Ist das so richtig ?

[KTy]

I am about to drill some holes in my GS piston for 133cc cylinders.

I do not really know if it is really worth it, I want your opinion...

The goal is to use the idea behind the "Malossi Patent" to help cool down the piston and reduce gaz inertia...

I want to drill 4 holes in green, and also maybe some holes in red in front of the transfers of the 3rd port (or lateral ports ?)

Bearbeitet 20. Mai 2007 von KTy

[pfupfu]

what about the cutout?

[Bertl]

The green holes won´t work on a Polini, unless you grind the cylinderwall above the boostports about 2cm upwards. Instead of the red holes i would put in one large hole (like the original Polini).

I´ve done it this way on my Polini:

[Brosi]

For which cylinder? Malossi or Polini? If Polini: I just copied the original Polini boostport window:

Concernig the CVF holes: I didn´t do that for several reasons, one being just lazy. But I´ve seen several examples where the holes where cut.

[amazombi]

i personally believe the cvf thing was more of a marketing measure than a true performance must. i can't remember seing a single other two-stroke piston which has it, and unless i'm mistaken, even malossi has dumped it on anything but their oldest designs, that's their vespa stuff. no idea why one would want to spend time and effort on that. as far as i remember bbg has proven that a polini is good for 24 brake or so (at comparatively low rpm), which, in my book, equals a pretty high bmep, hence i guess that even more power would be possible at slightly higher rpm.

[KTy]

Thanks for the replies.

The base was a Polini 133.

AFAIK, I do not really need a window in my piston to feed the 3rd transfer because of my engine configuration. Right ?

However, I wanted to drill these holes for better cooling, by continously renewing the gaz under the piston head... But it does not seem to be so popular...

My piston already looks like this:

http://ktylife.free.fr/vespa/KTy133/KTy134...Pr%e9par%e9.jpg

Could it be bad (for pre-compression for instance) if I drill the "green" holes (as previously proposed) ?

Or to put it shorter, what else could I do to improve perf. and/or reliability ? A big 3rd transfer window and smalls holes between transfers for lubrification ? Useless/Waste of time ?

Bearbeitet 21. Mai 2007 von KTy

[Brosi]

Right. No additional bostport windows needed.

Cooling, hmm. I don´t know. I think it´s vain endeavour, because Polinis usually are thermically rather stable anyway.

For Malossi cylinders some people adapted drilled these CVF holes. e.g.: JOB´s piston

[gertax]

Or to put it shorter, what else could I do to improve perf. and/or reliability ?

go jet that thing until you're sure it's absolutely perfect

[amazombi]

go jet that thing until you're sure it's absolutely perfect

sounds good to me.

have you had it on a dyno yet? maybe it is pretty powerfull as it is already. and keep in mind that for esc racing you may not want max power in the first place anyway.

[KTy]

No dyno yet....

Exactly, if I am wondering about all this, it is mainly for reliability...

Ok, I guess I will let it this way ;)

I hope I can make it to the ESC Class2, I will have to operate my fuffi in my 1,5x2m cellar !! :-D

If not, Class 5

[KTy]

For which cylinder? Malossi or Polini? If Polini: I just copied the original Polini boostport window:

Concernig the CVF holes: I didn´t do that for several reasons, one being just lazy. But I´ve seen several examples where the holes where cut.

The 2 holes above the window are aligned under the rings "spigot", rigth ?

The purpose is cooling of the cylinder wall ?

[absolut]

The purpose is cooling of the cylinder wall ?

Yes for cooling. But if it is needable on the "intake side", I don´t know.

Normally you drill it on the "outtake side" because it´s the hotter one.

Bearbeitet 3. Juni 2007 von absolut

[Brosi]

Yes, I have 4 of them on the exhaust side. I´m not sure, how good they work,bBut at least several stock pistons have them, too. So at least it´s for salvation of consciences.

And the lubrication holes are positioned at the studs, being the preffered position of heat seizure.

Bearbeitet 3. Juni 2007 von broz666

[KTy]