iJust want my gasket to be able to survive an overheating incident. So iJust ordered a 90mm Cometic from JGY. Now either way i`m using this gasket, but there are some questions I can`t answer: Firstly, will it reduce compression any? iKnow that`s the point of a turbo gasket, is this one any thicker than stock? Secondly, is 90mm the right size? It`s the smallest they had...

so sue me for doing it the wrong way but iNeed a headgasket yesterday and iFigure this should work enough to get the car running regardless of performance. If it does reduce compression, i`ll just be doing the single cam piston mod sometime soon.

 

the 90 mm head gasket id for motors that have been bored out and bigger pistons installed... the cometec gasket should not drop your compression any if it is standard thickness...

using this gasket with a stock bore could cause some problems with combustion as there is a gap between the head and the block... this could actually cause the head gasket to fail faster than normal... and in a boosted application could cause the headgasket to fail faster than a na application...

 

out of curiousity and if im ever in the same situation, whats the right size headgasket?

 

89mm is stock gasket..........
89.5mm if you have bored at .020............ CR drops 2 points from stock OEM CR
90mm if you have bored at .040.......... CR drops 4 points from stock OEM CR
Boring decreases compression, destroking depending on the dish volume will more than likely increase CR, that is why when most people bore out KA they go with higher compression pistons from the 1990 sohc.

This follows for 91-94 KA CR....
1990 SOHC pistons bored at .020 10.9:1CR
1990 SOHC pistons bored at .040 10.7:1 CR
1990 SOHC pistons "no Bore" 11.1:1 CR

With pre 89 SOHC pistons add 2 points to the CR, 89 pistons have a raised dish of .020 and is not recomended unless a thicker gasket is used, valves fall under the .015 "safe" distance from TDC, so a thicker gasket other than the OEM is recomended.......

The CR rating can change depending on the thickness"depth" of any after market head gasket........

I believe those are the CR ratings, may not be completly accurate due to different thicknesses in gaskets, I could be slightly off......
I don't have any charts infront of me right now............

 

shoot. thanks, vin and wik`d...

but unfortunately that means iHave a brand new Cometic MLS gasket that`s of no use to me. classifieds time, iSpose.