[DML] Re: Premium Gasoline

[William T Wilson <fluffy@xxxx>]

On Tue, 31 Aug 1999, Ann & Ed Thompson wrote:

> I guess I wasn't thinking about the folks that live in the clouds on
> purpose where real gasoline isn't readily available. If Erik does
> live in or near the high mountains of Colorado he can go to a good
> speed shop and get an octane booster.

It's actually okay. In the high altitude of Colorado (Utah, Nevada,
Wyoming, etc.) naturally aspirated engines require lower octane rating. 
The conventional wisdom is that high altitude adds 2 points to the octane
rating, which is why you see 85/87/91 grades rather than 87/89/93 like you
do in the rest of the country.

Octane booster is almost totally worthless. About the only thing it does
is foul your spark plugs. If it worked as well as they claim racers would
just use that instead of paying $4/gallon for real race gas.

The only reason octane booster people don't get sued more often for false
advertising is that they say "boosts up to seven points" or whatever. In
fact, when mixed with premium gas, the effect is at most 1 point of octane
incrase. It works great when you mix it with 85 octane gas, though - but
then why bother? :}

> That's not a problem. Actually that would be even a better test for
> troubleshooting the pinging if it is pre-ignition. He could boost the

Unless the timing is grossly advanced (which would be easier to check and
return more definitive results with a timing light) there is no set of
circumstances that I can think of that would cause detonation at light or
idle load on a stock DeLorean. A little detonation is normal going up a
steep hill or at full acceleration in many engines (of that vintage -
modern engines should almost never detonate), but not under cruising
conditions. An exhaust leak, on the other hand, will be audible under a
wide range of circumstances.

> knock detection device (except for the driver's ear). The DeLorean is
> supposed to run fine on regular grade fuel but I have always used
> premium grades in mine.

That's reasonable enough. The higher grade fuels typically have better
additives and are more 'pure' than low grade gas. But the DeLorean has a
very low compression engine which should run fine on just about any fuel
grade. As long as you don't have detonation, additional octane, per se,
is wasted.

> It occurred to me that if Erik does have a pre-ignition problem it
> could be that the engine was tuned for one altitude and was later
> moved to a significantly different altitude without properly tuning
> the engine for the new altitude.

I don't think this would make a lot of difference. The difference in
octane rating and the difference in air pressure typically cancel each
other out (on a naturally aspirated engine).