Bingo! Some argue that running excessively high octane will actually decrease performance...think about it: high octane fuel is designed not to pre-ignite (detonation, knocking). The term I've seen is something about slowing/smoothing the propagation of the flame front so you don't have spontaneous combustion all over the combustion chamber. The optimal situation is running the lowest level of octane that burns smoothly...or the lowest level octane that doesn't cause the knock sensors/ECUs to dial back ignition timing. Turbos are a whole different ball game.

On the topic of octane boosters, the easiest booster is simply 10 to 20% straight toluene, which used to be about $5/gallon. Toluene is a component of gasoline anyway, so you're not adding in anything that doesn't belong. It has an octane rating of 114, and a 10% mix will raise 92 octane gas to about 94. For more on this stuff, check out http://www.elektro.com/~audi/toluene/

 

i used to run 93 on my 88 924S, then gas went past $2 and i just filled up with 87, no difference in performance. i fill up with 87 on the 85.5

 

oh and aren't those computer chips just bsing when they tell you to use 91+ octane? i upgraded the chip in the 924S and the car couldn't give a sh*t about what i put in there.

 

Crunky,

Don't be fooled! The stuff you are using gains a maximum of 10 "points," with a point being 0.1 - so at BEST, you go from 87 to 88, at the cost of $5. I am gussing you are using "Turbo 108"? It would be cheaper to fill with premium, plus it would be higher octane. You are spending more and getting less!

 

MAVFAN,

Those chips add power by advancing the ignition timing. With too much timing and too low octane, the car will do two things. #1, the power gain will not be present. #2, the car will ping and damage the pistons over time. On an N/A it's not that big of a deal, but if you hear it ping, you may want to either run a stock chip or use higher octane.

I had a chip for my car with the timing so far advanced, it needed 100 octane to stop the pinging. But the difference in power was VERY substantial.

If it was actually only $5/gal, I would run it more often. I used to run it all the time with one of my boosted cars, and it works wonders. I mixed a 30% ratio with 91 octane. However, you would be hard-pressed to find it for under $10-$14/gal. At least, that's the going rate that I've seen the past few years. Every once in a while I can score it for $8-$10/gal, but not often.

Once it gets that expensive, it's cheaper to buy VP 100 at the pump.

 

no pinging and no power gains no matter what octane. also its quite possible that the chip was a bunch of BS. i got it cheap from ebay.

 

I used to always fill up at the speedway with 91. Then we became CostCo members, and I found out that their gas prices there were $0.20/gal cheaper than anywhere else. Since then it's been 93, and loving it!

With my MPG spreadsheets, I've determined that the Porsche costs me $0.14/mile in fuel, while the Grand Prix costs me $0.11/mile in fuel. So, yea, I could same a few pennies/mile, but it would sure cut down on the grinnin', and that'd be a loss worth more than a few cents/mile.

 

lol. you could have saved yourself a TOn of money by having run 87 since you got the car.
9.5:1 compression doesn't need 91.

and to ppl who think they are losing a "couple ponies" by going lower octane. thats not true. a HIGHER octane can actually make you lose hp. not 91..but maybe like 100. the higher the octane just means its resistance to catching on fire. too much octane and the flame will start to late.(or take longer to burn or whatever)

 

actually...no you dont. that stuff doesnt work and any "increase in performance" is all in your head. lol

 

Sunoco has 94 octane here in Pittsburgh.

 

Exactly. You might "feel" some extra power, but its just a placebo effect.

Not neccesarily. If they're actually legit, they'll advance ignition timing and maybe spray in a little more fuel. The advanced timing might cause the engine to ping on lower octane fuels.

 

I've been running premium gasoline so far becaause I thought I had an injector problem, but my car now but no longer chatters. Regaurdless, I've heard that ethanol blended fuel is judged on a different scale than regular, so 89 ethanol, common around where I am and often much cheaper than other gasonline (10 to 15% ethanol blend) will typically have a shockingly low octane level- sometimes as low as 82. Or so the local gas station guy tells me, he even sells ethanol and hates it.

Running premium smoothed out the rough start ups, and stopped the rough idle problems I had...

I'll probably fill up with 87 next time anyway because I think my motor is pretty well cleaned out now Daily driving on premium gas for the last 4 months has improved the general running shape of the old girl. Or so I'd like to think.

 

ethanol by itself has a rather high octane rating, around 110 as I recall. If it isn't pinging, your octane is high enough.

 

electronic knock sensor means 89 is a-ok! I use 89 in both 944s, and even used 87 once with no real difference. Save money!

 

Ethanol has an octane rating on 116, methanol is 114.