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

Hi,
Dear Jan;
I made some test with the squish band always with the same combustion volume (9 cc) and it seems that narrower the squish that more the squish angle has to open, otherwise the rev. ability go worst passing 13000 rpm to maximum 15000 rpm.
Do you agree to this?
A parallel squish band needs more distance.
The best result for me was 0,70mm squish with 1,5 degree upgoing with a 4 degree domed piston.

Thanks again Jan and Frits sharing your knowlege with us.

Vortex a écrit:: Hi,
Dear Jan;
I made some test with the squish band always with the same combustion volume (9 cc) and it seems that narrower the squish that more the squish angle has to open, otherwise the rev. ability go worst passing 13000 rpm to maximum 15000 rpm.
Do you agree to this?
A parallel squish band needs more distance.
The best result for me was 0,70mm squish with 1,5 degree upgoing with a 4 degree domed piston.

Thanks again Jan and Frits sharing your knowlege with us.

Our best results were with 0,7 parallel squish.
But we never tried to reach 15000 rpm.
Gear shifting was done at 13250.
The engines were tested until 14500.

Vortex a écrit:
Hi,
Dear Jan;
I made some test with the squish band always with the same combustion volume (9 cc) and it seems that narrower the squish that more the squish angle has to open, otherwise the rev. ability go worst passing 13000 rpm to maximum 15000 rpm.
Do you agree to this?
A parallel squish band needs more distance.
The best result for me was 0,70mm squish with 1,5 degree upgoing with a 4 degree domed piston.

Thanks again Jan and Frits sharing your knowlege with us.

Our best results were with 0,7 parallel squish.
But we never tried to reach 15000 rpm.
Gear shifting was done at 13250.
The engines were tested until 14500.

Ok, thank you.
In kart, gear shifting is done near 14300, i suppose it is due to the 30mm carb the minimum volume of 11cc and the homologated
fix ignition curve that we have to rev higher.

Nombre de messages : 11 Localisation : Slovenia Date d'inscription : 27/03/2013

Frits Overmars a écrit:

ice t a écrit:: I did some measuring today and realized i can't make such a big radius like the left drawing because the timings would be to big. What do you say for the right drawing with the black line for corner radiuses and a nice chamfer radius on the upper port edge.

Define 'a nice chamfer radius', ice t. If you make the radius large enough, you don't need an elliptical port roof at all.
But 'nice' won't work in a formula.

I was thinking of a 1-1,2 mm radius above the port edge ,almost geting the shape of the desired elliptical port . Would a straighter port roof with a radius give a higher power output than a eliptical one ? It sure has more port area. I also don't have auxiliary exhaust ports so every port area i can get is good.

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

Jan Thiel a écrit:

Manuel Rainer a écrit:

hi

Jan in part 2 page 12 you talking about the squish in the RSA:

Jan Thiel a écrit:: The 0,7mm squish was the minimum we could use with good power at high pm.
Less squish gave more power at low rpm, until 12000 rpm, but the engine would not rev.
It would just stop firing at about 13500
We tried everything we could to make the engine rev with a 0,55 squish.
Impossible! Even 0,65 was negative!
The piston would touch with 0,45.
So the 'real' squish at high rpm was 0,25

did this test where made always with the same combustion chamber? if yes, do you increase the compression ratio by reducing the squish gap.

did the engine dont want to rev of the fact of to high compression ratio?

thanks Manuel

No Manuel, the squish was varied maintaining the same compression ratio!
Doing it otherwise would not be serious!

hi

I thought so, you always has tested the things the right way.

my question was only because i have seen that in my 125 Kart engine if i rise the compression up to 16:1 or more the engine dont want to rev over 13800. also if the squish was 0,8.

so i thought compression near 16:1 with 95er pump petrol dont let the engine rev, dont matter what squis gab.

thanks

Manuel

by changing your squish gap you'll change the amount of heat in your pipe, so you can also change your over rev by this way

Jan Thiel a écrit:
The 0,7mm squish was the minimum we could use with good power at high pm.
Less squish gave more power at low rpm, until 12000 rpm, but the engine would not rev.
It would just stop firing at about 13500
We tried everything we could to make the engine rev with a 0,55 squish.
Impossible! Even 0,65 was negative!
The piston would touch with 0,45.
So the 'real' squish at high rpm was 0,25

mr Thiel

do you mean , with small squish gap(less than0.65mm on the rsa), it can stop the firing of the spark plug ?

pagi a écrit:: Jan Thiel a écrit:
The 0,7mm squish was the minimum we could use with good power at high pm.
Less squish gave more power at low rpm, until 12000 rpm, but the engine would not rev.
It would just stop firing at about 13500
We tried everything we could to make the engine rev with a 0,55 squish.
Impossible! Even 0,65 was negative!
The piston would touch with 0,45.
So the 'real' squish at high rpm was 0,25

mr Thiel

do you mean , with small squish gap(less than0.65mm on the rsa), it can stop the firing of the spark plug ?

Stopping the firing would have broken the ignition coil I think.
That is what happened when we once tried a spark plug without mass electrode.
This gave more HP, until the coil broke!
But maybe the spark did not ignite the mixture anymore.
Or the fresh mixture did not reach the spark plug anymore.
Maybe too much turbulence?
That is what I think!
You can also reach a point where the blowdown becomes insufficient.
Then the engine stops firing through lack of fresh mixture.

Manuel Rainer a écrit:

Jan Thiel a écrit:

Manuel Rainer a écrit:

hi

Jan in part 2 page 12 you talking about the squish in the RSA:

Jan Thiel a écrit:: The 0,7mm squish was the minimum we could use with good power at high pm.
Less squish gave more power at low rpm, until 12000 rpm, but the engine would not rev.
It would just stop firing at about 13500
We tried everything we could to make the engine rev with a 0,55 squish.
Impossible! Even 0,65 was negative!
The piston would touch with 0,45.
So the 'real' squish at high rpm was 0,25

did this test where made always with the same combustion chamber? if yes, do you increase the compression ratio by reducing the squish gap.

did the engine dont want to rev of the fact of to high compression ratio?

thanks Manuel

No Manuel, the squish was varied maintaining the same compression ratio!
Doing it otherwise would not be serious!

hi

I thought so, you always has tested the things the right way.

my question was only because i have seen that in my 125 Kart engine if i rise the compression up to 16:1 or more the engine dont want to rev over 13800. also if the squish was 0,8.

so i thought compression near 16:1 with 95er pump petrol dont let the engine rev, dont matter what squis gab.

thanks

Manuel

Sorry Manuel,
But how can you reach a compression ratio of 16:1 with a kartengine with a min. volume of 11cc with a in this engine normaly used mainexhaust diagramm of something between 195 and mabe 197 degree?
The corrected one is for sure under 10:1!
For me Mr. Thiel is right when he wrote; The fresh mixture did not reach the spark plug anymore.
Maybe too much turbulences?

Jan or Frits, do you think a 120mm con rod would yield similar benefits on a piston ported engine. Having optimised ignition, Carburation, etc. And the same for reed engine ???
Jan mentioned earlier on the forum about 50cc engines with long rod ratio, were they piston port, disc valve, or reed.
Thanks in advance aprilia - [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 39 809262

aprilia - [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 39 809262

Paul Gane a écrit:: Jan or Frits, do you think a 120mm con rod would yield similar benefits on a piston ported engine. Having optimised ignition, Carburation, etc. And the same for reed engine ???
Jan mentioned earlier on the forum about 50cc engines with long rod ratio, were they piston port, disc valve, or reed.

Paul, you mention a 120 mm rod and you mention 50 cc engines. Am I to understand that you want to try a 120 mm rod in a 50 cc engine? It certainly won't be too short then Wink

.
When I see a 120 mm rod length I think of a 125 cc engine, so let's assume that is what you are talking about. And then I agree with Jan that this rod length will work irrespective of the type of induction system.

Frits, thanks. I was referring to a 175x2 (TZ350). I remembered Jan saying about rod ratios on 50cc, I should have made myself clear.

Nombre de messages : 44 Localisation : Portugal Date d'inscription : 08/11/2011

If I'm not mistaken the derbi 50cc engines had a 90mm rod from factory, and I read here and in some other sites that when you kept the 50cc the engine gained a bit more "breath" when using a 84-85mm rod.

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

Vortex a écrit:: Sorry Manuel,
But how can you reach a compression ratio of 16:1 with a kartengine with a min. volume of 11cc with a in this engine normaly used mainexhaust diagramm of something between 195 and mabe 197 degree?
The corrected one is for sure under 10:1!
For me Mr. Thiel is right when he wrote; The fresh mixture did not reach the spark plug anymore.
Maybe too much turbulences?

hi

i am not driving official races. there is no limitation of head volume.

i got to 16:1 in my 125 TM KV95 rotary valve engine, with a head volume of 8,3 cc. ex on 197° squis gab 0,8. in this case the engine not want to rev over 13800.

Manuel Rainer a écrit:

Vortex a écrit:: Sorry Manuel,
But how can you reach a compression ratio of 16:1 with a kartengine with a min. volume of 11cc with a in this engine normaly used mainexhaust diagramm of something between 195 and mabe 197 degree?
The corrected one is for sure under 10:1!
For me Mr. Thiel is right when he wrote; The fresh mixture did not reach the spark plug anymore.
Maybe too much turbulences?

hi

i am not driving official races. there is no limitation of head volume.

i got to 16:1 in my 125 TM KV95 rotary valve engine, with a head volume of 8,3 cc. ex on 197° squis gab 0,8. in this case the engine not want to rev over 13800.

Hi,
Ok that changes everything.
How much advance do you use?
Did you try more squish?
Which exhaust temp. do you reach?

Manuel,

Get a PVL 5000 wind stator, it has 11 degrees of retard in it and looks the same as the straight line 1850 wind one.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

hi frits can i ask you about this pipe ? im trying to make it from the FOS. do you think the HP and target rpm values seem correct or they need to be higher ?

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i dont understand how the pipe will connect to the engine. my exh flange bolts to the cylinder and goes inside the pipe. so does that meen i have to make a flange on the pipe thats bigger than the exh flange ? but will this meen the pipe now has to be shorter to make up for the added flange length ? i have 2 example pics but im not sure which is correct

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also i dont understand about the stinger portion. why do they have it bigger than the ending diameter of the last cone ? or is that a muffler ? how can it be 25.6mm diameter of the ending cone, then immediatly 39mm at the stinger ?

thnx frits if you can help aprilia - [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 39 771973

aprilia - [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 39 771973

brokedown a écrit:: hi frits can i ask you about this pipe ? im trying to make it from the FOS. do you think the HP and target rpm values seem correct or they need to be higher ?

Brokedown, I now know three things about your engine: bore, stroke and exhaust timing. That is not enough to establish target power and rpm values. Besides, even if I had all the necessary data (over a hundred of them), I could not afford the time.
I also noticed that you calculated the exhaust dimensions using some program that may or may not be based on my simple exhaust concept. I have no way of knowing whether these programs function correctly, so I cannot take responsibility for their output, as I have repeatedly stated here.

Citation :: also i dont understand about the stinger portion. why do they have it bigger than the ending diameter of the last cone ?

The reason is to make sure that the end cone restriction alone influences the outflow.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

thnx frits. the engine is a modern 300 mx. the program was from underdog. i thought you mentioned before that is was a reliable program to use ? if not then what do you recomend so i can make a pipe

That is exactly what I posted my simple exhaust concept for. You don't need someone else's program to work that out.
The only math in the formulas is a square root. How hard can that be?

Frits, the cooling system on the RSA125 is clearly very efficient. Were there any problems with cavitation with the high flow water pump? What pressure rad cap was used ?
PS I completely missed the subtle humour in your reply to my question is about 120mm con rods. I've read this thread from end to end at least three times, and have laughed many times at the humour in you posts. You got me there. lol!

Paul Gane a écrit:: Frits, the cooling system on the RSA125 is clearly very efficient. Were there any problems with cavitation with the high flow water pump? What pressure rad cap was used ?

I don't recall the cap pressure but it must have been high enough to prevent cavitation despite the large coolant flow.
On the other hand, cavitation often does not become noticeable during the life span of a racing engine. It's not like a passenger car engine with a couple of tons on the clock and a hint of nibbling at the cylinder head casting.

Citation :: PS I completely missed the subtle humour in your reply to my question is about 120mm con rods. I've read this thread from end to end at least three times, and have laughed many times at the humour in you posts. You got me there.

My pleasure; that is what we do it for (and a bit for two-stroke encouragement) Wink

.

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1.8 c'est écrit dessus. En bar, je suppose. Ce me semble beaucoup, effectivement ?

Oui effectivement le clapet du bouchon de radiateur se soulève pour dépressuriser le circuit de refroidissement dès 1.8 bar, mais pourquoi, hé bien tous simplement, nous savont que la température d'ébulition de l'eau en circuit fermer est retarder, ou plûto est contenue dans ce cas.

Emmanuel Laurentz a écrit:: Oui effectivement le clapet du bouchon de radiateur se soulève pour dépressuriser le circuit de refroidissement dès 1.8 bar, mais pourquoi, hé bien tous simplement, nous savons que la température d'ébullition de l'eau en circuit fermé est retardée, ou plutôt est contenue dans ce cas.

Manu,
Dans le cas présent, heureusement, la température de l'eau n'atteint jamais la température d'ébullition !
La pression appliquée sur le liquide de refroidissement est destinée à retarder l'apparition de la cavitation dans certaines zones.

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