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Discussion Starter #1
Alright, so I have a d16y8 that was fully built for high compression. The head gasket on there now is a Cometic 0.027" (stock was 0.037").
The current compression ratio is about 11.0:1. I will be boosting this motor in the winter. I wanna lower the compression to around 10.0:1 - 10.2:1. I don't know exactly what size head gasket will yield the compression ratio I'm looking for, but I know where to find out.
I'm just concerned about using too thick of a head gasket. My power goals are ~280whp on 10-11psi out of a gt30r. How thick of a head gasket can I safely run with that setup? What are the dangers of going too thick?
 

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I would call Cometic and ask them. They can make anything you need. I would think you should be ok with up to .080 or may be more Cometic should be able to tell you.
 

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wouldnt it be safer to swap pistons out?
 

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ehhh...it really depends how much power he's trying to make.
 

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I wouldn't have thought that a 10:1 CR would be all that hard to tune on.
After all, a stock Y7 runs 9.4:1 and a Y8 is around 9.6:1....So is that 0.4 CR increase going to be such a ball ache to tune?
 

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I'm gonna have to agree and say change the pistons. If you want to reliably make power using boost you might as well pony up the 500$ for the Vitara pistons and JE rods kit on Ebay. Now that I think about it, it's not even 500$ and you'll be able to make well over 300whp if you get boost happy. :D

EDIT: That is assuming they used stock rods in the initial build. If they didn't then just buy some Vitara's.
 

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I wouldn't have thought that a 10:1 CR would be all that hard to tune on.
After all, a stock Y7 runs 9.4:1 and a Y8 is around 9.6:1....So is that 0.4 CR increase going to be such a ball ache to tune?

Yes it's difficult to tune at higher compression ratio's. That's common knowledge. You can make more HP with higher c/r's but you also increase the risk when the tune isn't perfect.
 

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Discussion Starter #19
Thanks for all your posts guys. I really don't wanna change the pistons. They don't have more than 10k miles on them. They're srp forged dish top pistons, so I'm not entirely worried about detonation in the 10:1cr range and relatively low boost. I know a precise tune will be needed, but I'd rather shell out a few hundred buck for an awesome tune than for new pistons.

I really just wanted to hear from poeple who have had experience with exceptionally thick head gaskets. I'll call Cometic soon and ask what they recommend. If they tell me anything truly enlightening, I'll share the knowledge with you guys.

Keep the posts coming!
 

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i've heard nothing but bad stories from local cometic headgasket owners . using a super thick jumbo headgasket to lower your compression ratio is a terrible idea. especially if your taking a setup that was MADE for high comp NA and are trying to cheap-ass your way to a low/med compression boost setup.

do this instead. pull the pistons, sell them for money. take that money and spend half of it on vitara's, and an OEM hg and put the other half towards your tune.

btw, i've daily driven my self tuned 10:1 compression y7/y8 stock bottom end, boosted on 8lbs for 2 years now with no issues ;-)

-Luke
 
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