Lee,
I live in Broomfield, CO, and have a 9.5:1 compression TR6. I haven't
tried it on pure low octane yet, but I think that it would run ok on
it. I've been mixing fuel lately, that is, one fillup I use Premium,
the next I use the regular stuff. This seems to be working just fine.
I have a mild cam in the car, and I would suggest that you not mess with
your cam unless you have to. If you do, you might want to increase the
lift, and not mess with the duration too much. There is a place in
Denver (Zimmer Automotive) that has several grinds for the TR6. The
grind will cost you $45, and I can help recommend one if you want to go
this way. The stock TR6 cam really is short wrt lift. I would check
your lifters with the head off. If they all look fine, then don't mess
with the cam. If the cam is out of the car, go for a mild grind and new
lifters.
As for how much to shave off the head, I would go to 9.0:1 compression.
I think you would be as happy with that as I am with my 9.5:1. You want
to go as high as possible for a couple of reasons. The main one is
altitude. At the higher altitudes, compression in your engine is
significantly lower. 20% at mile-high to be exact. It's no wonder our
cars seem a bit doggy up here.
For a 9:1 compression ration you'll want your total head thickness to be
about 3.42 or 3.43. You can decide on what you want from the values
below, which have been taken from the TR6 competition prep manual
Head Thickness Compression Value Notes
-------------- ----------------- -----
3.550 7.5 Stock for Late TR6
3.460 8.5 Stock for 69-71 TR6
3.4 9.5 Approximate value
3.375 10.0
3.295 12.0
Anyway, hope this helps. Good luck with your modifications. Let me
know if you have any other questions, as I went through this just last
spring. BTW, my car passed emissions with flying colors.
Cheers,
-Scotty
'75 TR6
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