<VV> Mismatched Heads

Mark Durham 62vair at gmail.com
Tue May 3 11:59:47 EDT 2011


David, you should match the heads, one or the other. They are not that
expensive.

GM used the head design to establish compression by varying head
design, hence the CC volume and shape determines how the fule burns in
the chamber, and establishes the power of the engine. So you had more
power being produced on one bank than the other.

The engine cannot run as smooth as it should when in this condition,
and could this cause a crank to go bad? Who knows, but you are
introducing different rather than the same forces into the crank from
the power pulses, and could have been a contributer.
Mark Durham


On Mon, May 2, 2011 at 7:50 PM, David O'Neal <dnoneal at comcast.net> wrote:
> A while ago the crank broke in my 65 Monza 110 PG.  After tearing down the engine I found it had the appropriate 110hp head w/ chamber type "CC" on one side but it had a 95hp "FF" chambered head ('64 or '65) on the other.  The 95 SN is 3856743 & the 110 SN is 3883863 - I do have the tech guides.
>
> I think this is the original engine in the car, so the P.O. probably had a problem and got a junkyard replacement. BTY - The engine ran pretty well before the failure.
>
> So, is it critical that I get another 110 head instead of using the 95?  I don't want to spend big $$ on the motor right now.
>
> Could the mismatched heads have helped cause the broken crank?
>
> David O'Neal
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