BBC closed chamber pistons and open chamber heads?

patman

patman

Club Member
I've got '71 ls6 closed camber pistons in my 454 and want to use 781 open chamber heads. I read that it can be done, but I want so experts to tell me if this is true. also if possible, can you tell me what the compression ratio might be.

thanks
 
1971 LS6 closed chamber pistons have .265" domes in a std bore, .221" in a .030", and .210" in a .060". With a open chamber head like a 781 or 049 it will work fine, although your compression will be 10.0:1 rather than mid to high 11's like a closed chamber head would yield. I'd go with it if it is what you have to work with already. As with any parts swap - test fit it. Check head to piston and piston to valve clearances first by setting the heads on the motor with no head gaskets and only a bolt or two to keep the head on and turning the motor over by hand.
 
Most closed chamber pistons will hit the head with open chamber heads.
Open chamber pistons will usually clear closed chamber heads.
I know this sounds backward, but it's true. It's due to the location of the
combustion chamber relative to the piston dome. Be SURE to check for piston
clearance to your heads. On a positive note, the -781 is one of the better oval
port factory heads.
 
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