i'm after advice on what thickness gaskets to order want to oder them and arp head stud kits this week. ive got a version 8 sti bottom end and version 4 sti heads any advice would be grateful even best place to buy and make, i was thinking cosworth or comitec?

 

well what was it mapped with or does it have to be mapped once built? thinner gasket will give higher comp ratio, lower comp ration is best for more boost but the amount that a gasket will change is not really important so choose witch one you think best. What kind of power you looking at?

 

its being mapped when built, im looking for between 350 and 400 with supporting mods.

 

Well cometic isn't 'really' needed , make sure the block surface is skimmed though along with heads if you want a good seal. Maybe the cosworth ones or some other after market gaskets that are around normal thickness? But as I said for comp ratio, if it hasn't been mapped yet, don't worry... what boost you looking at??? and do you have standard pistons???

 

not sure on boost really the bottom end is standard but had only done 38000 miles ive had heads and block faced so they both perfect.

 

All depends how much has been taken off the head and deck faces as to what your head gasket thickness will be so you need to measure the combustion chamber vols and piston deck heights to work it out correctly.
IIRC with standard head (STi V4) and deck heights, a 0.9mm MLS gaskets will give you 8.6:1 Static CR and a 1.1mm MLS gasket will come out at about 8.3:1 Static CR.
Personally I would go for the Cosworth gasket over the Cometic as the Cossie gasket seems to give a better seal on the fire ring area.

Mick