Compression

[sinistaGTR]

Hey guys,

i just bought some wiseco forged pistons 87mm bore (rb25det), now on the wiseco site it says that these pistons bring comp ratio down to 8.0 to 8.4, my question is what size head gasket to get, acl only make a 1.2mm one. im going to be running a gt3040, power fc, q45 afm. i want to run bout 25psi max just worried that a 1.2mm head gasket wont be enough but would the pistons bring the comp ratio down enough to do this.

[Godzilla32]

best to do the sums and work out your compression ratio. Then you can choose an appropriate head gasket. Standard thickness will probably be fine if the pistons are already reduced comp.

[sinistaGTR]

well what sorta sums.... i mean if the comp ratio with the pistons is going to be 8.4 then just wondering if the 1.2mm head gasket will be fine with that sort of boost, or to go thicker....

[Godzilla32]

Im still learning. Not qualified as yet. Hopefully someone else can tell you what the correct formula is and what will be necessary to acheive safe combustion.

[Craved]

heres a handy site

http://www.csgnetwork.com/compcalc.html

[sinistaGTR]

Thanks Craved, tried using that calculator and couldnt figure it out. Bit unsure about the CR.

Is there anyone else that has done similar mods? Just want to know if i can use the 1.2mm head gasket safely on this setup...

[MR331307]

Thanks Craved, tried using that calculator and couldnt figure it out. Bit unsure about the CR.

Is there anyone else that has done similar mods? Just want to know if i can use the 1.2mm head gasket safely on this setup...

run the 1.2 headgasket

run the 1.6 or 1.8 if you wanna lower the comp

Decking the block and machineing the head also make a difference by raising comp

if ur are decking the block as well as machineing it run a 1.4 or 1.6mm thick headgasket

Edited October 19, 2006 by MR331307

[drgnball34]

I have also orderd wiseco 40thou pistons. Still confused as to what thickness gasket to uses also. A mechanic told me it is best to use standrard size gasket and get the head machined to suit? I have GT2835pros and will be running approx 22psi. Not exactly engine friendly. Would a comp ratio of say 8.6 be suitable? I want the saftely but also want to maintain the response. Obviously to bring the comp up i would need to machine the head anyways or get a thinner gasket which i think wouldnt be the safes option.