Octane as it pertains to engine performance

[Edgeman]

Engine Masters had a naturally aspirated LS-3 on a Dyno at Westech, and decided to test 87 and 91 pump gas from a gas station down the street from them, as well as Sonoco race gas in 110 and 116 octane levels. There was no noticeable difference in power between any of the fuels. E85 did make a little more power across the entire curve. The first four fuels also liked the same timing...I think they said E85 liked a slightly different timing.

Bottom line: you aren't going to make more power by putting in higher octane fuel. You just need enough octane to prevent detonation. I've read that we may make less power running 87 because the knock sensors will detect detonation and retard timing, but you won't gain any addional power by going higher.

Now if you go boost...

 

[madtrucker]

I have heard the same thing. It's just all about ping.

 

[Click]

Yep, unless you have a high compression built motor or supercharger, you can run the lowest octane that won't ping. That's what I've always gone by.

 

[Gadget]

This is a great question. I wondered how the different octanes would work on my XRunner shortly after I got it. Still stock.

I was making a regular trip from Southern MD to a place in NJ. So great time to do octane MPG testing.

I always took the same route about the same time a day and got gas as the very same pumps.

Did a trip with 87, then a trip with 93. Then next was 87, then next 93 and so on. I think I made 8 trips overall.

This will blow your mind, I got a hair better MPG on 87. This difference really was not significant and I would say likely really no difference.

Wondered about power.. So I rented some dyno time. Could not do back to back dyno testing the same day because could not run the gas out. I think the dyno runs were three weeks apart. One done on 87. The next on 93. With a couple of tanks in between to make sure the gas was not mixed.

Ready for this???? The power was the same.

So, on an N/A stock XRunner, there is no reason to spend money on 93.

Bet you were not expecting that did ya?

 

[madtrucker]

I recently stuck higher compression pistons in my Harley. I had it dyno tuned, but it was pinging at low rpms, 2800-3200 rpms on 91 octane. We tweaked the tune to get out the ping. I didn't do anything scientific, but it didn't seem like mileage or performance differed. I know ping is bad for the motor. The X runs great on 91 with the TRD SC and stock flash. I would run the lowest octane that I could get away without ping.