Hi, Andy.
On this business of pushing compression to get more ooomph, I'll toss
my $0.02 into the ring(*). My Spitfire has the 1976 9.5:1 compression
ratio instead of the more common 7.0:1, and when it was rebuilt last
year, we kept that "feature". It's gas spec originally called for 95
octane (yeah, right!) but the best I can get now is Sunoco Ultra at 94,
and sometimes I wonder if there is any difference between that any other
gas except the macho price. This engine has always pinged a little under
full throttle, maybe worse now. (Actually, the engine in the Naugahyde
Duck, a 1979 Chevy van the band uses, is quite picky about 87 vs. 89.)
I've 'sperimented with retarding the timing until the pinging stopped,
but that also kills a lot of the throttle response. It has always had
a slight leak in the vacuum retard unit. Since this functions at idle
only, I pulled the vacuum line and plugged it just before we left for
the mountains this weekend. I figured the extra air might be leaning
it out enough to contribute to the pinging. I don't know if that helped.
To make matters cloudier, it isn't easy to find Ultra in Bartlett, N.H.,
so I had to put in some 92 then some 93. Needless to say, it is less
happy now than it was last week.
I am still undecided on how to set the timing (besides which, any change
in the timing also affects the idle speed, which if it is high enough,
also further affects the timing so I have to iterate in to a solution,
and I still haven't reduced the idle speed yet so it now idles at 1800).
V-B claims to have the vacuum retard unit, so I have one on order, just
to make it easier to pass emissions testing next year. When it arrives,
I'll have to go through the whole timing thing all over again.
In summary, I'd have to say it's nice to have more power but it's also a
hassle to have to look for, and pay for, the fancy gas. O'course, I "get
by" with a Spitfire so my outlook may be different from yours with your
TR-6, but I'd suggest the extra power might be more trouble than its worth
for you. There are times when I've second-guessed my decision to build
another high-compression engine (until I slingshot it past a truck, then
I'm glad I did).
* - Courtesy of your local chapter of the Mixed Metaphor Foundation. You're
just gonna' have to take the bull by the horns of a dilemma and face the
musical chairs. I never metaphor I didn't like. Except for metaphysics.
Speaking of physics, I flunked a test on gravity last week, and ever since
then I've had a real problem with a tendency to float aw a a y ...
Jim Muller
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