[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

thank you Jan, thank you Frits

Hello Frits,
Thanks for last answer, and sorry for delay !
[quote="Frits Overmars"][There is a method to minimize the influence of the tailpipe length: place a restrictor between the endcone and the tailpipe, and give the tailpipe a clearly bigger diameter than the restrictor. On the exhaust concept below you can see what I mean. D5 is the restrictor diameter and D6 is the tailpipe diameter./quote]
Ok I understand, but, when you say "Taipipe clearly bigger" you mean as big as 2 mm for exemple ? I saw 125GP and I was surprised by taipipe and silencer diameters ! What whoud be a good ratio between silencer pipe and tailpipe diameter ?
Stéphane

I think you'll find your answer in Frits' FOS exhaust concept a some posts back.

Hello Jan,
Thanks for help
I had saw Frits' FOS Exaust concept, which is very well -of course- , but I thought it was general trend for "begining tuners" -I may haven't understood : Frits, sorry for that in this case-, and I was wondering to Frits for 125 GP like Aprilia RSA or RSW exaust ; Maybe it's the same answer, but I'm not sure, it' s why I asked him ! I may have badly explain ! (and your're right..., I have probably to read back to see 125GP silencer answer Embarassed )
Stéphane

Mr.Jan and Mr.Frits don't know if this was done and if it still has this information, what is the weight of the complete aprilia RSA engine and the weight of the individual components, pistons, connecting rod, crankshaft ...

And please, can you start a new production line ???
125 single, 250 twin, 500 4 and why not 750 6 ???

Good evening everyone, I have another stupid question: I see that there's a company ad for covering the piston top area with ceramic coating for reducing the heat transfer from the combustion chamber (they claim a 15% reduction).
Did any of you test this? Is this really interesting on a perfomance point of view?

carlovitch1 a écrit:

...there's a company ad for covering the piston top area with ceramic coating for reducing the heat transfer from the combustion chamber (they claim a 15% reduction). Did any of you test this? Is this really interesting on a performance point of view?

The coating prevents heat transfer from the combustion into the piston material, so you should think it would make the piston very happy.
But because of this reduced heat transfer the coating surface stays very got, much hotter than a piston dome without coating would be.
And this hot surface provokes detonation: no happy piston and no happy rider

I suppose it also reduces the cooling ability of the incomming fresh mixture at BDC, so again not good ?

OK, thanks Frits and Jan for quick replies. Looks like this company just tries to sell ceramic coating (they do for all sorts of things) without seriously studying the question.

Happy Birthday Jan !

Muchas felicidades Jan, gracias por compartir tu conocimiento.

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Happy Birthday Jan Thiel!

Happy Birthday to you Jan !

To Jan Thiel!
All the best and many more carefree years!

Tanti auguri Jan Thiel il mago dei motori

Gelukkige verjaardag Jan

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Thank's for the birthday wishes!!!!!!!!!

Frits or Jan and who else can help experiments with different materials for connecting rod bearings

Hi Jan and Frits. I posted the following on Kiwibiker but thought I may get more insight from the Aprilia viewpoint at least on here.

I have my 3D printer up and running and am continuing on with my snowmobile drag racing cylinder development project. My hope is to design and build a cylinder using the best design features of proven high output engines, notably the Aprilia RSA and Wobbly's further development from there. There are some design parameters that have to be taken into account. My plan right now is to build a 508cc twin with a bore and stroke of 68 X 70mm. If this produces good results an inline four cylinder of 1016cc would follow. I have tentatively chosen a Honda CR250R flat top piston and would move the ring locating pin to the centre of the c port. The 70 mm stroke was chosen because it is stock in a couple of manufacturer variations and allows close to a square engine at the displacements I am interested in. This setup would target max HP at 9500 RPM and due to the use of a CVT belt drive system which will hold the engine at peak power RPM throughout the run requires no overrev power. Snowmobile engines are conventionally inline twin or triple cylinder designs with the intake on the back side of the engine and the exhaust exiting forward. I will be using stock crankcases and crankshafts and this limits the width of the cylinder. In my case the base of the cylinder is approximately 137.5mm wide. I have scaled up and printed an RSA cylinder at a 68 mm bore and unless I have screwed up, which is entirely possible, the base of this cylinder is approximately 173mm wide. Obviously, I do not have the room to include the large sweeping radii of the transfer passages of the Aprilia cylinder. I have attached a couple of pics to hopefully clarify the situation. I can design the exhaust port and ducting and transfer ports themselves inline with Frits' FOS calculations but am concerned that the transfer passages will be a limiting factor. What is the minimum radius that I can get away with? Or am I fighting a losing battle?

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polcat88 a écrit:

Hi Jan and Frits. I posted the following on Kiwibiker but thought I may get more insight from the Aprilia viewpoint at least on here.
I can design the exhaust port and ducting and transfer ports themselves inline with Frits' FOS calculations but am concerned that the transfer passages will be a limiting factor. What is the minimum radius that I can get away with?

The reactions on the Kiwibiker forum may be of interest to the Pit-Lane readers, so here is a link:
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Your question: "What is the minimum transfer passage radius that I can get away with?" is a typical example of a simple question for which there is no simple answer. Flattening the transfer ducts will no doubt cost power, but I cannot give you a simple relation between the rate of flattening and the rate of power loss.
Moreover, I'd have to guess as to your definition of "getting away with".  Would you be happy with 95%, or 75%, or even less power?
If you wish to stick to (or are obliged to stick to) the center distance between your cylinder bores, all you can do is try. Or, like Wobbly suggested on the Kiwibiker forum, reduce the bores in order to gain room for the ducts.

Frits. Allow me a question.
The balance shaft of RSA, its function is to eliminate vibrations right?
Does it also help to increase engine horses?

The Garelli 125-1 had a balance shaft.
Without it the engine gave 1,8 HP less
The RSA was, of course, never tested without balance shaft