The owners manuel says we should run 92 octane gas or higher. Where I live 91 octane is as high as pump gas goes. Will 91 octane cause problems? If so, should I add octane boost from the local Autozone?

 

One time I was out of 92 octane and the gas station only had 91. It ran fine, with no pinging. It is only 1 octane point. I wouldn't worry about it too much, but if at all possible, run 92.

 

As you gain elevation octane requirments lessen. Are you at a higher elevation (above 4000')? One octane number lower using the Anti-Knock Index--which is Research Octane Number plus the Motor Octane Number divded by two(R+M/2) won't make much of a difference. The motor octane number provides a clearer and more accurate depiction of fuels anit-knock capabilities. More than 3 numbers lower(again R+M/2) in an otherwise stock application (read--not higher compression piston, head work so on) won't create any catastrophic problems.

 

I have a '00 400 and run 104 octane race gas. At first I ran Shell premium (I think it was 92 octane)which seemed fine except for some pinging under heavy load and difficulty starting and idelling when cold. I have never had these problems with the race gas. I am amazed at how easy it is to start. For example, after sitting six weeks in storage, it started on the first short press of the starter without even using the choke. I haven't heard a ping out of the engine since I switched. It can be hard to find race gas but if it is available I feel it is worth the extra cost. If you can't find the race gas you may want to try an octane boosting additive.

 

Right on about octane requirements diminishing with altitude, proven to me in my misspent youth crossing the Mexican cordillera while burning low-octane "Pemex" regular, the official (and ONLY!) gasoline availble deep in the interior.

I've wondered: Airplanes obviously need all the power they can get at low altitudes for take-offs and landings; thus, they use high-octane gas. However, at altitude, there's no way they can use the higher octane fuel to advantage. Wonder why they don't have "cruise" tanks, with lower octane stuff for altitude? If all piston-driven aircraft used this technique, lots of money and dinosaur juice would be saved.

Tree Farmer