Chris,
Although you addressed your note to "fellow Spitfire owners", I had some
experience with the 1500cc Spit engine in my 1976 Midget...
I ran a head shaved a full 100 mils with the earlier 9:1 flat-top
pistons. Compression was probably in the neighborhood of 11:1, judging from the
compression test (I never cc'd the head). I ran a stock UK-spec cam (non-smog)
because I just wanted a torquey, flexible engine and didn't really care about
maximizing top end. For this reason, I stuck with the US-spec single valve
springs (a mistake, in retrospect). I had the twin SU's pulled off an earlier
Spit, fitted with richer needles. I ran a glass-pack exhaust.
The engine ran very sweetly, and sounded just _wonderful_. There was no
valve/piston interference, but I stress that I built the engine for mid-range
performance, and I never exceeded 5000 RPM. If you're running one of the wilder
cams Kent offers, you would want to procede with caution, certainly using the
UK-spec dual valve springs.
BTW, I wouldn't endorse shaving that much metal off this head. The shape
of the combustion chambers was scary, and though I ground some of the sharpest
edges down to avoid heating them up like glow plugs, I never managed to cure the
car's tendency to Diesel after switching off the ignition. There was no
detonation or ping, however, even at high load/low RPM. I backed off the
ignition advance slightly, and obviously only used 93 octane fuel. Also,
clearance for twin SU's on a Spit manifold in a Midget requires creative
reshaping of the inner fender.
Hope that helps.
|