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Il y a en vrits 30 utilisateurs en ligne:: As aluminum has a higher dilation coefficient than iron cast, I would have left a less tolerance between the cylinder and the sleeve, it’s correct? But the best solution would be to use a conical fit, like Jan Thiel did on his last sleeved Jamathi cylinder. Jan used a morse cone angle on both the sleeve and the cylinder. The tolerance was thus that only the last millimeter required a slight press fit.

It was equally easy to remove the sleeve again. Your reaction makes me happy for more than one reason. Dont feel guilty about frenck guys Frits. We are very proud to have you on Pit-Lane!

Hi Frits,Hi Jan; Please check my picture. You see this 2 points on the piston for sure. Any idea to prevent or eliminate this?

Hi Frits,Hi Jan; I hope you remember the 2 points on the piston crown. Frits i hunt the bird out of my office Please find here more details concerning the port angles. If you had posted this picture yesterday, I would have been sure it was an April joke. No, I’ve never seen something like this before. Jan, what do you make of it? Ik looks like a bird dropped something just before Vortex closed the engine.

Frits, I’m very overmaars. Hahaha Frits, No april joke and no bird in my office. 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 rpm, but the engine would not rev.

It would just stop firing at about We tried everything we could to make the engine rev with a 0,55 squish. Even 0,65 was negative! The overmxrs would touch with 0, So the ‘real’ squish at high rpm was 0,25 mr Thiel do you meanwith small squish gap less than0. 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.

Bucket Racing Fabrication

Or the fresh mixture did not reach the spark plug frifs. Maybe too much turbulence? That is what I think! You can also reach a point where the blowdown becomes insufficient. Then the engine feits firing through lack of fresh mixture.

You’ve written that you tried everything with 0,5 mm overkars gap to make engine rev, but it didn’t work. Have you tired a smaller squish band area ratio? Yes the piston becomes too hot because the shock waves of the detonation blow away the boundary layer of gas that normally forms a heat insulation on the piston surface.

Piston domes covered with ceramic or titanium have been tried but the problem is that the dome surface then stays much hotter which causes even more detonation.

This was when testing unleaded fuel, in ftits This was when testing unleaded fuel, in Jan before the unleaded era what did you consider to be the frita head form. I thought that it is not the way to prevent detonations.

Would this be somekind of best average? Can you tell’s us something, or some ideas about what’s behind of this concept? Remember, it is called the FOS simple exhaust concept ; I developed it for young people who are just starting to learn about two-stroke tuning, and who haven’t yet got much theoretical knowledge.

Frits, I have a rather unconventional question; is the thrust of the exhaust gasses exiting the exhaust system ever considered on fris race bike? If so, what would be an raw estimate of the thrust produced, let’s say on a GP machine?

On a race bike not really. Let’s do a raw estimate: Since the exit is pointing rearward anyway, that is some help, but nothing to write home about.


There is an other form of motorsport where thrust plays an important role: Last year a drag racer said to me: The exhaust pipes are angled up pvermars such a way that this thrust gives an optimal balance between forward thrust and downforce on the driving wheels.

Frits Overmars Expansion Chamber aka FOS exhaust concept

Calling RAW Rick you there? For sheer numbers and spectacle now much surpasses the Top Fuelers. Interesting Eccelstone was bemoaning the lack of noise from the lastest F1 cars, Bernie thinks he can change the exhaust for more noise. I wonder if he realises that the turbo uses energy from the exhaust and that’s where the noise has gone.

Eccelstone was bemoaning the lack of noise from the lastest F1 cars, Bernie thinks he can change the exhaust for more noise. Eckie had been warned about the noise reduction over a year ago. He didn’t react then.

Maybe he thought he could bend the laws of physics by trits telling them loud enough how he wanted things to be. Frits, thanks for the clarification!

Some top Fuel Dragster numbers, from a standing start 0. Bernie has bent many things in the past rules and laws I suppose vrits thought he might try physics. This was when testing unleaded fuel, in Thanks Jan!

I thought that because of the squish gap which was smaller than 0, 7 mm, the squish velocity became too high and because of it the rev.

Bucket Racing Fabrication

If the squish band ratio is smaller then the squish velocity will be lower. But according to the abovementioned I suppose I was wrong. Frits Overmars Nombre de messages: Overmarss, Holland Date d’inscription: Jarno Nombre de messages: Imatra sur Seine Date d’inscription: Vortex Nombre de ovwrmars Piquer Nombre de messages: Manuel Rainer Nombre de messages: Forgi Nombre de messages: Jan Thiel Nombre de messages: RAW Nombre de messages: Leiria, Portugal Date d’inscription: Institute of TwoStrokes Nombre de messages: LucF Nombre de messages: Pays Bas Date d’inscription: Page 1 sur Permission de ce forum: