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

Sujet: Primary gear ration Lun 18 Nov 2013 - 17:31

Question for Jan and Frits

What primary gear ratio would be ideal for a 250cc 2 cylinder engine?

Fast rotating gearbox would have less torque load on the gear but I guess also higher power loss?

Rotax 256 22:58= 2.6364
Rotax 258 32:77= 2.4063
PVP252 26:58= 2.2308
DEA SK251 std. 21:55= 2.619
DEA SK251 opt. 22:54= 2.4545
RSA125 23:70= 3.0435
RSW125 27:68= 2.5185
BRC250 22:58= 2.6364

Is it something you can measure on a dyno or will it only make a difference on the track?

Do you really think they have divination abilities ?

Mic a écrit:: Question for Jan and Frits

What primary gear ratio would be ideal for a 250cc 2 cylinder engine?

Fast rotating gearbox would have less torque load on the gear but I guess also higher power loss?

Rotax 256 22:58= 2.6364
Rotax 258 32:77= 2.4063
PVP252 26:58= 2.2308
DEA SK251 std. 21:55= 2.619
DEA SK251 opt. 22:54= 2.4545
RSA125 23:70= 3.0435
RSW125 27:68= 2.5185
BRC250 22:58= 2.6364

Is it something you can measure on a dyno or will it only make a difference on the track?

The slower the gearbox turns, the less the friction loss is!
So in this case the RSA would be the best, and the PVP the worst.

Jan Thiel a écrit:

Mic a écrit:: Question for Jan and Frits

What primary gear ratio would be ideal for a 250cc 2 cylinder engine?

Fast rotating gearbox would have less torque load on the gear but I guess also higher power loss?

Rotax 256 22:58= 2.6364
Rotax 258 32:77= 2.4063
PVP252 26:58= 2.2308
DEA SK251 std. 21:55= 2.619
DEA SK251 opt. 22:54= 2.4545
RSA125 23:70= 3.0435
RSW125 27:68= 2.5185
BRC250 22:58= 2.6364

Is it something you can measure on a dyno or will it only make a difference on the track?

The slower the gearbox turns, the less the friction loss is!
So in this case the RSA would be the best, and the PVP the worst.

3.0435/2.5185 = 1.21 = 21% more power loss.
When RSA power loss is 4.3% than RSW = 5.1%
RSA 54hp *(100%-5.1%)/(100%-4.3%)= RSW 53.5hp

LucF a écrit:

Jan Thiel a écrit:

Mic a écrit:: Question for Jan and Frits

What primary gear ratio would be ideal for a 250cc 2 cylinder engine?

Fast rotating gearbox would have less torque load on the gear but I guess also higher power loss?

Rotax 256 22:58= 2.6364
Rotax 258 32:77= 2.4063
PVP252 26:58= 2.2308
DEA SK251 std. 21:55= 2.619
DEA SK251 opt. 22:54= 2.4545
RSA125 23:70= 3.0435
RSW125 27:68= 2.5185
BRC250 22:58= 2.6364

Is it something you can measure on a dyno or will it only make a difference on the track?

The slower the gearbox turns, the less the friction loss is!
So in this case the RSA would be the best, and the PVP the worst.

3.0435/2.5185 = 1.21 = 21% more power loss.
When RSA power loss is 4.3% than RSW = 5.1%
RSA 54hp *(100%-5.1%)/(100%-4.3%)= RSW 53.5hp

Yes, OK Luc, thank you!
But the RSW also gave 54HP.
Does this mean it was actually better?
I think so!

Dernière édition par LucF le Ven 22 Nov 2013 - 13:46, édité 3 fois

Absolutely Jan, there's no doubt about it. PVP is worst with 5.8% almost 0.9 hp less.
The load on the gearbox will be greater, so in other cases it may be interesting to do the reverse, consider the Aprilia 500twin.

This is new IAME KZ 125 cylinder... aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 809262

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 809262

For me, is more similar at Aprilia.... lol!

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Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

LucF a écrit:: Absolutely Jan, there's no doubt about it. PVP is worst with 5.8% almost 0.9 hp less.
The load on the gearbox will be greater, so in other cases it may be interesting to do the reverse, consider the Aprilia 500twin.

Luc, the power loss on the PVP is higher due to faster spinning gearbox, but the torque load on the gears is lower because torque is directly releated to rpm. Same power with higher rpm = less torque.

Mic a écrit:

LucF a écrit:: Absolutely Jan, there's no doubt about it. PVP is worst with 5.8% almost 0.9 hp less.
The load on the gearbox will be greater, so in other cases it may be interesting to do the reverse, consider the Aprilia 500twin.

Luc, the power loss on the PVP is higher due to faster spinning gearbox, but the torque load on the gears is lower because torque is directly releated to rpm. Same power with higher rpm = less torque.

Yes Mic, that is right.

Jan Thiel a écrit:: ....the RSW also gave 54HP. Does this mean it was actually better?

Maximum power values of the RSW and the RSA are virtually identical. But the RSA clearly has a better power curve.
For instance, at 11.000 rpm the RSA produces 6% more power than the RSW. This cannot be explained by the small difference in transmission efficiency.

The RSA really is a different engine, and not only with regard to the inlet flow. The exhaust pipe is different, the cylinder head with its two extra bolts is different, and so on. All these factors play together and I don't think it is possible to draw conclusions regarding the effect of one single factor like a difference in primary transmission ratios.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

everybody happy holidays aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 771973

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 771973

. hi jan and frits. thnx again for sharing your knowledge its the best i've seen anywhere. what im trying to do is use logical thinking and apply it to other engines. right now i have several different engines im working on and this is one engine. what do you think of it or maybe i missed something and can make it even better ? left side is what is how i plan to change the transfer ports with epoxy. right side is standard from the factory. thnx again for anybody that gave real good information here aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 241515

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 241515

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Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

Frits Overmars a écrit:

Jan Thiel a écrit:: ....the RSW also gave 54HP. Does this mean it was actually better?

Maximum power values of the RSW and the RSA are virtually identical. But the RSA clearly has a better power curve.
For instance, at 11.000 rpm the RSA produces 6% more power than the RSW. This cannot be explained by the small difference in transmission efficiency.

The RSA really is a different engine, and not only with regard to the inlet flow. The exhaust pipe is different, the cylinder head with its two extra bolts is different, and so on. All these factors play together and I don't think it is possible to draw conclusions regarding the effect of one single factor like a difference in primary transmission ratios.

I remember Jan writing the RSW were one time also tested with the APF cylinder and then it made the same 54hp as the RSA.

But of course there was still a lot of differences between them even with the same cylinders on them.

Would like to see Thijs finishing his dual side disc engine. Perfect intake flow and straight exhaust.

Nombre de messages : 55 Localisation : Germany Date d'inscription : 20/02/2012

brokedown a écrit:: everybody happy holidays . hi jan and frits. thnx again for sharing your knowledge its the best i've seen anywhere. what im trying to do is use logical thinking and apply it to other engines. right now i have several different engines im working on and this is one engine. what do you think of it or maybe i missed something and can make it even better ? left side is what is how i plan to change the transfer ports with epoxy. right side is standard from the factory. thnx again for anybody that gave real good information here

This change will work fine I think. But I'm not sure if one can trust epoxy permanent at such locations. What kind of epoxy do you use? (manufacturer)

Could someone expand on this gearbox efficiency question? Saying losses are proportional to rotational speed seems too simple: that would be true if the friction forces were constant, but it might be reasonable to suppose they are proportional to the torque... in which case it all cancels out. And greater torque might require wider or larger diameter cogs... aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 55116

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 55116

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

Daniel A. a écrit:: This change will work fine I think. But I'm not sure if one can trust epoxy permanent at such locations. What kind of epoxy do you use? (manufacturer)

yes i think the change will work good. atleast alot better than what it is now. i dont think the sharp hooks in the corners is a good idea. besides maybe its not the best idea to have the B port pointing at the C port. i think i will try the green stucco epoxy like jan mentioned. maybe ill try devcon also. really i dont have much epoxy experience so i dont know what is best

Hi Guys

My thoughts are exactly the same as GrahamB regarding the primary drive ratio change. I believe the differences in power lost at the output shaft between the ratios listed would be very, very small (if anything). other considerations surrounding that selection might well have more significance.

Brokedown, For experimenting with port shapes we use Devcon F Aluminium Putty. It's certainly readily available in the USA, just "google" it. Be careful to check the use by date, don't accept any that has gone past, keep it in a cool reasonably constant temperature.

Thanks for the "holiday wishes", but I think "Thanksgiving" is a purely US holiday aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 2878

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 2878

Best Regards

Ian

Sujet: Devcon F Dim 24 Nov 2013 - 10:22

Devcon F is certainly a fantastic substance and got me out of the shit on several occasions when I was racing TZ750 Sidecar's in the 80's. In the right situation it was a much better solution than welding.
Some might think it a bodge up but for the hard up National racer it was a life saver. aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 771973

GrahamB a écrit:: Could someone expand on this gearbox efficiency question? Saying losses are proportional to rotational speed seems too simple: that would be true if the friction forces were constant, but it might be reasonable to suppose they are proportional to the torque... in which case it all cancels out. And greater torque might require wider or larger diameter cogs...

The frictions on the gearbox are indeed not constant so we express these in percentage of the power and not in hp.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

hey mates today from ebay i got the green stucco putty and devcon F putty. so i can try both kinds aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 771973

let me ask one more question to anybody with methanol experience. i wont bore you with details but one engine i have uses methanol but i have a feeling the head geometry is not right. when cutting the head dimensions for methanol is there any general rules to follow that would atleast get it close to the ballpark, then after that i can use the cut and try method to find the very best results ? like what frits said about the 1% of stroke for the piston to head clearance. would that also apply to methanol ? do i also want the squish paralell with the piston ? width 50% of bore area ? i suspect the transition from squishband to combustion chamber should always have zero radius for all types of fuel. thnx guys if you can help a junior tuner like me aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 241515

Brokedown, my limited experience with methanol on a two-stroke is that you can keep the head 100% identical with a petrol head.
What I learned the hard way: do not try to correct a wet spark plug by jetting leaner when running on methanol. The engine will seize before the plug comes out dry.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

before i converted my bike to methanol everybody said its real easy to tune but since ive been using the methanol ive found its not very easy to tune. but i dont have alot of experience with it yet so perhaps in more time i can figure it out. i remeber the first time i used it frits. accidentaly i had the carb floats upside down and it was pushing huge amounts of methanol into the cylinder (im using fuel pump) and would hardly run. there was maybe 1 gallon in the tank and when that ran out the engine went lean and immediatly i got about 10hp extra aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 809262

also i didnt tune it for a dry plug. mostly i was looking at the base of the plug and if it was burning any of the plating off. that was by advice from other people but im not sure if thats the correct tuning procedure. anyways methanol seems rather strange. it shoots raw fuel out the pipe but still seems to run ok. perhaps because you put about 2x more fuel in the cylinder than gasoline ?

brokedown a écrit:: ... methanol seems rather strange. it shoots raw fuel out the pipe but still seems to run ok. perhaps because you put about 2x more fuel in the cylinder than gasoline ?

2,26 times as much, to be exact. Which means that you will need to pay attention to your complete fuel system:
tank ventilation, fuel cock flow, filter flow and, often forgotten, float valve seat diameter. And jetting, of course.

brokedown a écrit:: before i converted my bike to methanol everybody said its real easy to tune but since ive been using the methanol ive found its not very easy to tune. but i dont have alot of experience with it yet so perhaps in more time i can figure it out. i remeber the first time i used it frits. accidentaly i had the carb floats upside down and it was pushing huge amounts of methanol into the cylinder (im using fuel pump) and would hardly run. there was maybe 1 gallon in the tank and when that ran out the engine went lean and immediatly i got about 10hp extra

also i didnt tune it for a dry plug. mostly i was looking at the base of the plug and if it was burning any of the plating off. that was by advice from other people but im not sure if thats the correct tuning procedure. anyways methanol seems rather strange. it shoots raw fuel out the pipe but still seems to run ok. perhaps because you put about 2x more fuel in the cylinder than gasoline ?

Tuning for methanol seems to be just drill the main jet out to whatever small drill size is handy , emery the needle down and set the stator to full advance. lol!

One thing that is VERY important with methanol is to give the engine a nice 'petrol wash' at the end of the day straight after the final race. Connect a small drink bottle of a rich petrol/oil mix and rev it and let it blubber away untill all that methanol is gone. Will be curtains for your engine internals if you let methanol stay in the cases/carburetor

Sujet: Exhaust shape Sam 30 Nov 2013 - 10:25

Question for Jan and Frits

I can see the exhaust of the lower cylinder of the RSW/RSA250 has a straight section first and then a quite sharp bend.

Is this better than a long smooth bend? It looks like there is enough space for a smoother shape but perhaps it's important to keep the first section as straight as possible?

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Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

Frits Overmars a écrit:

brokedown a écrit:: ... methanol seems rather strange. it shoots raw fuel out the pipe but still seems to run ok. perhaps because you put about 2x more fuel in the cylinder than gasoline ?

2,26 times as much, to be exact. Which means that you will need to pay attention to your complete fuel system:
tank ventilation, fuel cock flow, filter flow and, often forgotten, float valve seat diameter. And jetting, of course.

installing the fuel system was the easy part. getting the engine tuned has proved more difficult for me. im not sure of the ign curve but the stator is set to 16* BTDC. i have only advanced it a couple degrees so far. its winter now so next spring in warmer temperature ill tune it more. but in the meen time ill port a new cylinder from all the great info in this forum aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 23 771973

tank ventilation is enlarged to 3/8" (9.5mm) ID.
fuel valve is 3/8" (9.5mm) in and 5/16" (7.9mm) out.
high flow filter 3/8" (9.5mm) in/out
65 liter per hour fuel pump
48mm carb with 2 power jets
16:1 castor oil mix
i purge the full system with gas afterwards
this is my album for the sytem if you want to look

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