This would be on a boosted motor making about 250-300whp. I would like to lower the compression like .3-.5 Also this motor has forged pistons already and is sleeved. My friends motor is at 10.3:1 now and he's trying to get it down to a 9.8:1 but doesn't want to go through buying a new set of pistons. I'm sure i can find a headgasket to do this, i just wanted to know what the disadvantages of lowering compression like this is. thanks guys

 

You screw up the quench pad clearance between the piston and cylinder head. The quench area is used to provide detonation resistance. This is one of the reasons some people's low compression motors didn't work out well for them, they improperly engineered the clearances and provided insufficient quench, and couldn't raise the boost to the limits needed to offset the lower compression. You should clay the motor and measure the clearances. I guess you will have to weld material to the quench pads on the head to make up for the thicker HG.

I've never really done up a motor with a thicker HG and stock piston, but I know its one of the things i'm aware of when putting a fresh one together!

 

So are you saying the thicker headgasket will be more prone to blow out? I am not talking about some crazy thick headgasket, probably something like .05 mm in thickness or so. I am 100% confident in assembling the motor, this is just the first time i contemplated using anything besides an oem gasket. I don't see much talk about using headgaskets to lower compression and to be honest i have no idea if it would be a reliable alternative to buying new pistons, but my friend is pretty set on doing it that way so i guess i will have to wait and see. If anyone has any other info or tips please feel free. thanks

 

Do some research on the importance of the quency pads to aide in your decision.

 

If you're going to have the head off, you could always clean up the chambers. Taking enough material off can reduce your compression without screwing up quench. Get a 3-angle valve job while you're at it.

 

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Man your trippin', really. Welding the Head to run a thicker headgasket?

Geez...It's not going to be prone to more detonation. Call Inline Pro and try telling them what you just posted and they will laugh at you.

Yea, quench is important...but these motors have very efficient combustion chambers and putting a slightly thicker headgasket will only help.

 

will do on that research for quench pads

beepy, downtime is a pretty big constraint. the motor isn't apart, he's driving around with it. The original plans were for a nitrous setup, but now things have changed. I can swap the headgaskets in about 6 hours, machining the head would take a few days at the least. My friend needs the car down no more than a weekend.

Superdave i take it you have you went this route before with no problems?

 

IT's fine, Just get a headgasket that makes sure that it's stock bore and of metal, like O.E.M, TODA, or Cometic

 

hmm i'm finding alot of intresting information on the quench pad area. Just out of curiosity, would using a headgasket to bump compression have just the opposite effect?