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

Manuel Rainer a écrit:

Frits did you know why there is only used a 115mm connecting rods in these engines?

No I don't Manuel; I'd have to guess.  Availability perhaps? Or price? Or compatibility with older versions of their engines?

brokedown a écrit:

frits just today i took apart my honda because i have new ideas to try. its T exh port with A/B/C transfers and reeds in the cylinder. but im stumped at the B port. with 15* upward angle it matches the piston dome very well. I dont know the correct term but if the port enter the cylinder flatter then i guess it would let more mixture pass to the cylinder. so if i made B less than 15* (lets say 10*) then perhaps alittle more mixture can make it to the cylinder but it still has no choice except to follow the contour of the piston top. so i dont know what to do here.  did rsa125 B port  angle match piston top ?

If I remember correctly the axial angle of the RSA's B-ports was about 1° steeper than the piston edge angle. And you may want to (re)read this:
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thnx frits   . yes i have read the transfer theory several times.

i think the term i was thinking is cross sectional area. the higher the axial angle, then the less cross sectional area the mixture has as it enters the cylinder. thats how i understand it and hope im right. the reason why higher axial angles work on the A ports is explained in your transfer theory but we can leave that aside for now because im trying to focus on the B ports.

you mention the stream entering the cylinder and colliding with the piston top. " Aiming the transfer ducts axially at about the same angle as the piston dome, usually about 10°, will not cost any effective cross section area and it will noticeably improve the flow coefficient."

so it appears if i use 10* they collide with the piston top slightly, with 15* the stream will match the piston top and inner wall radius can be slightly better but cross sectional area diminishes slightly. this is where im having trouble deciding what to do. and i dont see any clear answer to this situation in your transfer theory .

maybe the engine will run nearly the same with either 10* or 15* ? every question just presents even more questions   

Do what Jan did all his life: build it and test it.

hi frits. i plan to do some tests soon. yesterday i marked some lines on the cylinder with the degree wheel for the timings. what i did is take alot of small pieces of info from this site and applying it to this engine.  today im going to figure out the exh window shape. i have some ideas but im not sure the size limitations of a T style exh port (regarding the total width vs roof arc vs top corner radius). was there some high performance gp engines that used T exh port ? maybe that can give me a general idea what to do with the window

brokedown a écrit:

was there some high performance gp engines that used T exh port ?

All Honda and KTM racing two-strokes.

But no way to find super high blow down big numbers that way   

Frits Overmars a écrit:

brokedown a écrit:

was there some high performance gp engines that used T exh port ?

All Honda and KTM racing two-strokes.

thats strange why they would use T style. because the ktm mx engine had aux exh ports since atleast 25yrs ago.

do you know the honda and ktm engine model name ? so i can locate some photos

have a look frits. i only got alittle done today. but everyday ill do alittle more

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brokedown a écrit:

Frits Overmars a écrit:

brokedown a écrit:

was there some high performance gp engines that used T exh port ?

All Honda and KTM racing two-strokes.

thats strange why they would use T style. because the ktm mx engine had aux exh ports since atleast 25yrs ago.

do you know the honda and ktm engine model name ? so i can locate some photos

RS125 NX4 and NF4 Well just about any GP Honda and a lot of the MX
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Apologies for clogging the Thread with Hondas.....

Ce qui serait lucide, c'est que quelqu'un tente de nous expliquer pourquoi ce post est autant lu.

Je dis cela, je ne dis rien.

  

thnx husaberger thats great pictures  

i have this same condition on the exh port exit. but i didnt grind it !

'Two important points on the exhaust you should NOT modify:
•There is a step between the cylinder and the exhaust, it's absolutely normal !
•There is a restricting convex at the end of the exhaust, don't grind it (loss of 0.5-1 hp !).'     

Hi Brokedown

In 250cc

Honda CR250 2002-2007
TM 250 2002 (I think) - 2014

I don't believe the KTM 250/300 has ever been a centre bridged exhaust. Maybe way back?

Best Regards

Ian  

Frits Overmars a écrit:

brokedown a écrit:

was there some high performance gp engines that used T exh port ?

All Honda and KTM racing two-strokes.

Ian Harrison a écrit:

I don't believe the KTM 250/300 has ever been a centre bridged exhaust.

By racing I meant road racing, not agricultural racing  .

Could you please explain what is the reason that the piston dome pattern at the A B and C transfer ports is the same? On the edge of the piston, all around the piston dome is only a little bit clean although the ports are not opening at the same time and the three ports have different axial angles as well. I'd expect that at the B port the dome becomes cleaner as the port has a narrow axial angle and it opens earlier than the A port.

Excause me if these questions have been discussed earlier, I haven't noticed them.

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Ian Harrison a écrit:

Hi Brokedown

In 250cc

Honda CR250 2002-2007
TM 250 2002 (I think) - 2014

I don't believe the KTM 250/300 has ever been a centre bridged exhaust. Maybe way back?

Best Regards

Ian  

I have yet to find any KTM's with bridged exhaust ports

Institute of TwoStrokes a écrit:

I have yet to find any KTM's with bridged exhaust ports

eg I have a KTM 380 aircooled cylinder, but i can not accurately identify.

Institute of TwoStrokes a écrit:

I have yet to find any KTM's with bridged exhaust ports

KTM didn't want me around their opened engines with a camera (the cylinders were shameless Honda copies) so you'll have to take my word for it:[Vous devez être inscrit et connecté pour voir cette image][/quote]

I could find FRR 125 barrel from one of my computer

Im just building a triple cylinder two stroke jetski engine. They use one pipe for all three cylinders and so It hardly a scavenging effect due to the sonic waves racing every where. In this case due to not having a decent scavenging effect you would think that raising crankcase compression would be more favorable then increasing it as you need the pumping effect. Would I be right in assuming this. Based on this theory I will be running a longer stroke crankshaft to increase my swept volume and further increase the crank case compression. I guess It comes down to I am building a two stroke with out an expansion chamber. there isnt the room to run triple pipes other wise I would be in a heart beat. Please give me your thoughts on this

Frits Overmars a écrit:

KTM didn't want me around their opened engines with a camera (the cylinders were shameless Honda copies) so you'll have to take my word for it

frits i remember someone saying to learn from the people in front of you not from the ones behind. why they (ktm) didnt try to copy rsa125 ?  either purchase a cylinder for duplication or take spy photos  

Just because they left the championship before the Rsa was reaveled to satellites teams   

wax a écrit:

Im just building a triple cylinder two stroke jetski engine. They use one pipe for all three cylinders and so It hardly a scavenging effect due to the sonic waves racing every where. In this case due to not having a decent scavenging effect you would think that raising crankcase compression would be more favorable then increasing it as you need the pumping effect. Would I be right in assuming this. Based on this theory I will be running a longer stroke crankshaft to increase my swept volume and further increase the crank case compression. I guess It comes down to I am building a two stroke with out an expansion chamber. there isnt the room to run triple pipes other wise I would be in a heart beat. Please give me your thoughts on this

A 3-in-1 pipe does have a scavenging effect, although some of it is wasted varying the pressure in the two exhaust branches that are inactive at the time.
What's more: a 3-in-1 pipe can have quite a strong supercharging effect as the exhaust pulse of the cylinder that is just opening its exhaust port, raises the pressure in the branch of the cylinder that is about to close its exhaust port.

OK that makes sense I just needed a better than mine to make sense of it. Thanks for that. So your saying treat like a normal scavenged engine. Thanks again

Frits I was thinking more about the bog standard mx engines going back to the Penton days    I don't think anyone managed any pics even of inside the factory FRR's

I've checked , it's online here ....

hi

Frits or Jan what is the best surface for a con rod? polished, grinded, grinded and than sandblasted, only machined?
how was the RSA cod?

and what was the optimal water temprature for the RSA

thanks Manuel