All I can find here in Tucson is 91 octane. That's all I use but am I missing out by not using 93? There's racing fuel here, but like said in other threads, it's not gonna help me if I don't have high enoughof a compression ratio.

 

Your not missing anything by running the 91. Worst case is that the knock senosors will pull a few degrees of timing out if it knocks, but you are not really losing any power.

 

After driving cross country many times, I noted that the octane number for each grade of gasoline drops thealtitude above sea level rises. Probably becauseas the altitude increases the chance of knock decreases. So premium fuel which is labeled 93 octane near sea level (94 octane for Sunoco super premium on the East coast), in high altitude locations, like in the Rocky Mountains, premium fuel is labeled91 octane.

 

Hm, ok. Thanks!

 

Really? I've heard that cars run better the closer they are to sea level. If that's true, why?

 

At sea level the air is denser and allows the engine to make more power. The denser air allows the engine burn more fuel properly and thatgenerates more power.

 

The high altitude helps with pinging issues, but since the cars aren't made specially for high altitude places (Henry Ford actually made special "Denver heads" for some cars that were for high altitude, but that doesn't happen anymore). Needless to say, the minimal advance in timing cars can get up here nowhere near makes up for the less oxygen. Check out the NHRA website, they have corrected figures for major tracks that they run on so you can get your corrected time if you run at a higher track (take me for instance, in Denver I run a 14.7, at sea level with NHRA's figures I'd run a 13.8).

 

Oh, ok. That makes sense. Thanks for all the help guys!