[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

Jan Thiel a écrit:

Manuel Rainer a écrit:

hi

has anyone a diagram how the powerjet is programmed for the 42 VHTC carburetor in the RSA?


thanks Manuel

I do not have any diagrams Manuel.
The powerjet was closed until about 10.000 rpm.
In was open until 12.500 rpm
After 12.500 it was gradually closed.
a powerjet of 120 was used in combination with a main jet of about 220.
On track the carburation has to be richer, because of the rising airbox pressure.
So you need a different diagram for each gear!

thanks Jan

So the powerjet works only after engine speed? the gas has nothing to do with it?

thanks manuel

Hey guys, I would like to know what do you think about Power porting in engine that have reed valve in cylinder. In Bell book there are only few sentences about it , and he says to cut the piston to get around 200* of opening. Did someone know is there any formula to calculate appropriate degree of opening to get good results or get close to ballpark?

Greetings

Muciek a écrit:

Hey guys, I would like to know what do you think about Power porting in engine that have reed valve in cylinder. In Bell book there are only few sentences about it , and he says to cut the piston to get around 200* of opening. Did someone know is there any formula to calculate appropriate degree of opening to get good results or get close to ballpark?
                                                                                                            Greetings

I prefer boyesenports and a cutout in the pistonskirt. Like this:
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Eventually a window in the piston, but to avoid stiffness issues, I usually do not do that.
Argument: An engine with a reedvalve fitted to the crankcase is also capable to breath free - these are the strongest reedvalve engines...

This is my first post here. I've read all three of these threads with amazement that such knowledgeable people are prepared to offer everything they know to anyone who asks a question. My tuning experience is rudimentary, but my plans now frighteningly ambitious with the wondrous information published here. Like everyone else, I'm so grateful to all contributors, especially Frits and Jan of course.
My question is for anyone to discuss, but obviously I'd like to hear from the Aprilia men if possible. I haven't seen any discussion of this in any of the sections of this thread, but if I've somehow missed it, please forgive me.

What is your opinion or experience of stingers emanating from the belly area of a chamber, rather than from the end of the last baffle conic section as is conventional?
I'm including stingers coming from the side of the belly, as is common in karting, as well as those attached to the final baffle like a normal stinger, but extended inwards so that the inlet point is in the middle of the belly (experimented with by Blair).

Cheers, Roger

It´s a known trick to regulate the noise level , not the best performances system ...)

lodgernz a écrit:

This is my first post here. I've read all three of these threads with amazement that such knowledgeable people are prepared to offer everything they know to anyone who asks a question. My tuning experience is rudimentary, but my plans now frighteningly ambitious with the wondrous information published here. Like everyone else, I'm so grateful to all contributors, especially Frits and Jan of course.
My question is for anyone to discuss, but obviously I'd like to hear from the Aprilia men if possible. I haven't seen any discussion of this in any of the sections of this thread, but if I've somehow missed it, please forgive me.

What is your opinion or experience of stingers emanating from the belly area of a chamber, rather than from the end of the last baffle conic section as is conventional?
I'm including stingers coming from the side of the belly, as is common in karting, as well as those attached to the final baffle like a normal stinger, but extended inwards so that the inlet point is in the middle of the belly (experimented with by Blair).

Cheers, Roger

I never tried this, as this would be a problem on a motorcycle!
What I did try once was a tailpipe sticking INTO the the expansion chamber.
About 10cm.
It made less noise, but also less power.
So it never reached the track!

Jan Thiel a écrit:

luca.lorigiola a écrit:

I have a questio for Mr. Jan.
Have you ever tried to offset the piston pin during RSA engine development?
And, if you tried what was the result?

We used the same piston as the RSW.
This piston had the piston pin offset 1mm in the direction of the exhaust port.

Hi Jan, I was hoping you could explain the difference with these little end pins, is there a performance difference between them ? And if so which one is the better one and at what RPM are these advantages over the STD style pin

Jan Thiel a écrit:

luca.lorigiola a écrit:

I have a questio for Mr. Jan.
Have you ever tried to offset the piston pin during RSA engine development?
And, if you tried what was the result?

We used the same piston as the RSW.
This piston had the piston pin offset 1mm in the direction of the exhaust port.

Hi Jan, I was hoping you could explain the difference with these little end pins, is there a performance difference between them ? And if so which one is the better one and at what RPM are these advantages over the STD style pin

I read some posts on one of the forums you write upon, comments were made about the smaller transfer ports with the superkart engines and EGTs , could you explain this phenomenon please

RAW a écrit:

Jan Thiel a écrit:

luca.lorigiola a écrit:

I have a questio for Mr. Jan.
Have you ever tried to offset the piston pin during RSA engine development?
And, if you tried what was the result?

We used the same piston as the RSW.
This piston had the piston pin offset 1mm in the direction of the exhaust port.

Hi Jan, I was hoping you could explain the difference with these little end pins, is there a performance difference between them ? And if so which one is the better one and at what RPM are these advantages over the STD style pin

Jan Thiel a écrit:

luca.lorigiola a écrit:

I have a questio for Mr. Jan.
Have you ever tried to offset the piston pin during RSA engine development?
And, if you tried what was the result?

We used the same piston as the RSW.
This piston had the piston pin offset 1mm in the direction of the exhaust port.

Hi Jan, I was hoping you could explain the difference with these little end pins, is there a performance difference between them ? And if so which one is the better one and at what RPM are these advantages over the STD style pin

I read some posts on one of the forums you write upon, comments were made about the smaller transfer ports with the superkart  engines and EGTs , could you explain this phenomenon please

 
From 1995 experiments were done with closed piston pins.
First with pressed-in aluminium stops, they gave a power improvement,
but invariably they worked loose. As soon as they touched the cylinder wall you lost power.
The final solution was to have the piston pin closed by welding.
There were 2 solutions: the pin closed and flat, remaining between the circlips.
Another solution was with caps that nearly touched the piston.
There was very little power difference between these solutions!
 
 
The superkart difference in transfer ports is that the Aprilia cylinders were developed using a powerjet.
A powerjet is not allowed in Superkarting.
This stupid rule causes lower exhaust gas temperatures.
To make these temperatures higher you have to modify the exhaust pipe, make it shorter.
And to make the main transfers a little bit narrower.
So less fresh gas is entering the exhaust duct

!! Wow !! , yet again I would not have predicted this but I can see how it happens. It just shows what a finely balanced system an optimal 2T is that your carburation characteristics determine pipe and transfer geometry. I believe, a good 2T tuner will make a phenomenal 4T tuner !!!!!
Jan you are so generous, thanks a million

Jan you mentioned the narrower transfer ports with the non power jet cylinder and the associated EGT values, what was the targeted EGTs for the RSA at the point before the power jet closed and the maximum EGT value reached

Did you ever seek for a EGT value to sit stable or flat on line on the straights or would it always be rising to a maximum target value

Jan Thiel a écrit:

 
The superkart difference in transfer ports is that the Aprilia cylinders were developed using a powerjet.
A powerjet is not allowed in Superkarting.
This stupid rule causes lower exhaust gas temperatures.
To make these temperatures higher you have to modify the exhaust pipe, make it shorter.
And to make the main transfers a little bit narrower.
So less fresh gas is entering the exhaust duct

hi

Jan in which area you have to make the exhaust shorter?
how much lower is the exhaust gas temperatures in a superkart engine?

Thanks Manuel

Manuel Rainer a écrit:

Jan Thiel a écrit:

 
The superkart difference in transfer ports is that the Aprilia cylinders were developed using a powerjet.
A powerjet is not allowed in Superkarting.
This stupid rule causes lower exhaust gas temperatures.
To make these temperatures higher you have to modify the exhaust pipe, make it shorter.
And to make the main transfers a little bit narrower.
So less fresh gas is entering the exhaust duct

hi

Jan in which area you have to make the exhaust shorter?
how much lower is the exhaust gas temperatures in a superkart engine?

Thanks Manuel

Mostly at the front part.
The second question I cannot answer.
I was not involved in the superkart development.

In the straight the values of exhaust temperature increase slightly with increasing revs and show a peak at the instant of closing the throttle for braking.
Reached values ranging from 460° to 510 ° with a peak at 520 ° during a fraction of a second.

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fpayart a écrit:

In the straight the values of exhaust temperature increase slightly with increasing revs and show a peak at the instant of closing the throttle for braking.
Reached values ranging from 460° to 510 ° with a peak at 520 ° during a fraction of a second.

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Francis, good to see your back, I believe you have been a bit ill.
The EGTs you have quoted appear to be very low. Are you being a bit with drawn with your knowledge ?

Francis, good to see your back, I believe you have been a bit ill.
Unfortunately I have to undergo next Monday a little bit tricky surgery of the spine

The EGTs you have quoted appear to be very low.

Are you being a bit with drawn with your knowledge. Sorry, my English level does not allow me to understand your last sentence. Can you rephrase it more simply

Jan Thiel a écrit:

Manuel Rainer a écrit:

Jan Thiel a écrit:

 
The superkart difference in transfer ports is that the Aprilia cylinders were developed using a powerjet.
A powerjet is not allowed in Superkarting.
This stupid rule causes lower exhaust gas temperatures.
To make these temperatures higher you have to modify the exhaust pipe, make it shorter.
And to make the main transfers a little bit narrower.
So less fresh gas is entering the exhaust duct

hi

Jan in which area you have to make the exhaust shorter?
how much lower is the exhaust gas temperatures in a superkart engine?

Thanks Manuel

Mostly at the front part.
The second question I cannot answer.
I was not involved in the superkart development.

Thanks Jan and Francis

Jan with which gas velocity have you calculate the RSA exhaust?
Franchise and with which gas velocity calculate you?

thanks a lot.
Manuel

fpayart a écrit:

In the straight the values of exhaust temperature increase slightly with increasing revs and show a peak at the instant of closing the throttle for braking.
Reached values ranging from 460° to 510 ° with a peak at 520 ° during a fraction of a second.

[Vous devez être inscrit et connecté pour voir cette image]

Thanks for the interesting log! As the exhaust temperatures are rather low, I guess the temperature sensor is located relatively close to the piston? Can you tell us the distance from the piston skirt where the sensor is located?

The sensor is installed in the manifold at 72 mm of the piston.

We never calculated an exhaust. Of course, we start from a model and I make changes with my "feeling" depending on what iI desire. Bench testing allow to make even small adjustments. Today, our exhausts are close to the 102 Aprilia model with some slight modifications: lenght, belly diameter, ajustable stinger

Thank you

And all the best for next Monday!

Francis, désolée d'entendre que tu seras dans les mains des chirurgiens :-(

fpayart a écrit:

Are you being a bit with drawn with your knowledge. Sorry, my English level does not allow me to understand your last sentence. Can you rephrase it more simply

On demande si tu caches des choses...

I've never known Francis to hide things... even when I thought he probably should!

Ha, ha, ha ! it's all in the small details  

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To dissuade you think I'm cheating, here are datas of a real Aprilia GP at Mugello last weekend.
You will notice that the exhaust temperatures are close to ours
Also the signal is a little more dynamic, it is that we use sensor slightly cheaper, bigger in diameter.

Which fuel is used in these logs? Any special race fuel, or could one buy the fuel at the gas station, too?

Special race fuel.
ELF SK35 # MITS41 for the Superkart and ETS ESR GC4 for the bike.

fpayart a écrit:

Ha, ha, ha ! it's all in the small details  

Francis and followers, I was having a small joke, some of you are way to serious, as can well be seen in the superkart thread there are clear photographs of where Francis runs his EGT probes and anyone who has experience with this type of 2t engine knows roughly where the EGTs are,
Francis it must be pleasing to know you have such support, people are ready to bare arms at your defence:happy: