What thickness MHG should I get?

[Supraflymk3]

I have a 7M-GET and I just blew my headgasket. I don't want to throw another OEM one on it because I'll probably blow it again. I have ARP Head Studs. The head is brand new 15,000 miles ago. Its not warped so I won't be having it shaved. The block surface is still in really good shape the engine has 70,000 miles on it. My question is how thick of a metal headgasket should i get to lower my compression ratio closer to stock turbo levels? I know you guys are going to tell me I should deck the block but I have put mhgs on some older supras of mine without doing that and never had any problems with blowing them. so leave that out please. if it does blow again then its my fault but i don't think it will.

 

[GrimJack]

How thick of a gasket is a simple calculation. You need to know how much has been shaved off the head and the block, add that to the stock gasket thickness, and pick the closest MHG thickness you can get from there.

If you don't know how much has been shaved off the head or block, any machine shop can measure the height of them and compare that to the stock measurement, giving you the right number.

PS: Putting a MHG on an unfinished block and head is a dumb idea. Just sayin.

 

[radiod]

There's also a sticky at the top of the tech section here: http://www.supramania.com/forums/showthread.php?97552-Head-Gasket-thickness-selection

That should answer most of the questions you have. If you're not going to throwing a ton of boost at the build (eg. keeping it under 15psi on the CT-26 with maybe an upgraded wheel) then there is some room to up your compression ratio. I'm running 10-11psi (depends on the day) with my CR at 9.0:1 and I'm having absolutely no problems. Just for reference, stock is 8.4:1. I can't for the life of me find it right now but there are some threads/links about how to calculate your compression ratio based on the measurements of the cylinder/combustion chamber/piston/head gasket/etc.

Oh, and reiterating what Grim Jack said....don't put an metal HG on a stock machined block. Even from factory they don't necessarily come finished with the RA spec required for a metal HG. Do it right the first time and save yourself tearing everything apart again when (notice....WHEN, not if) it starts leaking on you.