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

Nombre de messages : 5 Localisation : Uruguay Date d'inscription : 30/04/2012

Thanks Jan and Frits for share your knowledge on racing two strokes engines. I have a question for you:¿how important its the sheet metal thickness on a pipe performance?

Normally 1mm thickness is used.
Less will crack and more is unnessessary.

Nombre de messages : 37 Localisation : Hellas Date d'inscription : 08/02/2012

Is there a possibility someone more...computer inclined
save this entire thread including part1 and upload somewhere?admin?

Nothing is impossible but... I think that the host company put a kind of "anti hacking" system that don't allow to record more than 5 pages at once.
Or something like this.

Anyway, it would be a good idea and i will try, but it will take time.

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 980796

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 980796

Jan Thiel a écrit:: Normally 1mm thickness is used.
Less will crack and more is unnessessary.

I normaly fabricate from 0.75mm, they crack if they are mounted to tight ! I have up scaled as many features of the Aprilia cylinder into a 78mm bore, that seems to have more linear power and better piston cooling.

I manufacture hydroformed pipes and I agree with Jan that 1mm or 19 gage cold rolled steel works best. Going thinner especially on bigger engines that tend to vibrate more will result in a shorter life span for pipes and they will crack. Going to thicker metal adds weight but does make the pipe more durable. Thicker pipes need more warm-up time to stabilize the temperature and come up to full revs. Thin pipes do tend to heat up an cool faster which is good for a drag racer but not for a track engine.

Thanks for reminding me I'll have to go and tell 40-50 people their big bore vintage mxer pipe I made for them 7-8years ago is about to fracture at any moment Rolling Eyes

Most circuit racing is a crazy drag to the first turn and short series of drags between turns for each lap there after.

Back to the topic ...............Jan I often wonder what the output of 2012/3 RSA would be if you were still inclinded to work for Aprilia and develop the engine also would solving the part throttle deto problems or the top end power be the main priority.
Were you ever presented with 'wish lists' from riders, this rider wants more bottom end, that one wants more top end, more linear power etc etc or was it just everyone wanted more and was happy (sort of) when they got it?

IoTS you seem to be a bit of a sarcastic sob but I will ignore that for now. [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 438659

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 438659

Obviously you seem to have had success with thin wall pipes so good for you! Your pipes seem to be imune from vibration fatigue but I have been around long enought to see a pipe failure or two as well. Thin pipes (under .035") tend to have shorter life spans. Most of the failures I have seen were due to vibration. Cracks appear within inches of the cylinder or where the tail pipe welds on. Also the weld-on fittings for temperature sensors seem to be a source for cracks to develop on thin wall pipes. Going to .040 or thicker reduces the likelyhood of pipe failures. if you argue that fact then I cant help you..
But as you said, lets get back to the topic. A question for Frits about the RSA pipe. I know the race pipes were titanium and were well crafted. Who was the craftsman that made those pipes? [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 101130

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 101130

Those titanium pipes were made by Sam Balder of the Samba company in Alkmaar, Netherlands.

Top quality job and top quality news!

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 771973

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 771973

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 199739

Very impressive.
Here is the link to their web site
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Nombre de messages : 30 Localisation : Greece Date d'inscription : 09/07/2011

Here's a shop with lots of Samba pipes: [Vous devez être inscrit et connecté pour voir ce lien]
Looking around at honda pipes, there are different models, stated "work only with xy".

Frits, might you know what it means when a pipe is "Non-powervalve" operational (or the opposite)? I assuse the "deto-resistive" has to do with the stinger diameter after the nozzle, right?
Furthermore, do you or Jan remember the dimensions of the silencers you used? There were major changes between fuels types and tracks?

---

On peut trouver beaucoup des Samba pots a l' e-shop ici : [Vous devez être inscrit et connecté pour voir ce lien]
En observant les Honda pots, il y a des modeles differents, cites "fonctionne seleument avec .."

Frits, pourrais-tu nous expliquer qu'est-ce que ca vais dire, quand l' echappement est "Non-powervalve" operative (ou le contraire)? J' imagine que le "deto-resistive" est connecte avec la diametre du stinger, apres la nozzle-restriction.
(excuse my french, I can't keep up any more, as I thought :/)

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

Howard Gifford a écrit:: Your pipes seem to be imune from vibration fatigue but I have been around long enought to see a pipe failure or two as well. Thin pipes (under .035") tend to have shorter life spans. Most of the failures I have seen were due to vibration. Cracks appear within inches of the cylinder or where the tail pipe welds on. Also the weld-on fittings for temperature sensors seem to be a source for cracks to develop on thin wall pipes. Going to .040 or thicker reduces the likelyhood of pipe failures. if you argue that fact then I cant help you..

lifetime fatigue depends on the vibrations but is also influenced by the applied heat and heat expansion Howard. Those factors lead to bending forces and seen over the lifetime its described by the bending fatigue strength. Wöhler curve shows pretty good how can get a long lasting pipe:

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Vagelis a écrit:: Here's a shop with lots of Samba pipes: [Vous devez être inscrit et connecté pour voir ce lien]
Frits, might you know what it means when a pipe is "Non-powervalve" operational (or the opposite)? I assuse the "deto-resistive" has to do with the stinger diameter after the nozzle, right?
Furthermore, do you or Jan remember the dimensions of the silencers you used? There were major changes between fuels types and tracks?

I am not going to comment on statements that other people use in their advertisements; you will have to ask them directly.
At the moment I have no access to silencer dimensions. Maybe Jan does.
Fuels evolved rather gradually. There were no adaptions to different tracks.

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

Hi Jan & Frits
Would you share you knowledge with regards to compression ratios and weather conditions with the RSA, did you alter this much, would you show us some examples of these changes [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 771973

We always used a 16:1 ratio on the dyno.
What they used on track I do not know.
What happened on track was never communicated......

RAW a écrit:: Hi Jan & Frits, Would you share you knowledge with regards to compression ratios and weather conditions with the RSA, did you alter this much...

We would love to alter the weather conditions, RAW, but we haven't yet worked out how to do that.
There seems to exist a dance for it....

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

Thanks Jan, very funny Frits, clearly I will have to be very carefull how I approach you with my queries, how on earth did you find the time to experiment with 2strokes given your daily comedian profession.
All jokes aside though would you share your opinion upon the tuning of a 2stroke with the changing altitude conditions, namely with compression ratios. Is there a simple set of rules to work with ?

The simple rule would be that an engine will tolerate a higher compression ratio in a lower air pressure. But that lower air pressure would cause less power, hence a lower exhaust gas temperature and a lower resonance rpm. And raising the compression ratio woud aggravate that rpm loss.
What you can do, is compensate a lower air pressure with a narrower tailpipe restrictor. That will restore part of the rev loss. But I would not tell this to any race mechanic. In my opinion the risk of him overdoing it would not outweigh the advantages.

Ah Frits you are smart. Race track tuning usually involves the philosiphy that if a little is good then a lot must be better. I have started a shelf for burnt pistons, offerings to the gods of speed from poor choices at the track. Pretty soon I will need a bigger shelf!

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

Thanks Frits, that's very interesting
I was once told by a racer that with the inline engines they have different size main jets in the carburetors, several years later I spoke again with this same racer and he had informed me that the main jet sizes are the same now and that the diameter of the tailpipe restrictor is smaller on the rear cylinder.
In your experience is there some truth to this ?
I imagined this may be a result of pipe routing / pipe shape inconsistencies between the 2 cylinders
Would you please enlighten us all more so with pipe function and design [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 9 980796

Howard Gifford a écrit:: Ah Frits you are smart. Race track tuning usually involves the philosiphy that if a little is good then a lot must be better. I have started a shelf for burnt pistons, offerings to the gods of speed from poor choices at the track. Pretty soon I will need a bigger shelf!

Howard,

At Aprilia we had some problems with piston burning.
We changed the head design, bringing the cooling water as close as possible to the sparkplug.
After that we never had problems any more!

Jan did you find the torroidial design worked better than the hemispherical design in the RSA?
I have always found the hemispherical design works best but my budget does not allow me to make more than a couple of designs to test at a time. What would you recommend to concentrate my efforts on? Toroidial, hemispherical or the bathtub design?
Also a while back (1985)it was popular to see an offset combustion chamber usually towards the intake side of the piston. Did you ever try this and if so was there any gain?

I'd just like to thank everyone involved here for an awesome resource. I've been watching this thread for months now and it's an amazing compilation of information. Thank You! I just wish there was something I could add so I didn't feel like such a leech, but I'm just a hacker home tuner lol.

Howard Gifford a écrit:: Jan did you find the torroidial design worked better than the hemispherical design in the RSA?
I have always found the hemispherical design works best but my budget does not allow me to make more than a couple of designs to test at a time. What would you recommend to concentrate my efforts on? Toroidial, hemispherical or the bathtub design?
Also a while back (1985)it was popular to see an offset combustion chamber usually towards the intake side of the piston. Did you ever try this and if so was there any gain?

The best head design at Aprilia was hemispherical, with a wide squish band and parallel squish angle.
So that would be my advice.

I used an offset combustion chamber on the Garelli's.
When I tried to turn the head 180° there was no difference!
We even won the 1986 world championship with the heads in this position! Just for fun.
For 1987 I turned them back again to the 'normal' position.

» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)
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