Dave,
unicorn7 wrote:
>
> Dee, I recently went through an engine rebuild with a '69 GT6+, and after
> careful consideration decided against the domed pistons due to both the CR
> problem, and the wealth of unknowns concerning the domed pistons (got flat
> tops for $275.00 + s&h). The recommendations I received amounted to this;
> the engine already has a 9.25:1 CR, and if that's not sufficient, there's
> enough information available in the competition preparation manual to get a
> flat top piston engine up over 12:1 if that's what you want, and none of it
> involves domed pistons. You can already anticipate a jump in CR after you
> have the block decked following cleaning and crack-checking, and the head
> should be cleaned up too (machined to ensure flat mating surfaces - improved
> sealing). Potential problems would include having to ensure there's no
> chance of an interference between pistons and valves, and the need for
> higher octane gas, expensive and not readily available to the general
> motoring public. If your intention is to drive it on the street regularly,
> or primarily, stay away from the dome.
Regardless of how it is achieved, (Domed pistons or Shaved head), 12:1
compression will always require the same octane rated fuel to prevent
pinging. The 10:1 compression engines normally require hi-test fuel but
sometimes operate ok on lower octane. The 12:1 definitely would require
higher octane fuel or octane boosters.
After my own problems with shaved head and high compression (that's a
long story) I would opt for the piston route rather than dramatic head
modifications, with the expectation that the manufacturer of the pistons
had enough sense to make sure that their design is proper for the
particular engine. But that is a matter of research into the
manufacturer's quality.
Regards,
Joe Curry
--
"If you can't excel with talent, triumph with effort."
-- Dave Weinbaum in National Enquirer
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