3.1 stroker? on boost?? ..anyone?

[dustyperez]

I am in the process of doing this build as well. I have looked and calculated for hours and hours. no pistons are quite right for the bigger stroke. you either need to shave skirts or tops of pistons, deck the block a large amount or use a super thick gasket.
here are some piston dimensions and whatever
http://cars.forumsee.com/a/m/s/p12-1...ion-ratio.html

IMO if your goin thru all this trouble why use a stock piston. Ive decided to got with cp's from vac. they are a little over 1k and they have all the specs already.

[Killacortes]

I probably want to say tired of M20. With 24v engines being cheap now, I would not even think about M20 3.1L. Even non vanos M50 is better than M20 3.1L.

Never go full retard

[nando]

You don't HAVE to bore the block anymore, you will still be at 3.0L (2979cc) with 84mm bore, but you will still need custom pistons because of the change in stroke. Since you have to use custom pistons anyways it would be pointless to not go to a bigger bore, IMO. 85mm will yield you a 3.1L M20 and 86mm will yield you 3.2L, although I hear the cylinder walls are dangerously thin for boost at 86mm.

people say this all the time, but there's no proof that 86mm is too thin for boost.

S54B32 has the same cylinder spacing as an M20, an even larger bore, and they work with boost just fine..

[nando]

If you want a solid bottom end that uses bolt on parts, I'd go for am M52B28 crank/rod/pistons. The piston crowns are thick so you can shave them down and cut new valve pockets for the 2v head.

if you want the S50 or S52 crank, you're pretty much stuck with custom pistons.

I probably want to say tired of M20. With 24v engines being cheap now, I would not even think about M20 3.1L. Even non vanos M50 is better than M20 3.1L.

you're on crack. Why even bother posting this kind of crap? If you don't like M20s, then just don't post in a thread about M20s.

[MF DOOM]

^^^Thank you for clearing things up.

[digger]

each 1mm gives approx 70cc on a 89.6mm stroke

[MF DOOM]

IIRC, boring .040 over will not raise your displacment by 1l. Youll get around .6l more? I have 85mm pistons in my m42 and it raised displacment to 1838cc. 1mm does not equal 1l.

[4evere30]

nothing else from another car would work?

[4evere30]

well then maybe ide rather just go will a 3.0l then and save myself the $$ for bore/bigger pistons ,one more question.... anyone know of another car that would have pistons that will work for a 3.0 M20? m54/s54 pistons work right?
but anything else?

(DAMN I WISH I TOOK THE PISTONS WHEN I GRABBED THAT M54 CRANK!!)

[SkiFree]

i think alot of the swedes use 86mm for boost so it cant be that "dangerous" but with boost there is no need to push the envelope as far as bore goes

I've had a number of sweds who have regretted going that big on an non-inspected block. Basically, due diligence is necessary when going over 85mm.

[digger]

its probably possible to find pistons from another engine and machine the crown down but seems like a pita.

i think alot of the swedes use 86mm for boost so it cant be that "dangerous" but with boost there is no need to push the envelope as far as bore goes

[SkiFree]

You don't HAVE to bore the block anymore, you will still be at 3.0L (2979cc) with 84mm bore, but you will still need custom pistons because of the change in stroke. Since you have to use custom pistons anyways it would be pointless to not go to a bigger bore, IMO. 85mm will yield you a 3.1L M20 and 86mm will yield you 3.2L, although I hear the cylinder walls are dangerously thin for boost at 86mm.

Well put, saved me 5min. typing the same thing.

[acolella76]

I'm aware of the 2.7 stroker combo but that doesn't really appeal to me for effort of a bottom end rebuild , so to use the 3L crank I HAVE to bore the block and get custom pistons then?
Suggestions on good pistons for this?

You don't HAVE to bore the block anymore, you will still be at 3.0L (2979cc) with 84mm bore, but you will still need custom pistons because of the change in stroke. Since you have to use custom pistons anyways it would be pointless to not go to a bigger bore, IMO. 85mm will yield you a 3.1L M20 and 86mm will yield you 3.2L, although I hear the cylinder walls are dangerously thin for boost at 86mm.

[einstein57]

No effort. You go to the yard and grab a super eta block and just replace the rod bearings. Slap on your head and your done. $200 build that can be completed in 1 day. Either that or spend $2k on a proper bottom end build. Your choice.

[4evere30]

I'm aware of the 2.7 stroker combo but that doesn't really appeal to me for effort of a bottom end rebuild , so to use the 3L crank I HAVE to bore the block and get custom pistons then?
Suggestions on good pistons for this?