<VV> low octane gas accident

Padgett pp2 at 6007.us
Fri Oct 21 11:32:37 EDT 2005

>It didn't knock and ping on the way home but I'm a little concerned.

Lot depends on how you drive. To my way of thinking, only the 140 and 180 
should require premium. OTOH, for a lot of cars in the 1960s, 9:1 
compression was high. I have not run any studies on the detonation 
characteristics of modern gas, just know that our modern cars (and one has 
10.5:1 and is designed to run on 87).

A lot depends on the size and shape of the combustion chamber and the 
location of the spark plug (spherical chamber with the spark in the center 
is best. You want to minimize the distance the frame front has to travel 
and reflections are bad. This is why engines have a similar displacement as 
in the 60s but are undersquare (longer stroke than bore) rather than 
oversquare as was popular back then. For a given displacement, as the bore 
goes up, so does the octane requirement.

An air cooled engine is liable to need more octane than a water pumper 
because the chamber temperatures are hotter.

All of that said, every engine is different. *In Theory* a Corvair 110 in 
good condition should have no problem running on 87 with the timing 
adjusted for the faster burning fuel. Considering that my Corvair is not 
intended to be a daily driver, I put 93 in it and just take the 10% hit.


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