Chris, I agree with your comments on the avgas reducing pinging and
detonation, but not on the other two issues.
As mentioned earlier by another respondent, Tetraethyl Lead was added
to gasoline originally to increase its octane rating. There is a
frightening story about the fellow that introduced TEL in the 1920s.
As a demonstration, he would gather a crowd of people around his
Model T and advance his timing with the lever on the steering wheel
until the engine was pinging. He would then take a little bottle of
TEL and sprinkle a couple of drops on his NECKTIE!! He would wave
the necktie near the air intake of the engine and presto! The pinging
would stop. You wonder how long he lived, or whether he went mad
from lead poisoning. The lubricating effect on the valves was an
unexpected benefit.
As for the change in overall mixture at altitude, I have to disagree
also. Air (actually oxygen) is going to be LESS dense at altitude.
A carburetor works on Bernoullis principle, which depends on the
speed of the air through a venturi, not its density. Therefore at
altitude at any given throttle setting, the airstream in the carb will
be pulling the same volume of fuel into the venturi as it would at
sea level. But since there is a lower density of oxygen molecules at
altitude, the overall mixture will be richer, not leaner as you
mentioned. Thats why SU specified an alternative lean needle for
MGBs if they were sold in places like Denver or Tibet (Did any get
sold in Tibet?).
Cheers, Paul Kile, Fair Oaks, CA (62 MGA, 74 B-GT V-8)
an alternative lean
Paul D. Kile
kile_paul@aphub.aerojetpd.com
(916) 355-5162
GenCorp Aerojet
POB 13222
Dept 5784 Building 20019
Sacramento, California 95813-6000
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