaust (not too bad in the dimensions) at 11000 rpm peak. The question is: are the large aux ex ports the right way to go? Or shall I better use the "tear drop" shape getting a potential better flow with compromising on the (at that engine setup with 56,0mm bore and 50,7mm stroke) already hard to get blow down TA?
The first pic shows the stock setup, the other pics the current status of my porting.

[wobbly]

If you crank up the TuBmax to the same level as petrol, this by inference means that the fuel in the header, and thus the bulk pipe temp
will also change back toward petrol levels - making the pipe wave speed faster.
Alcohol fuels do not loose power when running rich, and being rich allows way higher com without deto.
But this scenario also lowers the pipe temp, due to excess unburnt fuel in the header.
In your video it shows the peak return wave coming back too early ( pipe to short as you said ) but if you run it richer ( and then also try increased com as well )
then the pipe will cool, and make the TL closer to correct - plus it should add some power.

[wobbly]

The big square Aux port will not work well at all.
It will promote bad short circuiting from the A port, and this will also lower the header temp - then trying to lean it down will loose more power.
You have to re arrange the main Ex upper width,or increase the Aux top width to get back the STA without ruining the scavenging regime.
Also,you cannot know for sure that the "reverse stagger " will work in this engine,as the scavenging pattern is heavily dependent upon the B port duct
geometry.
Remember Jans B port duct in the Aprilia was very small in entry area, and you cannot just ignore this when trying to replicate his results.

[adegnes]

If you crank up the TuBmax to the same level as petrol, this by inference means that the fuel in the header, and thus the bulk pipe temp
will also change back toward petrol levels - making the pipe wave speed faster.
Alcohol fuels do not loose power when running rich, and being rich allows way higher com without deto.
But this scenario also lowers the pipe temp, due to excess unburnt fuel in the header.
In your video it shows the peak return wave coming back too early ( pipe to short as you said ) but if you run it richer ( and then also try increased com as well )
then the pipe will cool, and make the TL closer to correct - plus it should add some power.

Thanks!
I'm going to do a few baseline runs on e85 with the unmodified engine, play around with jetting/timing. I'm curious to see how it compares to pump gas on the dyno!