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

Howard Gifford a écrit:: Hi Frits. Is there a formula you use to calculate the target maximum rpm of a 2 stroke engine where it makes its best power? This would be helpful to design the pipe to this rpm.
It sounds like a simple question but undoubtedly the answer will be long.

Hi Howard. The bad news is that the answer is short: no; there is no simple formula.
You will need to calculate the time.areas for exhaust blowdown and scavenging, which is feasible with an appropriate computer program. But you will also have to take the flow coefficients of those ports into account which requires full three-dimensional flow calculations.
A simulation program like EngMod2T will do the two-dimensional time.area calculations (and a lot of other calculations, like pipe effects) quite well, but you will still need a dyno, a flow bench and a lot of experience to get to the RSA level.

Nombre de messages : 20 Localisation : Allemagne Date d'inscription : 22/05/2013

Hello two-stroke tuners all over the world .
At first I want to thank all of you - especially Jan and Frits -for creating these ~150 Pages of pure two-stroke knowledge. I learned more by reading these pages than by the reading of several books in the last two years :-)

Citation :: You will need to calculate the time.areas for exhaust blowdown and scavenging, which is feasible with an appropriate computer program. But you will also have to take the flow coefficients of those ports into account which requires full three-dimensional flow calculations.
A simulation program like EngMod2T will do the two-dimensional time.area calculations (and a lot of other calculations, like pipe effects) quite well, but you will still need a dyno, a flow bench and a lot of experience to get to the RSA level.

That is the point. A lot of Twostroketuners only look at the port in the liner.
A perfect example is this "ported" Malossi MHR Cylinder I got at the work desk and at the moment:
[Vous devez être inscrit et connecté pour voir cette image]
The Window in the liner has enough (probably to much) Timearea for everything. But the studs limit the time area a lot.

A question about connecting rods:
Does anyone know a source for a rod with 20mm bolt at the lower end and 16mm Pistonpin, with a lenght of more than 116mm?
Sadly I can not go bigger with my lower-end-bearing because my crank-housing diameter is allready at its maximum at the moment [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 998726

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 998726

Greatings from Germany
Tim Ey

Try: primatist srl in Italy.
That is where most Aprilia connecting rods were made.

Invité

Thanks for sharing your know-how and experiences here! [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 241515

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 241515

We learn a lot.

Nombre de messages : 12 Localisation : Germany Date d'inscription : 10/08/2012

Tim Ey a écrit:: A question about connecting rods:
Does anyone know a source for a rod with 20mm bolt at the lower end and 16mm Pistonpin, with a lenght of more than 116mm?

Samarin MT.211 ECM for Montesa Cota (see catalog on [Vous devez être inscrit et connecté pour voir ce lien] should have a length of 124 mm, 20 mm big end pin and 16 mm piston pin.

Edit: Sorry, I'm wrong. It has an 18 mm piston pin: [Vous devez être inscrit et connecté pour voir ce lien]

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Frits Overmars a écrit:: Like you suppose, the cylinder filling is deteriorating after 13000 rpm, Manuel.
In fact it is optimal at 12500 rpm where torque is at its maximum. The reason is that the time.areas (= the product of open port areas * the amount of time that these areas are open) becomes too small at high revs.
You can find a more thorough explanation as well as numerical and graphical values elsewhere in this topic.
Mechanical stress for piston and bearings has never been a problem.

Thanks Frits

Is always the rpm where the best torque is, the rpm where the best scavenging is?

Thanks Manuel

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Jan Thiel a écrit:: Try: primatist srl in Italy.
That is where most Aprilia connecting rods were made.

Hello

Jan were also the Crankshafts made at Primatist srl?

Thanks Mnauel

Jan Thiel a écrit:: Try: primatist srl in Italy.
That is where most Aprilia connecting rods were made.

I thought RSA connecting rods were made from french steel...

Manuel Rainer a écrit:: Is always the rpm where the best torque is, the rpm where the best scavenging is?

Scavenging is one of the main factors, but mixture strength, ignition timing and the surcharging provided by the exhaust pipe also play a role. The best torque is produced when the combination of these factors is optimal.
For example, at the rpm where the amount of cylinder filling is at its maximum, the ignition may be too early or too late, or the mixture may be too rich or too lean. Then the engine may produce more torque at an rpm where the ignition timing is better, or where the quantity of filling is a bit less but its quality is better.

Marc a écrit:

Jan Thiel a écrit:: Try: primatist srl in Italy.
That is where most Aprilia connecting rods were made.

I thought RSA connecting rods were made from french steel...

The first connecting rods from this French steel were made at Derbi.
They were unbelievably light.
Later they were also used in the RSA.
Who actually made them I do not know!

Thank you, Jan!

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 1993206895

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This topic still shows how pit-lane.biz is powerful! [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 771973

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked) - Page 14 771973

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

[quote="Manuel Rainer"]

Jan Thiel a écrit:: Try: primatist srl in Italy.
That is where most Aprilia connecting rods were made.

Hello

Thanks Frits

Jan were also the Crankshafts made at Primatist srl?

Thanks Manuel

Hi - in Part 1 of this thread there was a statement saying:

Citation :: Finally a simple advise for junior tuners: make the squish gap so tight that there is no more room for
mixture; if it is not there, it cannot detonate

Just wondering how far it is safe to follow that ? - another reference I remember was that 1% of stroke is a good number for squish gap - so with my 54mm stroke - 0.54mm gap...we have been using a head with 0.8mm gap - so could we safely go tighter ? 0.75 ? - 0.7 ? - and should we look at retarding the Ignition ?

For a 50mm stroke TZ, 0.7 was considered conservative, I usually aimed for about 0.6 to 0.65. I know someone who tried 0.55... but his bike blew up so often and for so many different reasons, I can't say whether he proved it one way or the other.

Thanks for the reply - I'm hoping to avoid any un-necessary blow-ups - if at all possible...
Another question about squish area - I've read about having the sharp edge between the squish & the combustion chamber - but cannot remember if there was any thoughts on the squish band angle - meaning - is it a good idea for the squish band to follow the piston dome radius ? - or should there be any sort of increase in gap towards the combustion chamber bowl ?
Thanks Very Happy

I tried a taper, thinking it might be useful to limit the ejection velocity... but the bike was slower.

Gordon Jones a écrit:: Thanks for the reply - I'm hoping to avoid any un-necessary blow-ups - if at all possible...
Another question about squish area - I've read about having the sharp edge between the squish & the combustion chamber - but cannot remember if there was any thoughts on the squish band angle - meaning - is it a good idea for the squish band to follow the piston dome radius ? - or should there be any sort of increase in gap towards the combustion chamber bowl ?
Thanks

The squish band should follow the piston radius.
That was our conclusion after many tests!

Jan Thiel a écrit:: The squish band should follow the piston radius.
That was our conclusion after many tests!

Thanks very much Jan - very glad to hear that ! - I spent time making a tool to cut the squish band - with the facility to adjust the radius - it uses a small rotary table to hold the tool tip.
We have been trying some tighter squish clearances recently on a TZ350 engine - using 0.8mm at the last race meeting & running very well - just fitted new pistons & the gap is slightly different at .075 / 0.77 - just deciding if it's enough of a difference to cause any detonation problems... scratch

Hi Jan,
On the RSA125, was the radius on the cylinder head bowl design to direct the mixture turbulence in a particular direction or was it just a means to achieve the volume with the required squish surface ratio?

Also, what unlead fuel did you test with?

Thank you for your answer,
Allan.

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

hi

Jan has always been the dellorto 42mm carb driven on the RSA or have you also had the VHSB 39?

how big is the performance increase between the two carburetors?

thanks Manuel

Manuel Rainer a écrit:: hi

Jan has always been the dellorto 42mm carb driven on the RSA or have you also had the VHSB 39?

how big is the performance increase between the two carburetors?

thanks Manuel

We started by using the same carburetor as the Aprilia RSW.
Later Dell?Orto made a special carburetor for the RSA.
There were a lot of problems due to the inclination!

GtG001 a écrit:: Hi Jan,
On the RSA125, was the radius on the cylinder head bowl design to direct the mixture turbulence in a particular direction or was it just a means to achieve the volume with the required squish surface ratio?

Also, what unlead fuel did you test with?

Thank you for your answer,
Allan.

It was just meant to achieve the required volume.

We tested all makes of racing fuel.
There was nearly no difference between them!

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Jan Thiel a écrit:

Manuel Rainer a écrit:: hi

Jan has always been the dellorto 42mm carb driven on the RSA or have you also had the VHSB 39?

how big is the performance increase between the two carburetors?

thanks Manuel

We started by using the same carburetor as the Aprilia RSW.
Later Dell?Orto made a special carburetor for the RSA.
There were a lot of problems due to the inclination!

thanks Jan

which carburator was used in the RSW?

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» [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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