My friend and I were debating octane today. His compression, i believe, is approximately 9.3:1 (crvtec, stock pistons) and my b18c1 motor is 10.0:1 stock obviously. I feel that running octane booster or whatever isn't going to make a difference...91 is just fine. I was under the impression that the higher the octane rating is...the more fuel can be compressed without igniting due to the compression (resulting in engine knock). He says it's more than that...that the fuel burns more efficiently and is more stable (i know it'll be more stable...but at higher compression ratios right?). Isn't 91 octane "stable" enough for our stock compression ratios?

Whatcha guys think?

-Rod


[Modified by RK, 10:13 PM 11/8/2002]

 

91 octane is perfectly fine for your current application. higher octanes are more resistant to pre-detonation and, yes, they do burn more completely and efficiently, raising your gas mileage and decreasing residual reactants in your cylenders. at 12.5: 1 CR you only need about 94-95 octane to ward off detonation, so keep that in mind when building your engines

 

Thanks for the reply

 

Hi octane has a slower burn rate so is prone to predetonation from hot spots in the chamber or piston(sharp edges).
An engine that needs 91 to run good will not run better (or make more power) with higher octane.
The only time an engine makes more power with higher octane is when the motor needs it
This has been proven on dynos and at the track time and time again

A little side note for people that live in cold climate winters:
Use 87 octane in the winter since the heat needed to ignite it is small,the higher the octane the hotter the spark has to be


[Modified by tk, 8:02 AM 11/9/2002]

 

Huh? I thought lower octane fuel was more prone to pre-detonation. Faster burn rate, no?

 

Higher octane doesn't always burn slower rate but ignite at higher temp.

 

With higher octane you can advance your timing more w/out pinging and get better throttle response. Also, with higher compression engines, the ECU can retard the timing if it senses knock, resulting in worse performance. But to answer the question, yes 91 is fine for most motors with stock timing.