got a head here 2wd cosworth YB which measures 137.5mm would you say this has had its day? or would it be ok to use with maybe a WRC gasket if so what mm gasket?

 

I going to use one which is 137,2mm. Use pistons with valve pockets and measure everything to calculate c/r. Wrc cars and rallycross cars run heads like this to raise c/r and run between 350 and almost 600bhp for rallycross so that will do for me.

 

thanks for the reply buddy yeah i was just a little concerned that my valves would clash with my pistons. so you rekon get my pistons pocketed?

 

Yep pocket pistons but make sure you cc it. Then have you map adjusted to suit.
Also its advisable with any skimmed head to have adjustable pulleys to get timing back to spec.

Regards
Paul

 

great advice here thanks for that mate

 

Yes thats how you need to do it.
Dont be afraid to raise c/r to 8.5 or even 9/1, mapping is the most important bit to keep it in one piece.

 

The head thickness limit of 138.68mm quoted by Cosworth has nothing to do with compression ratio guys, its the limit cosworth quote as the absolute max material removal allowed before you compromise the valve seat integrity.

 

so stu do you rekon i will be ok using the head at 137.5mm providing i use pocketed pistons and a group A head gasket? thanks.

 

If the max is 138.6 and you are under then surely it will be at the risk of valve seat integrity, I guess that then comes down to spec of engine, boost, usage, revs etc. I bet the factory have a large tolerance of safety.

 

The Mountune works WRC engines had thinner than 138.68mm heads fitted when built from new.

Steve

 

cool i will go ahead with the build and hope for the best thanks lads

 

right this is my last chance as i will be assembling the engine tomorrow so just to build my confidence. I should get no valve to piston contact providing my pistons are pocketed and i use a victor reinz group A gasket. nervous thats all im asking again for lol. Thanks.

 

When its all built up mate I'd avoid bouncing off the rev limiter as when the heads are that low there's not a lot that holds the valve seat in place which is why you see so many drop valves into cylinders.

 

thanks for the reply mate. Yeah i will be lets say taking it easy as that will be in my head at all times. i basically want reliability more than anything now so i can just enjoy the thing for once lol.