[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

jfn2 a écrit:

Frits or Jan:
Hello. In designing the exhaust ports why did you raise the main port opening to 202° instead of raising the sub exhaust ports to the same height of the main exhaust port and/or squaring the sub exhaust ports instead of a triangle shape to get more blowdown angle area? Which leads me to ask why are the sub exhaust ports in a triangle shape?
Thank you. Jeff

Jeff, the dimensions of the subports were very carefully determined.
Never removing more than 0,25mm at a time.
Making them as high as the main port costs a lot of midrange power.
And you have to keep them as far away from the transfer ports as possible.
So this is why they have a triangular shape.

motoholic71 a écrit:

Hi I recently registered here very motivated by the warm and most inspiring participation of Frits and Jan,and have to say it's been a pleasure and very elucidative reading,just finished 1st part.
I'm also hopelessly addicted to the smell of 2 stroke oil fumes seasoned with the sent of burnt rubber on asphalt and clutch dust, very early in cold sunny mornings
Excuse me,I also can only write in Eng but usually get the gist of Fr sentences.
I'm an electronic technician and am building a deto detect, test showed very strong signal with this very simple arrangement and a wide band automotive Bosch sensor,even got the sensors picking up signal from the opposite cylinder,but is important to have good surface contact,be the closest to the comb chamber and no inclination (0 deg) and in my case the sensor is seeing all the head nut torque which I could keep "low(er)" thanks to "o"ring sealing instead of head gasket
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Please excuse the off topic,I also would like to ask things about the Aprilia and Frits and Jan time there,but I respect if they are tired of so many questions and can't reply,plus I have yet to read many pages and might be revisiting subjects.

Mr Frits and Mr Jan I trust you were present at the track on race or practice sessions close by to other competitor teams,did you interact with them?Was there a friendly atmosphere between teams? Was there anyone caught trying to spy or suspect to steal secrets?

Why is the RS carburettor mirror polished?If it's to aid flow why not do the same to the engine internals,or the purpose is another?
Why was Porsche design the gearboxes if they're a car company,when clearly there are motorcycle manufacturers in constant development that should do better?
In the pursuit for the last Hp, was the rider's feedback quickly passed to you(s) when a change was track tested?
Did you ever have conflictive results like the rider saying "worst" and the machines saying "better" in face of a new change?If so how was this decided?

since I'm here Just 1 more very quick off topic (for me to anyone with sound knowledge):
dealing with a wet clucth in road racing is it worth to polish the clutch basket surface to reduce oil drag?

Thank you All this is great!!Keep it going forever

I fully agree with you about the detonation sensor position.

I never visited races or practice sessions, because after 20 years of visiting races I started to hate travelling.
Also the friendly atmosphere that once existed ended a long time ago.
Photographers now act as spies!

Polishing does not aid flow.

Porsche, apart from making cars, does a lot of development for others.
So the Derbi gearbox was designed by them and also the Derbi's aerodynamics!
The Derbi design team was too small to do this themselves.
Not even the engine was designed by Derbi.
It's design was stolen from Yamaha by Harald Bartol.
Only the later RSA engine was designed by Derbi.
And later taken over by Aprilia.

Most of the time the things that went well on the dyno also went well on track.
But ultimately the rider decides.

Jan Thiel a écrit:

genna900 a écrit:

hi
my name is Danny are appassionated of two stroke engine, I want make an question, why the radius down of exhaust duct of the cilinder follow the radius of piston dome? what is the function in that configuration? sorry for my english
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The radius of the exhaust duct does NOT follow the piston radius!
Instead the volume of the exhaust duct was reduced as much as possible.
This improved flow, as seen on the flowbench.
And above all, it improved blowdown!

thanks for the answer.
not understand where is need reduce volume.
Mr Thiel Could be more precise?
In that section what is the best shape for improve the flow ?

Jan or Frits or Both?

Jan has mentioned that one of the things you would want to do is a twin disk valve arrangements.
I think he either ran out of time or the "Great Leader" did not approve

I have seen a couple of set ups can you think of an eligant solution for a tandem twin set up?

I have seen a twin disk set up on the Exactweld but it appears the crankshafts did not counter rotate.
The only ways i can think of is with a chain or belt drive. But i suspect i are missing the obvious solutions

With the variable disk/ throttle with in crankcase fuel injection setup Uniflow posted i imagine see it could be very slim indeed. Not to mention the advantages in drivabilty and it seems very crisp fueling with the fuel injection that neil has made from commonly anailabe car components

I hope neil doesn't mind me posting the aditional pics as they were already on the web

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Thank you so much Mr Jan for your time.I wish you could have worked without budget limitations...

genna900 is the shape you're asking? what I think after reading this topic is don't enlarge the exhaust duct but if you really have to, don't touch the top and bottom of the duct,but maybe I'm wrong

Hello

jan or frits can you tell me the reason why the outlet has the edge like in the foto and what was the improvement from this?


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thanks Manuel

The idea behind this was to avoid hot exhaust gases reentering the cylinder.
There was not much difference in HP.
Making the cylinder exit wider gave about 0,8HP more.

husaberger a écrit:

Jan or Frits or Both?

Jan has mentioned that one of the things you would want to do is a tin disk valve arrangements

I have seen a couple of set ups can you think of an eligant solution for a tandem twin set up?

I have seen a twin disk set up on the Exactweld but it appears the crankshafts did not counter rotate.
The only ways i can think of is with a chain or belt drive. But i suspect i are missing the obvious solutions

With the variable disk/ throttle with in crankcase fuel injection setup Uniflow posted i imagine see it could be very slim indeed. Not to mention the advantages in drivabilty and it seems very crisp fueling with the fuel injection that neil has made from commonly anailabe car components

I hope neil doesn't mind me posting the aditional pics as they were already on the web

<img src="http://t1.gstatic.com/images?q=tbn:ANd9GcRbjhiV5CIatSaOChqbmjeSQ57kARQwNJi0LLaV4ambJpa5prSr4BTNw9PM" width="375px"/><img src="http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=262900&d=1335660247" width="350px"/>
<img src="http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=262898&d=1335660286" width="340px"/><img src="http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=250811&d=1321437680" width="380px"/>
<img src="https://2img.net/h/i1056.photobucket.com/albums/t380/uniflow/c0231e31.jpg" width="360px"/><img src="https://2img.net/h/i1056.photobucket.com/albums/t380/uniflow/0c93ef14.jpg" width="360px"/>
<img src="https://2img.net/h/i1056.photobucket.com/albums/t380/uniflow/3dfc14da.jpg" width="360px"/><img src="https://2img.net/h/i1056.photobucket.com/albums/t380/uniflow/1f6c55fd.jpg" width="360px"/>

I think a twin disc on a tandem is impossible because of the necessary coupling gears.
That is why the Exactweld engine is not contrarotating.
Probaby it has bad vibrations.

Fuel injection was tried by many people.
The problem was always the driveability!
HP was slightly better.
At least that was the experience at Aprilia.

genna900 a écrit:

Jan Thiel a écrit:

genna900 a écrit:

hi
my name is Danny are appassionated of two stroke engine, I want make an question, why the radius down of exhaust duct of the cilinder follow the radius of piston dome? what is the function in that configuration? sorry for my english
[Vous devez être inscrit et connecté pour voir cette image]

The radius of the exhaust duct does NOT follow the piston radius!
Instead the volume of the exhaust duct was reduced as much as possible.
This improved flow, as seen on the flowbench.
And above all, it improved blowdown!

thanks for the answer.
not understand where is need reduce volume.
Mr Thiel Could be more precise?
In that section what is the best shape for improve the flow ?

The objective was to strengthen the pressure fluctuations in the exhaust duct.

Jan, why was there problems with drivability? EFI is good at smoothing out the bottom to mid range. Where were the injectors situated on your tests? At the throttle body?

uniflow a écrit:

Isn't it interesting, same set up as I have planed for the YZ 250 accept I'm fitting the injectors to the rear two ports. Same injecting down on to up comming air. I'm waiting on my drum throttle body housing to arrive back from Heat Treatments ( cast in CC601 ). I'll post a picture if you like.
What charging system are you using, how many amps, at what rpms?

Yeah I'd like to see it.

I bought a WR250 stator and flywheel. I took and drilled the hub out of the KX500 flywheel and fit it to the WR250 flywheel. The stator is wired for both AC and DC originally however it is possible to rewire it so that it is just DC. This gave 130 watts of charging power. I don't remember the amperage vs. RPM off hand. I can tell you that throughout the entire time I was testing the charging system always had plenty of juice to power the system. The only time I had trouble with power was when I was making a lot of changes to the bike over a long period of time with the engine off just using the battery. The battery itself is composed of A123 lithium ion cells wired together to give around 13.2 Volts. It hardly takes up any room and is very light. I will definitely be doing something similar for my new system.

Unless I'm mistaken, it seems that the EXACTWELD is well a contra-rotating engine, as shown in this picture

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fpayart a écrit:

Unless I'm mistaken, it seems that the EXACTWELD is well a contra-rotating engine, as shown in this picture

You are quite right (as usual), Francis .

Jan Thiel a écrit:

The idea behind this was to avoid hot exhaust gases reentering the cylinder.
There was not much difference in HP.
Making the cylinder exit wider gave about 0,8HP more.

I know the answer to this was in the first topic. But why not making a round exhaust flange bigger than a round exit from cylinder.

For example using a ending round duct of 38mm getting in one 41mm round exhaust flange. So we would have a kink of 1,5mm stoping burned gases.

Did you try the difference, Romeuh? Jan did....

fpayart a écrit:

Unless I'm mistaken, it seems that the EXACTWELD is well a contra-rotating engine, as shown in this picture

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

I see this is a quad disc inline twin, but does anyone have any further pictures or suggestions on how such an arrangement may be configured ,

Jan maybe you could advise the followers on what you would have liked to try if you we're going to attempt such a system ?

RAW a écrit:

....................

Jan maybe you could advise the followers on what you would have liked to try if you we're going to attempt such a system ?

+1 although,better late then never,it would be nice to start another thread on two stroke development so the masters and more
experienced on them can share their knowledge and keep this thread on the RSW/A 125 and the people behind it.

XpTpSMTT a écrit:

...it would be nice to start another thread on two stroke development so the masters and more experienced on them can share their knowledge and keep this thread on the RSW/A 125 and the people behind it.

My experience with forums is that 'trying to stay on topic' never works. Besides, I have seen some beautiful ideas presented here that I would not have missed for the world. And how would you limit access to the 'more experienced'? We all have to start somewhere....

I must admit I have been thinking about a website of my own, mainly because I am active on several forums and I keep forgetting where I posted what, so I have to constantly search and repeat....
That being said, I realize I am too pressed for time (or maybe too lazy) to run my own website, and I am quite happy on Pit-Lane. And I suppose so is Jan.

RAW a écrit:

fpayart a écrit:

Unless I'm mistaken, it seems that the EXACTWELD is well a contra-rotating engine, as shown in this picture

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

I see this is a quad disc inline twin, but does anyone have any further pictures or suggestions on how such an arrangement may be configured ,

Jan maybe you could advise the followers on what you would have liked to try if you we're going to attempt such a system ?

Google is your best ali

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Frits Overmars a écrit:

XpTpSMTT a écrit:

...it would be nice to start another thread on two stroke development so the masters and more experienced on them can share their knowledge and keep this thread on the RSW/A 125 and the people behind it.

My experience with forums is that 'trying to stay on topic' never works. Besides, I have seen some beautiful ideas presented here that I would not have missed for the world. And how would you limit access to the 'more experienced'? We all have to start somewhere....

I must admit I have been thinking about a website of my own, mainly because I am active on several forums and I keep forgetting where I posted what, so I have to constantly search and repeat....
That being said, I realize I am too pressed for time (or maybe too lazy) to run my own website, and I am quite happy on Pit-Lane. And I suppose so is Jan.

Yes,it never works....
Limit?of course not!!but to distinguish between two different things,the (his)story of the aprilia rsa/w and its
technology,development,people etc and that of the two stroke generaly.
For example I would also like to know more of the people involved,their way of thought the experiences
and suprises during development of the rsa/w on this thread and on another thead bother you with why
I keep burning hole through my piston....or what mr Thiel and yourself would have liked to try(eg24/7 , twin disk as mentioned before,etc)
Time is a matter...

PVO, I have just found a problem with the charging system I'm running. I'm using a small lead acid battery. I have never had a problem with the five lap VMX races I do, but have never been able to do a decent trail ride without the tuning changing half way through. For no apparent reason. Always thought it had somthing to do with running ethanol in an air cooled engine. I found the regulator rectifier had an open circuit when it got hot. Suddenly the battery would have to supply charge to run the system for sometimes up to ten miniutes, volts could drop as low as 9 volts, ( engine runs lean ) then the rectifier would cool and start working again. I sorted that issue this weekend, did a 30 K trail ride, tune stayed crisp. As a matter of interest, not fifty feet away from where we were parked ( at the trail ride ) was the CR500 EFI that has been featured in this forum ( Kiwi EFI CR 500 youtube video ). It now sports a carburator! It seems they could never get it to run right up to apporx 1/3 throttle no matter what they did. They injected into the throttle body. As I said earlier I had the same problem until injection timing was changed to just before transfer opened.
Some pictures of the throttle bodies I've cast up. I've machined one housing but have not made the throttle drum yet.


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XpTpSMTT a écrit:

Limit?of course not!!but to distinguish between two different things,the (his)story of the aprilia rsa/w and its
technology,development,people etc and that of the two stroke generaly.
For example I would also like to know more of the people involved,their way of thought the experiences
and suprises during development of the rsa/w on this thread and on another thead bother you with why
I keep burning hole through my piston....or what mr Thiel and yourself would have liked to try(eg24/7 , twin disk as mentioned before,etc)
Time is a matter...

XpTpSMTT a écrit:

+1 although,better late then never,it would be nice to start another thread on two stroke development so the masters and more
experienced on them can share their knowledge and keep this thread on the RSW/A 125 and the people behind it.

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2)

As it was i who asked the Question of Jan and Frits regading the Twin Disks. I asked it only because Jan himself had previously brought it up and i hoped he would expand on it. From What i understand Jan was involved in the RSA.................
I really sincerly apreciate the response recieved from all the people who contribute both questions and answers but especially the time devoted by both Jan and Frits

Frits Overmars a écrit:

Did you try the difference, Romeuh? Jan did....

I don't, but some bikes bring the exhaust like that a bit.

Would it be positive in reed valve engines if there were kinks outwards the flow after the carb, has the reeds make some return especially when rpm is out of the exhaust

uniflow a écrit:

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Very nice... but why the choice of a barrel type throttle rather than a conventional butterfly, or a slide with some sort of linear-to-rotary conversion (like on flat-slides for 4-strokes) for the tps? Isn't the longer body a disadvantage?

Jan:
"Jeff, the dimensions of the subports were very carefully determined.
Never removing more than 0,25mm at a time.
Making them as high as the main port costs a lot of midrange power.
And you have to keep them as far away from the transfer ports as possible.
So this is why they have a triangular shape."

Thank you very much for this response.