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

Nombre de messages : 15 Localisation : Germany Date d'inscription : 06/05/2012

Hell wax, how did you do this tests?
You made distance discs in relation to the lead of the spark plug thread? And made the dyno test with one spark?

Or did you search spark plugs with different thread startings in relation to the electrode?

I'm just asking because method 1 changes the compression ration. Not a lot, but maybe enough to disturb the result.

Daniel A. a écrit:: Here is the promised photo. Nice to see the difference between static ignition and variable ignition :)

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The stutter is not a problem anymore. It's still there but you can live with it. Thanks for all the hints!

I will try to remove the wave at ~10500 with different exhaust dimensions now.

Frits, what do you think, is my current exhaust too short or is it okay? Ignition at max torque (12200rpm) is 25° before tdc. Considering that you once told, ignition advance at max torque should be around 14° I would conclude, that my exhaust is actually too short.

Regards,
Daniel

If you could please post a video how is that simson running :)

questions for you Frits and Jan

You said earlier in this topic that a racing 2 stroke engine must have basically an exhaust at 190° and transfert at 130°
do these values are also available for a MX 125 engine or must be lower?

About transfert ports on RSA cylinder it seem the ports B and C are a bit higher than Part A (near 0.6mm) i noticed that on many other cyliders it's the opposite port A spite first then B and C and sometime C after B Can you explain why this difference and what advantages to make "spiting transfert in this order on RAS?
Thanks for your answer

Pierre

Daniel A. a écrit:: Frits, what do you think, is my current exhaust too short or is it okay? Ignition at max torque (12200rpm) is 25° before tdc. Considering that you once told, ignition advance at max torque should be around 14° I would conclude, that my exhaust is actually too short.

Your power curve looks very good, Daniel. I am amazed that an engine making that much power would survive an ignition timing of 25° bTDC at max.torque rpm. Are you certain that this timing is correct? If yes, then the exhaust could be too short, but remember that I know virtually nothing about your engine, so I can only guess.

pierre95 a écrit:: questions for you Frits and Jan
You said earlier in this topic that a racing 2 stroke engine must have basically an exhaust at 190° and transfert at 130°. do these values are also available for a MX 125 engine or must be lower?

These 190°/130° values are valid for every kind of competition two-stroke engine.

Citation :: About transfert ports on RSA cylinder it seem the ports B and C are a bit higher than Part A (near 0.6mm) i noticed that on many other cyliders it's the opposite port A spite first then B and C and sometime C after B Can you explain why this difference?

No, you would have to ask the makers of those other engines why they did what they did.

Citation :: what advantages to make "spiting transfert in this order on RAS?

I do not understand this question, Pierre.

I have a question for Jan. In your dyno testing the RSA (or any other engine) did you find that the engine seems to perform better at a higher rpm at the track than on the dyno? Our testing shows that our engines pull well beyond the point where they start to lose torque on ther dyno. Our best performance is around 10400 rpm but onb the dyno it peaks at 10,000. Our dyno is an eddy current Schenck W70 hooked to a Land and sea data aquisition system, I pump 3000 cfm fresh air into the dyno room. The ehhaust is vented outside well away from the intake air.
Could this be an air quality issue? It is not a tach problem as I have verified the data aquisition (mychron 3) against both tachs on the dyno. We also have to run 2-3 sizes richer at the track to get proper piston wash.
The engine is a 440 cc 180 degree twin cylindeer 65 mm bore 65.8 mm stroke.

Nombre de messages : 60 Localisation : australia Date d'inscription : 01/06/2012

el castor a écrit:: Hell wax, how did you do this tests?
You made distance discs in relation to the lead of the spark plug thread? And made the dyno test with one spark?

Or did you search spark plugs with different thread startings in relation to the electrode?

I'm just asking because method 1 changes the compression ration. Not a lot, but maybe enough to disturb the result.

Buy a box of spark plugs, mark them all until you get ones that line up. Thsi was on a jetski so I was just using a rev counter to see what was happening up top. It would pull a clear 150rpm more on a lined up set of plugs. You need more power to pull the prop higher on a jetski. I then put in a set of plugs that were wrong and got a 150 rpm drop. On a jetski this is worth just over 1mph when your drag racing up to the first turn then its worth having

pierre95 a écrit:: questions for you Frits and Jan

You said earlier in this topic that a racing 2 stroke engine must have basically an exhaust at 190° and transfert at 130°
do these values are also available for a MX 125 engine or must be lower?

About transfert ports on RSA cylinder it seem the ports B and C are a bit higher than Part A (near 0.6mm) i noticed that on many other cyliders it's the opposite port A spite first then B and C and sometime C after B Can you explain why this difference and what advantages to make "spiting transfert in this order on RAS?
Thanks for your answer

Pierre

Pierre,

I think this depends on the type of exhaust port used.
Our exhaust port had auxiliary ports.
You make these as big as possible to gain blowdown, and power.
As big as possible means you make them bigger in all directions until power drops!
With small, mostly 0,25mm at a time, modifications.
You then arrive quite near to the transfer A-port.
Keeping this a bit (0,5mm) lower proved to be better.
And then making the B-ports higher improves power.
By raising the A-port even 0,1mm we immediately lost power.

Nombre de messages : 22 Localisation : Perth, WA Date d'inscription : 28/12/2012

Frits & Jan,

Just wondering if you ever pursued a desaxe offset in any of your engines and if there was any benefit?

Thanks

Ken

Ken Seeber a écrit:: Frits & Jan,

Just wondering if you ever pursued a desaxe offset in any of your engines and if there was any benefit?

Thanks

Ken

I always had the pistonpin offset towards the exhaust port.
Once I did try the difference when I worked at Bultaco.
Offset towards the exhaust port was the best.
Offset to the other side a little bit worse.
And the worst was no offset.

Nombre de messages : 55 Localisation : Germany Date d'inscription : 20/02/2012

Frits Overmars a écrit:: Your power curve looks very good, Daniel. I am amazed that an engine making that much power would survive an ignition timing of 25° bTDC at max.torque rpm. Are you certain that this timing is correct? If yes, then the exhaust could be too short, but remember that I know virtually nothing about your engine, so I can only guess.

Thank you for the compliment!

Yes, I was skeptical about that ignition, too, but it is correct. With less advance the engine delivered less torque. The cylinder's angle areas might be too low for the revs that the exhaust would allow, so the ignition "forces" the engine to run at lower revs, where the angle areas are sufficient.

I think this explanation could be realistic, because my exhaust is ~6 centimeters shorter than the RSA's. But my exhaust timing is only a little bit shorter than the RSA's.

By the way: I dissambled cylinderhead + cylinder after ~50 dynoruns to look for detonation clues, because I was worrying about the durability with this ignition, too. But it all looked brand new and unused!

Howard Gifford a écrit:: I have a question for Jan. In your dyno testing the RSA (or any other engine) did you find that the engine seems to perform better at a higher rpm at the track than on the dyno? Our testing shows that our engines pull well beyond the point where they start to lose torque on ther dyno. Our best performance is around 10400 rpm but onb the dyno it peaks at 10,000. Our dyno is an eddy current Schenck W70 hooked to a Land and sea data aquisition system, I pump 3000 cfm fresh air into the dyno room. The ehhaust is vented outside well away from the intake air.
Could this be an air quality issue? It is not a tach problem as I have verified the data aquisition (mychron 3) against both tachs on the dyno. We also have to run 2-3 sizes richer at the track to get proper piston wash.
The engine is a 440 cc 180 degree twin cylindeer 65 mm bore 65.8 mm stroke.

My experiences are quite the contrary.
Always less revs on track.
At Garelli I had a ventilator blowing on the exhaust.
To see the same revs on track I had to wrap the exhaust!
Normally on the dyno the exhaust gets hotter than on track.
Can it be that your engine runs much better on track because of the lower inlet temperature?

Jan, Frits thank you for your answers.
Frits
my question you did not understand was ( maybe in better English ): Is there an interest to make B port higher than A port.

Others questions
what about C port same level than B port or a bit higher or lower?

On a reed valve engine is there an advantage to shorten the rear piston skirt to less disturb the inlet flow? when i say shorten is max 5mm.

Jan, the engine i have is the engine of a 125 RM (2003) so a bridged exhaust port
for this "old" MX bike the engine diagram is ex=191° and tr=128° transfert ports A and B on same level and C port is near 1mm lower.The cylinder is not standart the earlier owner modify it saddly a bit!!
thanks for you advise.

Pierre

Jan Thiel a écrit:

Ken Seeber a écrit:: Frits & Jan,

Just wondering if you ever pursued a desaxe offset in any of your engines and if there was any benefit?

Thanks

Ken

I always had the pistonpin offset towards the exhaust port.
Once I did try the difference when I worked at Bultaco.
Offset towards the exhaust port was the best.
Offset to the other side a little bit worse.
And the worst was no offset.

The piston is offset in the Aprilia RSA? How much?

That is probably the case. We run in very cold weather. I know cold air will give more power but will it increase the peak rpm of the motore. The egt temps are about the same in the dyno room and at the track

romeuh80 a écrit:

Jan Thiel a écrit:

Ken Seeber a écrit:: Frits & Jan,

Just wondering if you ever pursued a desaxe offset in any of your engines and if there was any benefit?

Thanks

Ken

I always had the pistonpin offset towards the exhaust port.
Once I did try the difference when I worked at Bultaco.
Offset towards the exhaust port was the best.
Offset to the other side a little bit worse.
And the worst was no offset.

The piston is offset in the Aprilia RSA? How much?

1mm.

Jan Thiel a écrit:

romeuh80 a écrit:

Jan Thiel a écrit:

Ken Seeber a écrit:: Frits & Jan,

Just wondering if you ever pursued a desaxe offset in any of your engines and if there was any benefit?

Thanks

Ken

I always had the pistonpin offset towards the exhaust port.
Once I did try the difference when I worked at Bultaco.
Offset towards the exhaust port was the best.
Offset to the other side a little bit worse.
And the worst was no offset.

The piston is offset in the Aprilia RSA? How much?

1mm.

I never had seen a piston with offset pin, or did not notice.... [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 6 55116

[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 6 55116

In theory why is better?
In my head the angle of attack is better just after tdc, and it would take more profit from the combustion but compression would extract more energy from the engine due to worst angle of attack.
Might the better combustion angle compensates for the worst compression angle?
This is not even thinking in timing changes....

Many thanks for this detail, never thought one day to have such knowlegde on 2 strokes....

Regards

hi. we have one problem on one of our racing scooters (cylinder malossi mhr team 50 at piaggio lc engine, 24mm pwk carb., ve force reeds, yasuni c30 exhaust). After about 2-3 motohours is damaged piston and head as you can see in the photos: [Vous devez être inscrit et connecté pour voir ce lien]
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where is the problem? My assumption is that we have little squish (0,5mm in 40mm bore and 39.3mm stroke, 85mm conrod), water temperature its 50-55°C , EGT (measured about 10cm from piston its 550°C). on other engines we also use 0,5mm squish and everything is all right (other engines use also malossi mhr team cylinder, one malossi mhr cylinder (without modular head), polini evolution cylinder and stage 6 alu cylinder...)

thanks very much

alcatelko a écrit:: hi. we have one problem on one of our racing scooters (cylinder malossi mhr team 50 at piaggio lc engine, 24mm pwk carb., ve force reeds, yasuni c30 exhaust). After about 2-3 motohours is damaged piston and head as you can see in the photos: [Vous devez être inscrit et connecté pour voir ce lien]
[Vous devez être inscrit et connecté pour voir cette image]

where is the problem? My assumption is that we have little squish (0,5mm in 40mm bore and 39.3mm stroke, 85mm conrod), water temperature its 50-55°C , EGT (measured about 10cm from piston its 550°C). on other engines we also use 0,5mm squish and everything is all right (other engines use also malossi mhr team cylinder, one malossi mhr cylinder (without modular head), polini evolution cylinder and stage 6 alu cylinder...)

thanks very much

The problems is the project of head ...
with the mini bike standard engine your problem is more frequently... because the head not is entered inside cylinder ... for this reason the head is not perfectly centered and engine detonates.
the bore head is more large respect at piston diameter, and you create accumulation of fuel... this causes detonation...

sorry for my english...

this thing is happening on lot of malossi mhr cyliders but in this one is piston life 2 mth...on the other same engine with the same cylinder is still first piston (about 20mth)...and other cylinders isn´t head entered inside cylinder and everthing its ok. we try bigger squish and if it doesn´t works we make new head...

alcatelko a écrit:: this thing is happening on lot of malossi mhr cyliders but in this one is piston life 2 mth...on the other same engine with the same cylinder is still first piston (about 20mth)...and other cylinders isn´t head entered inside cylinder and everthing its ok. we try bigger squish and if it doesn´t works we make new head...

i had the identical problem when my head is not centered inside the cylinder.
I solved inserting the head in cylinder of 1.5mm.
the only way to recover your cylinder is replaced the damaged part with bronze ring, but if your cylinder isn't born for to have interlocking head, you have very little chance that you do not happen again...

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

might also be an issue of too high compression, this is what happened on my 50 racer. squish seems not too low...

to center the head to cylinder you can also use axis housing and drill new holes in head + cylinder. this worked for me.

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

this is for sure the best version. but it also raises the timings...which is not always good.

head and cylinder are unmodified as they were unpacked from the box...so theoretical compresion ratio is about 15,5:1
timing will be good if the head will be put down of about 1mm...now its stock timing (about 190° exhaust)

» [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 2) (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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