Can I safely run a head with 84.5mm chambers on an 84mm block? Im rebuilding my setup and picking up a ported head but it has enlarged chambers. I know its safe to run stock head chambers on larger bore but what about the other way around?

 

i would say it might have some sealing issues with the head gasket. im not a hundred percent sure on that but on smaller chambers/larger bore none of the head gasket would be exposed since the head gasket is made to fit around the cylinder but on one with larger chamber/smaller bore some of the head gasket would be exposed in the actual chamber which could lead to problems.

 

That would only be true if an 84mm head gasket were used. I could simply use an 84.5mm head gasket as that is the true sealing circumfrence anyways.

 

i dont think you will have problems, most people use headgaskets that are within .5mm

 

Thanks Saxon. I would tend to agree, especially since the diffrence is so small. Its not like Im putting it on an 81mm bore. ha

Im debating if I should just bore it to 84.5mm and go with high comp pistons anyways. Im thinking 11.5:1 on E85 should be doable. Im looking to push deep 500s next year.

Are used pistons even worth anything to sell? I have swaintech coated CP 84mm 9:1 pistons now. Otherwise I'll just reuse them but Id like to match the bore to the head AND go with higher compression. What do you think?

 

if you have the cash flow i would go 12:1 and sell the old

they probably arent worth a whole lot, but if there isnt much wear on the skirts im sure someone will buy them for a cheap b20 build

 

Saxon, sold the old pistons for half price. Now looking at high compression pistons. Compression will be about 11.6 with the Wiseco 84.5mm 8.25cc dome piston. Should I copper O-ring the block or can I get by a standard head gasket?