Driving to Colorado from Ohio: Octane Issues?

[JackMan]

Hi all

I plan to drive from Ohio to Colorado. My car is an 89 with 10.3:1 pistons, valve and cam work, SW chip for 91 octane, etc.

Will I have a problem running the car in Denver? Anything I can do to alleviate or protect from detonation?

I ask because I understand Colorado fuel s++ks.

Any advice?

Wellborn

[Matt Monson]

For starters, we have 91 octane all over the place here. Beyond that, our elevation is like gaining octane points, not losing it. So, functionally 91 octane is like 93 octane. I don't know who told you our gas stinks but maybe they ignorantly thought that because we have 87 as standard instead of the 89 you find everywhere else.

Not only is there the added knock resistance provided by the altitude and different oxygen content of our air but 90% of the general population has somehow gotten it into their heads that octane knock ratings are somehow an indication of gas quality. They are not. 85 octane gas is not of lower quality than 91 octane. It's just lower octane. Generally higher octane fuels, or "premium" as they call it have more detergents and additives in them but that still doesn't make them better.

Up here I run my 10.5:1 CR Subaru 2.5RS engine on 87 octane all day long. No detonation and perfect A/F's. Puts out 225chp from an engine that was rated at 165chp from the factory. Of course, more than just the pistons were changed.

Given the cylinder head design on your 911 which is a bit more detonation prone than a Subaru, I would say your best bet is to just stick with our 91 octane. It will be like running 93 octane but the next step down won't give you enough restance to detonation especially with the 90-100 degree days we've been seeing recently.

[fintstone]

Do expect a quite a bit less power at altitude though.

[fbarrett]

Wellborn:

What Matt said.

Your mixture will richen as you climb in altitude (same gasoline density, lower air density), and the likelihood of detonation will decrease. I had a 300SEL 6.3 once, and whenever I drove it to low altitudes, I had to either stay out of the throttle, fiddle with the timing, or take along some of that lead additive to control detonation.

Yesterday I drove my old Alfa (dual Webers, electronic ignition) to 12,000 ft for a plug check, and it was fine. Make sure your ignition system is providing a good spark. No complaints about the gasoline here--it's the thin air that causes the descrease in power.

Frank
'65 912

[tcar]

Heard that you lose about 4% per 1000 feet gain in altitude.

It's relative, though, everyone else is using thinner air (except the turbo guys), so you'll have the same power relative to everyone else.

Our gas is fine - don't know where you heard that it sucks.

[JackMan]

Wow, thanks for clearing up that really big misnomer. Colorado here I come. I'll post pixs and trip thread when I hit the road.

wj