whats the difference between...

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331 cobra

New Member
Oct 14, 2003
Silicon Valley CA
O-ring heads have four circular grooves milled in to the deck surface surrounding each cylinder. You have to use a special gasket that has o-rings in it.

The o-ring is a better seal if your cylinder pressures are very high, like supercharged, N2o or just bad detonation.

Unless you plan on boost or big shots of N2o, it's probably not needed and it just adds expense and possibly inconvienience when you pull your heads (special order gasket at most places).
If installed right IE the right gaskets and ARP studs. You will have no problems. O rings to me are a waste of time unless you are running serious boost (18-20psi) or tons of squeeze. I have always built motors with the fel pro 1011-1 or 1011-2 gasket and ARP studs and I have cracked pistons and blocks before the HG blew. Its all in the tune, the machine work and the install. Even though they tell you to install them dry, I always use Permatex Copper Spray on my gaskets, that stuff DOES make a difference and its works!! I detonated my 306 last year on 12psi so bad that it cracked my block in the #8 sleeve and took a chunk out of the piston, but the head gasket was fine.....