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

Dernière édition par Jan Thiel le Jeu 27 Sep 2012 - 7:08, édité 5 fois

Howard Gifford a écrit:: This question is for Frits and Jan. The RSA engine looks to have a superior porting design and layout as cast but as with most engines there is the insatiable need to get in with a grinder to clean things up and do any port matching. My question is,,,how many hours were spent "race prepping" a cylinder before it was deemed raceable? Also was there one cylinder that stood out as superior to all the others and was impossible to duplicate the power output on the dyno? Who was the main man with the grinder?

The most time was spent narrowing the bridges in the exhaust duct.
These could not be CNC machined:the inside was unreachable.
Preparing for plating took about half a day.
And preparing for dyno testing another half day.
A cylinder 'untouched' after plating would give 1,0 to 1,5 Hp less.
All cylinders destined for 'works' riders were dyno tested.
And reworked in case of missing HP.
We could dyno at maximum 3-4 cylinders a day.
Difference between 'best' and 'worst' cylinders was about 0,4 HP.
There were 2 people grinding cylinders daily.
I only did necessary corrections personally.
There were 2 dyno's working every day.
About 300 cylinders were made every year.
And apart of this we also constantly tried to improve HP.
Mostly batches of 30 cylinders were cast, 25 'as before' and 5 with small changes.
Between casting and dynoing took about 3 month's time.
We also dynoed replated cylinders.
They were almost never as good as new one's!

mxer a écrit:: This question is for Frits or Jan.

I remember Jan said the lower part of the C port is almost always lower than the B and A
ports in most engines. I always thought this was done to stop ring snag on the way down.
I have a hard time making out Aprillas bottom of C port. Did you v the bottom of C port to
put ring back in groove?

First the bottom of the C-port was lower than the pistonring at BDC.
Then the C-port was made narrower, to be able to make the B-ports wider.
The idea was that the near horizontal B-ports would flow more than the steeply upward angled C-port.
This gave a good improvement, and was done in 1997.
Later the bottom of the C-port was raised until nearly BDC
We made 4 cylinders, just to try.
They gave better power and caused no problems at all.
This was done in 1999, halfway through the season.
After that all cylinders were made like this.
The bottom of the C-port is not quite as important as the bottom of the A and B-ports.
Because of its upward direction it does not cool the piston much!
A still narrower C-port was tried, (12mm) but this lost some power.
Also a cylinder without C-port, and still wider, bridged, B-ports was tried, with negative result.

Jan, thank you for your words of wisdom. This type of information is what we all are here for. I am sure everyone on here listens to your every word and will incorporate your advice in their projects. I personally have made major gains using what I have learned about port design reading these pages.
I will be in your country this March at a wedding and I would love to meet you in person.
Again ,,,many thanks.
Howard...

After plating was there much prepping or were the cylinders chamferred at the plating shop? Did you find the amount of chamfer affected the performance much?

Howard Gifford a écrit:: Jan, thank you for your words of wisdom. This type of information is what we all are here for. I am sure everyone on here listens to your every word and will incorporate your advice in their projects. I personally have made major gains using what I have learned about port design reading these pages.
I will be in your country this March at a wedding and I would love to meet you in person.
Again ,,,many thanks.
Howard...

It would be nice to meet, I live near Bangkok.
So you're welcome.

Chamfers at the transfers gave less power.
A radius at the exhaust was better.
But this also depends on your exhaust pipe.
Many years ago we used unchamfered exhaust ports on the 50 and 125/2 engines.
And kept the exhaust port as low as possible.
I discovered this did not work on a 125 Aprilia cylinder.
Maybe because the exhaust pipe was already made for a high exhaust port!
A radiused exhaust port flows better, but I think a sharp edge may give a stronger pressure wave.
You only arrive at the best compromise by testing.

You should always prepare your cylinders yourself before plating.
NEVER permit the plating shop to do this!
Because they have NO idea about the importance of chamfers etc.
Once Gilardoni destroyed my best 50cc cylinder this way!
30 years ago, I still get angry when I think about it!

Jan Thiel a écrit:: You should always prepare your cylinders yourself before and after plating.
NEVER permit the plating shop to do this!

Yes, of course Frits!
I really did not think anybody would be stupid enough to do this!
But you never know....

Remember Albert Einstein's words:
"Only two things are infinite: the universe and human stupidity. And I'm not yet sure about the universe...."

Albert Einstein also said'
“We can't solve problems by using the same kind of thinking we used when we created them.”

“Any fool can make things bigger, more complex, and more violent. It takes a touch of genius-and a lot of courage-to move in the opposite direction.”

Howard Gifford a écrit:: Albert Einstein also said “We can't solve problems by using the same kind of thinking we used when we created them. Any fool can make things bigger, more complex, and more violent. It takes a touch of genius-and a lot of courage-to move in the opposite direction.”

A simple design is not something you will achieve through sloppy thinking; on the contrary. I tell my pupils: "When you think you have finished a design, think a bit more and try to eliminate as many parts as possible. Each part that you can leave out, doesn't cost anything, doesn't weigh anything and never breaks down.

Nombre de messages : 2 Localisation : Sweden Date d'inscription : 25/09/2012

Frits Overmars a écrit:

Blommen a écrit:: HI, are you able to send me that Cad file?

Hey Dennis, I think you just proved that the Swedish have a great sense of humour [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 12 809516

[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 12 809516

.

I guess couldn´t agree more [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 12 921866

[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 12 921866

I was expecting that kind of answer, but i figured it was worth a try. With some luck i could have been a "public" sketch that houndreds of people had but i hade missed it troughout the thread.

I find it very useful that you and Jan ar able two answer our questions about 2-stroke tuning and on such famous engine.

No need for a presentation on me, im just a happy amatuer and im only 17 yrs old. Very Happy

Frits Overmars a écrit:

Blommen a écrit:: HI, are you able to send me that Cad file?

Hey Dennis, I think you just proved that the Swedish have a great sense of humour [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 12 809516

.

[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 12 998726

[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 12 2878

[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 12 980796

Frits Overmars a écrit:: "When you think you have finished a design, think a bit more and try to eliminate as many parts as possible. Each part that you can leave out, doesn't cost anything, doesn't weigh anything and never breaks down.

Lean thinking [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 12 771973

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

What can be done after the plating without damaging it?
Is there a compromise between chamfering the transfer ports and longevity of the rings?

Is it possible to reveal the ignition timing of the RSA?

Nombre de messages : 6 Localisation : usa Date d'inscription : 14/09/2012

XpTpSMTT a écrit:: What can be done after the plating without damaging it?
Is there a compromise between chamfering the transfer ports and longevity of the rings?

Is it possible to reveal the ignition timing of the RSA?

A lot can be done. I have used 3 plating companys and get 3 different results. All require more touch up work.

Thanks for the transfer port clarification Jan.
I am with Howard. I already made some gains from this great thread.

XpTpSMTT a écrit:: What can be done after the plating without damaging it?
Is there a compromise between chamfering the transfer ports and longevity of the rings?

Is it possible to reveal the ignition timing of the RSA?

The best way to work on plated cylinders is by using dental diamond burs.
There were never any problems with the piston rings with unchamfered transfer ports.

Frits should have the ignition curve of the Aprila RSA.
No problem to show it I think.

Jan Thiel a écrit:: The best way to work on plated cylinders is by using dental diamond burs.
There were never any problems with the piston rings with unchamfered transfer ports.

Clear and very usefull!

[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 12 1993206895

[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 12 1993206895

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

mxer a écrit:: ......touch up work.

ok,i thought maybe there was more i was missing.

But why do most production cylinders(at least the ones i have seen)
have some sort of chamfering,some more others less?
So my problems are coming from somewhere else and unchamfered ports were not the cause.
Does this also aplly for cast iron cylinders or iron sleeved?

The only way to break a piston ring at Aprilia was through insufficient ring gap clearance.
It had to be 0,30, less would cause the ends to touch!
Then the ring would become very hot, expand even more, and the only place to go was into the exhaust port.
Result: a broken ring and a ruined cylinder.
0,25 clearance was insufficient!

About the chamfers, of course it makes no difference if the cylinder is plated, cast iron, or has a liner.
But you must have good quality piston rings!

Sujet: Port finishing Lun 1 Oct 2012 - 10:40

Hi Jan,
Thank you for the comments about port chamfers - could you describe how you finish the cylinder ports after the cylinder is plated please? [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 12 809262

[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 12 809262

Best regards
Allan.

Jan Thiel a écrit:

XpTpSMTT a écrit:: Is it possible to reveal the ignition timing of the RSA?

Frits should have the ignition curve of the Aprila RSA. No problem to show it I think.

No problem at all, Jan, especially beause I already posted it once in Pit-Lane Wink

. I cannot find where that was (I can never find anything with the search funtions of forums), so here it is once more.
[Vous devez être inscrit et connecté pour voir cette image]

Dank u Frits...
If I could then ask 2 supplementary questions:
- was the curve modified at partial throttle to try to reduce detonation?
- did the timing evolve at all with different versions of Elf mits-xx ?

GrahamB a écrit:: ...was the curve modified at partial throttle to try to reduce detonation?

The part-throttle detonation was caused by the scavenging pressure dropping soo low that burnt gases entered the transfer ducts, notwithstanding a blowdown time.area that was sufficient for full throttle at high revs. It was not a situation that could have been cured by altering the ignition timing.

Citation :: did the timing evolve at all with different versions of Elf mits-xx ?

Aprilia did not use Elf products....

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

yes,I have found the importance of ring gap the hard (and expensive)way!
But still 0,3mm seems large
(???),does it have to do with the breaking in of the new piston and cylinder
or lack of?How was it done(braking in)
What should the correct gap be then for 67mm bore?steel rings.

Thank you for the advance curve,it says 100% throtlle
Was it corrected from the TPS reading or other factors?

(edit:eg for smooth acceleration inside corners)

Nombre de messages : 19 Localisation : England Date d'inscription : 07/09/2012

I've pulled this from Part 1

Jan Thiel a écrit:: Very little computer simulation was used, as far as I remember only for the cilinder and head cooling.
We once had an exhaust design software on loan from a very well known company, the results were useless! It was mostly cut and try!
Cilinder development was done without any computing, just logical thinking.
The exhaust ducts were CNC machined.
All improvements were fully understood..

Could you divulge the name of the exhaust design software?

» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)
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