Thread: 93 vs 91 Octane - Beck Racing Engines Chevy 496

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Thank you for your help!

Welcome to CHR! Not only is your octane level dropping three points you're losing air density with the dry, desert heat, too! You might have to drop your total timing back a few degrees, but I'd probably wait and see if I got any WOT ping/clatter.

so i am thinking you should talk to beck racing engine see what they would say . I know what McCarthy Performance would say

A lot is going to depend on where in AZ you end up at. Tucson is about 2600 ft and Phoenix is around 1100 ft. Where I'm at (down south) we're at 4500 ft.

As Roger points out, air density makes a difference, especially on carbureted engines. The higher the altitude, the less dense the air and in effect the less your dynamic compression ratio letting you get by with a bit less octane.

Coming from sea level and depending on where you end up at chances are you end up dropping a couple of jet sizes and on lower compression engines they tend to like a bit more timing.

The big thing you will want to do is make sure your cooling system is up to snuff as summer can be a real challenge.

A bit more news you probably don't want to hear, besides only finding 91 octane, it's also all 10% ethanol. In the summer at altitude the ethanol fuel tends to be more susceptible heat soak and vapor lock (both of which can be overcome but usually it takes a little work).

Welcome to the board and AZ.


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