Octane Questions

[surflvr911sc]

Here in CA the highest octane rating I can find anymore is 91. What do you all think of octane booster additives? The only additive I’ve ever put in my car is an injector cleaner on occasion, I even hesitant about those. Does anyone have any experience and data on the use of octane boosters? Are there any timing issues when running higher octane? Does anyone know a place in Southern CA that sells higher-octane fuel? Should I just not worry about it and run 91? Any thoughts or advice appreciated.

[RarlyL8]

Your '81SC shouldn't need more than 89 octane at best. You're fine.

[ronb]

will it run better on a higher octane though? ie 93 or 94 instead of 89?

[Rot 911]

Originally posted by ronb
will it run better on a higher octane though? ie 93 or 94 instead of 89?

No. The only reason you would need a higher octane in a stock SC would be if you had so much carbon built up on the pistons that it was increasing your compression ratio. If that was the case you would be hearing detonation upon accelleration.

[surflvr911sc]

I do have a ping under load I can't quite track down. Could this be timing, clogged injector or carbon build-up causing high compression? The valves were just adjusted so I know their OK and the ping was there before that was done. I know Pings are bad, what would the most likely cause be?

[scedmonds]

If your engine pings at high rev's, it may be that the timing needs adjusting. That did the trick with my '83.

91 octane should do you fine, though Unocal 76 sells Competition 100 (100 octane) racing fuel in selected SoCal outlets . . . some folks have had success with blending this fuel with 91 octane.

Check www.76.com . . . there's nothing close to San Diego, here, but stations in Newport Beach and Ontario are listed.

Cheers!

C.

[cegerer]

Rarly's got it right. 89 is all you need. It's tempting to run high octane fuel in a high-performance car like a 911 because that's what high-octane fuel is made for. Isn't it? Actually it has everything to do with compression ratio and NOTHING to do with how fast, or what kind, your car is. High octane fuel is less volatile than low-octane and may not even burn correctly in your car. If it's any comfort, always remember that the legendary 73 Carrera RS runs on cheap 87 octane unleaded. -- Curt

[CEO]

http://www.cmhnet.org/~charlie/photos/cars/audi/toluene.html

Works pretty good, though i recommend Xylene as it is better because of the evaporation and burn rate characteristics. You can buy a gallon for ~$7.00 at any Sherwin Williams. W/ a 3:1 ratio of xylene (25%) and using 93 octane you have about 98-99 octane unleaded fuel.

I've used it extensively in a 10sec buick TA before. Also the xylene won't hurt O2's, it actually cleans them along with the intake from gum and tar, and it also commonly used in fuel injector cleaner.

[bob hodges]

Using Octane booster has a long term effect on the ejectorsand the spray pattern You will notice that the spray pattern is effected by the booster. Don't believe the SC will be needing any booster.

[bornrich]

I posted a simlar thread a few weeks ago. My 81 SC pings under acceleration on hot days running 91. My mechanic says it is timed to spec and the only thing I can do is retard the timing or mix gas. I don't want to affect the perforamce too much by retarding the timing so I mix with 100 Octane once in a while.
I wouldn't dare run my SC on anything less then 91 for fear of the pinging becoming an everyday thing.