Alan, also at higher altitudes, the available octane ratings drop because of
this effect, so you may still have to use the upper range. As I recall, in
Lubbock TX (~4000 ft) 90-91 was the highest octane you could get.
As a side note, at these higher elevatio, you should be able to get a bit
higher gas mileage (don't ask why, its somewhat complicated explanation).
As to the grade of gasoline, it was correctly pointed out that the minimum
tolerable octane rating can be adjusted by adjusting the timing. Retarding the
timing allows you to use cheaper gas at the loss of performance and higher
exhaust temperatures. Here is how I see it. An Imperial is not an economy
car. The gas cost will be high one way or another (since the initial cost of
these cars is small, I can live with high gas bills). Pre 72 Imperials were
also high performance machines. So, why compromise performance? Use the
highest octane gas, and advance the timing (assuming that you can hear and
recognize engine knock) at the highest tollerable level (usually higher than
the factory specs that were a bit conservative). This way you get the highest
performance and the coolest exhaust temperature (important if you are lead
footed and like to maximize the life of your unhardened exhaust valves). You
will also get a bit better fuel economy, but granted, the improvement will not
compensate the cost of the premioum gas.
D^2, 2x68s, one with timing at 11-12 B TDC, the other at over 20, both have non-
standard cams (w/ the standard cam, you may not be able to advance that much)
Quoting "ChiPieAlandPaula@xxxxxxx" <ChiPieAlandPaula@xxxxxxx>:
> Hello All,
> Just a quick note on the gasoline thread. An early issue of Special
> Interest
> Autos had an article regarding CR. They made the case that elevation
> above
> sea level is critical to an actual CR. Using their formula, my 64's 10:1
>
> ratio works out to roughly 8.8:1. All I can say is at 3500 feet, I can
> handily use midrange unleaded. I have no other independent research to
> verify
> this position. Do any members have knowledge of this?
>
>
>
> Allan From Montana
>
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