[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 Frits Overmars le Lun 19 Nov 2012 - 16:48, édité 1 fois

Quite right, Vagelis.
In my FOS scavenging system I use 192°/130° timing, giving 31° blowdown angle. Yet the angle.areas will allow the 125 cc version to produce its maximum power at 16,500 rpm.
Now where do I find a big end bearing that will play along? scratch

Yes ; the CVT is great for high strung small displacement race powerbands ... I agree that 138 deg. is lots of transfer timing and we will reduce it some seeing as how we are now widening them more to prevent seizure . That timing is for the C ports , our a and b ports are a bit less.. I can see that it will still be an empirical task to improve on what we have..... Your advice and experience has sped this process up and for that we are grateful... thankyou ... 2013 - [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 23 980796

2013 - [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 23 980796

Dernière édition par Frits Overmars le Lun 19 Nov 2012 - 17:06, édité 1 fois

You're welcome Mike. It will indeed still be an empirical task, as the angle.areas are only part of the story.
You can have two ports with identical timing and angle.areas, and one may flow 20% better than the other....

Ideally we should not use the angle.area concept; instead we should use angle.flowrate. Computational Fluid Dynamics should be able to do that if you can persuade CFD to get all the pressure fluctuations right.
At the moment CFD for two-stroke development mainly means: garbage in > garbage out silent

.

Frits Overmars a écrit:: A single port cannot open the same amount of area per crankshaft degree as a double or triple port because its shape is limited by piston ring life. So yes, the difference can be significant. That is rather empirical; lower transfers limit the rpm at which the cylinder can still be adequately scavenged; higher transfers limit the exhaust blowdown angle.area. In my FOS scavenging concept (picture below) there is so much blowdown angle.area available that the transfers could have been higher than 130°, but I stuck with these 130° because higher transfers will narrow the powerband; exhaust pulses returning too early would have more opportunity to push the fresh charge back from the cylinder into the crankcase.

Thank you Frits for your answer. I understand everything.

Changing the topic a little bit...

1.) In case of a piston controlled inlet port is it right, that the suggested opening angle is 160 degrees which value is independent from the rmp? Is this true even if the time area or the angle area are too small?

2.) If I'd like to get the time or angle area I should count it from the size of the carburator's area, shouldn't I? If the area of the inlet port is bigger than the area of the carburator will I get appropriate values for the time and angle area, or not?

Forgi a écrit:: In case of a piston controlled inlet port is it right, that the suggested opening angle is 160 degrees which value is independent from the rmp? Is this true even if the time area or the angle area are too small?

No, the inlet event is completely different. Here you should try an inlet tract as short as possible, a large carburator and the shortest timing that will produce sufficient power.
Any inlet tract is much too short for pulse resonance; between Inlet Open and Inlet Close a pulse would cover as much as five times the tract length and it would have hardly any energy left by the time the inlet closes. For the inlet system the Helmholtz resonance is all-important.

Citation :: If I'd like to get the time or angle area I should count it from the size of the carburator's area, shouldn't I? If the area of the inlet port is bigger than the area of the carburator will I get appropriate values for the time and angle area, or not?

If you calculate the angle.area of the carburator you will get huge values because it is always open. Calculating angle.areas only makes sense if you do it at the port.

Frits Overmars a écrit:: You're welcome Mike. It will indeed still be an empirical task, as the angle.areas are only part of the story.
You can have two ports with identical timing and angle.areas, and one may flow 20% better than the other....

Ideally we should not use the angle.area concept; instead we should use angle.flowrate. Computational Fluid Dynamics should be able to do that if you can persuade CFD to get all the pressure fluctuations right.
At the moment CFD for two-stroke development mainly means: garbage in > garbage out .

Thats why we love our dyno .....It sorts things out .... 2013 - [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 23 980796

Frits Overmars a écrit:

Forgi a écrit:: In case of a piston controlled inlet port is it right, that the suggested opening angle is 160 degrees which value is independent from the rmp? Is this true even if the time area or the angle area are too small?

No, the inlet event is completely different. Here you should try an inlet tract as short as possible, a large carburator and the shortest timing that will produce sufficient power.
Any inlet tract is much too short for pulse resonance; between Inlet Open and Inlet Close a pulse would cover as much as five times the tract length and it would have hardly any energy left by the time the inlet closes. For the inlet system the Helmholtz resonance is all-important.

Citation :: If I'd like to get the time or angle area I should count it from the size of the carburator's area, shouldn't I? If the area of the inlet port is bigger than the area of the carburator will I get appropriate values for the time and angle area, or not?

If you calculate the angle.area of the carburator you will get huge values because it is always open. Calculating angle.areas only makes sense if you do it at the port.

Well, I'm affraid I wasn't clear enough. I mean what if the size of a carburetor is limited for example because of a rule of competition...? In this case we only have a given small sized carburetor so if we'd like to get a convenient time area, we have to make a significant increase of the inlet port's angle.

Concerning the second question I tried to say that we calculate the time area applying the value of the inlet port's angle and the value of the carburetor's area. So the inlet port which is bigger than the size of the carburetor is unnecessary and if we take into account such area it will lead us to a wrong result, or we can easily mislead ourselves.

Drawins are also attached.

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I have a question, maybe a bit offtopic.

A nearby company makes coatings, titanium coatings, one worker from there said to me that the surface of the cylinder I showed him would cost around 130€ to coat with 0.03 mm thick titanium.

Why not titanium coating instead of nikasil?
It would be possible to make the honing with soo thin thikness?

I don't know exactly what temperature they need to heat the surface wall of the cylinder...
I don't know if the ring material would have to be changed...

Or the titanium would eat the piston??? lol!

Regards

Nombre de messages : 41 Localisation : Italia Date d'inscription : 20/11/2012

Jan Thiel a écrit:

ridley a écrit:: "At Aprilia we had a very good epoxy, called 'stucco verde' in Italian.
Never worked loose and even withstood replating!
Sorry I do not know were it was made!"

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Yes, that's it!

Hi Jan, which one, exactly?
Thanks a lot to share with us your huge knowledge!

The one above Filandro!

Thanks for that Jan.

This place can expect to be swamped with orders 2013 - [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 23 809262

2013 - [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 23 809262

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Nombre de messages : 41 Localisation : Italia Date d'inscription : 20/11/2012

Thanks a lot, ordered just now.

Nombre de messages : 28 Localisation : Slovenia Date d'inscription : 19/03/2012

I would like to ask a question; what kind of gaskets is best to use between the cylinder and carter, metal or "paper" type?
Could a "paper"-type gasket help transfer less heat to the carters and thus have less heat transferred to the fresh intake charge?
I noticed competition kart engines use paper-type gaskets.

Thanks for your answer.

Paper gaskets are fairly good heat insulators, compared to metal gaskets. Their drawback is that they set during use. That is why Honda used no gaskets at all on their two-stroke works racers; instead they fitted O-rings between cylinders and crankcase.
Of course, when cylinders and crankcase are both well cooled, there is hardly a temperature difference and in that case the insulating property of a gasket becomes unimportant.

Sujet: Auxiliary exhaust ports Jeu 29 Nov 2012 - 2:14

Hi Jan,
Was there much HP gain from extending the auxiliary exhaust ports below the front of transfer port A? – (the side closest to the main exhaust)

Thanks for your answer in advance.
Regards
Allan.

GtG001 a écrit:: Hi Jan,
Was there much HP gain from extending the auxiliary exhaust ports below the front of transfer port A? – (the side closest to the main exhaust)

Thanks for your answer in advance.
Regards
Allan.

I think that was already explained in the first pages.

What I did not find in my search was the C port Open angle?

What changes are made by the angle of C port?

Do we really lost charge at high rpm by directing it towards the exhaust?

Thanks

Nombre de messages : 30 Localisation : Greece Date d'inscription : 09/07/2011

I 'm not sure of the aux-ex full-open point, probably just below 115°, judging from this [Vous devez être inscrit et connecté pour voir ce lien]
But if you look at the earlier ap- cylinders, auxiliaries were closer to the front TFR than in the latest cylinders. And of course, Jan said that, in general, they should be as far as possible, to prevent direct fresh charge loss at tfr opening.

C port opens at 114°, same as B ports. Axial angle of the older APC (I think) cylinder was 52.3°. I guess this hasn't changed much, given the role of the port.

And... I couldn't help you about the 2nd and 3rd question 2013 - [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 23 858879

2013 - [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 23 858879

Nombre de messages : 28 Localisation : Slovenia Date d'inscription : 19/03/2012

Frits Overmars a écrit:: Paper gaskets are fairly good heat insulators, compared to metal gaskets. Their drawback is that they set during use. That is why Honda used no gaskets at all on their two-stroke works racers; instead they fitted O-rings between cylinders and crankcase.
Of course, when cylinders and crankcase are both well cooled, there is hardly a temperature difference and in that case the insulating property of a gasket becomes unimportant.

Thanks for your answer mr. Overmars!
I think I'm going to try it out. Perhaps also I'll try an insulation coat for the crankcase insides, our CVT produce quite a lot of heat that also dissipates on the engine block. And the cooling system is hard to improve.

GtG001 a écrit:: Hi Jan,
Was there much HP gain from extending the auxiliary exhaust ports below the front of transfer port A? – (the side closest to the main exhaust)

Thanks for your answer in advance.
Regards
Allan.

This area
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For everybody here tuning cylinders, what was the result of this?

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I did it twice, I notice the spark a bit leaner, I ajust but not sure if improved something, I don't have a dyno.

Dernière édition par eric² le Ven 30 Nov 2012 - 23:19, édité 2 fois

All edge is a plague in an two stroke engine.

The edge in photo engenders a loss of filling, you can correct it with the Frits method.

For many detail it is simply necessary to be logical.

I didn't understand what you mean

sorry, i cannot explain more simply... use your logic !

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

i think he was trying to say that every sharp edge in a 2 stroke engine is not good and with logical thinking you'll know why...

koenich a écrit:: i think he was trying to say that every sharp edge in a 2 stroke engine is not good and with logical thinking you'll know why...

I just asking for everyone "experience" on changing that, more overrev? More peak? More botton end? More overall power? Logic is not always working 100%

.... not every sharp edge is bad, like the squirt of the piston, the squish/chamber edge, etc are better keeping sharp...
:)

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