Higher Octane or Race Gas anyone?

Doug Franklin

Registered User
Just wondered about any experience with higher octane than 93 in SC stock or modified? I have it available close by.
 
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I'll usually mix some 110 octane in when I go to the track. I keep my WOT timing at about 28 usually but when I mix in half and half with 110 octane I bump up the timing to 30 BTDC @ WOT and pick up a couple of tenths in the 1/4.
 
I've ran 104 in my stock '93, and it really wasn't worth it.
I felt just a tad bit more pull at 3500+ RPMs and full throttle, but when it's under 10psi you won't notice it. I assume it'd work better if I had a pulley and cranked up a bit more boost.
 
I would run 93. Before I tuned my car with the EEC tuner, I was having issues with detonation due to having removed the EGR. I was running a stock blower with a 10% pulley getting about 13 psi. I found that changing to Autolite 103 plugs gapped at .045" cured that detonation.

Then I went to an EEC tuner and started to increase timing. I found I got more power running up to 30 deg total timing. 31 degrees will detonate even with the colder plugs. On the advice of Brian H and a number of other people who have experience in this I backed the timing down to 28 degrees for pump gas but the car slowed down noticably at the track.

With the car at 31 degrees I noticed that the car was detonating again, and the addition of a 25-40% mixture of 107 octane stopped it but the car really wasn't any faster. Currently I run 26 at torque peak and 30 degrees at hp peak. I am running about 15psi on a 5% OD and it seems ok ( I run stock pistons etc). However, others who are running the stock spark plugs would disagree.

I believe that one of us was running up to 33 degrees with race fuel but it resulted in a melted piston. I don't think that race fuel really allows for that much more timing that it warrants it's use.

I think that spark plug selection is crucial to avoiding detonation in a competition motor. The 103's that I run are short tip and colder heat range than stock. It made a noticable difference in my car.

I guess my point is that we don't really run enough boost to warrant race fuel with the tune that the EEC has, and to retune the EEC to benefit from the race fuel significantly is not really worth it. People who have tried alcohol injection have had similar results.

Another thing to think about is that race fuel has different burning characteristics which results in a different a/f ratio. With the adaptive nature of the EEC, if you switch back and forth between the two you could end up running really lean at one point. Not sure if anyone really knows how long it takes the EEC to learn a new mixture. Not a nice thought IMO.
 
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