dbspcl

If your tuner couldn't get any more performance out of higher octane gas, then you need a new tuner (I'm assuming he was actually tuning the car, not just running dyno slips). The higher octane provides you the ability to advance the timing more without knocking, and that will always give you better performance.

dbspcl

I'm not understanding your point. Clearly it makes a difference - let's see 2 @ 87 and 14 @ 91 works out to an average of 90.5. If your car is tuned for 91, you're only at 90.5, and it will therefore knock/ping, which will damage your engine. Now if you want to average things out, put 93 in and run your 91 tune until the fill, then put 91 in. 2 @ 87and 14 @ 93 works out to 92.25.

GT Bob

OK guys...seriously... If our cars were THAT sensitive to octaine that they would blow up inside of a week. I am so sick of hearing that you need to run 1 ,2 , 3 tanks of gas thru your car, get an old priest and a young priest to bless and exorcise the car of the lower octaine gas and have a Buddhist monk purify the spirit of the gas tank before switching tune...

let me kill this stupid damn myth now...

couple of things to think about:
1. Our cars have knock sensors. In fact, I would say our cars have one of the best knock sensors setup and strategies I have ever ever tuned. It can DEFINATELY compensate for a gallon or so of lower grade gas.

2. Ever get stuck somewhere and have to fill up at one of the economy stations? Think their gasoline is the same quality as the others? Or perhaps they got some water in the tank, or Sparky the truck driver got confused and put 100 gallons of 87 into the 93 tank (and yes, this happens alot more than you would care to believe)? If our cars were as sensitive as you seem to say, then about 2/3's of us on this board would be on our third or fourth motors..

3. Did the person in line before you fill up 91/93 also? If not, then about the first half a gallon (give or take on pump setup) of fuel your getting, is whatever they bought.

4. Hot outside? Engines are much more prone to detonation in hotter weather, which means all that timing you have thrown at the car would pop the motor faster than you can say "bye bye motor."


Am I saying to go out and run a tune with alot of timing on 87 octaine? No. But use some common sense here people. Run your tank as low as you dare (somewhere between a 1/4 tank and the fuel light coming on), fill up with the better grade fuel and flash away.The knock sensors can handle a pretty wide array of conditions and will more than keep you safe while that last little bit of low grade gas runs out.

Mishri

^ +1.. Ive also been told by refinery workers that gas fairly quickly loses octane as it sits.. its possible that 93 or 91 you filled up with has sat for nearly a month in transport or in tanks and is now actually 91 or 89.. 1/2an octane doesn't matter(or even 1).. and that is why octane booster is a joke..

Gene K

Run it down until the low fuel light comes on (2 gal) and then add 4 gal of 93.
And run it down until the light comes on again and fill up with 93 octane.
That will give you around 92.75 octane.

Alternatively run it down until the low fuel light comes on and fill up with 93 + Lucas Octane Booster. Its been tested in independent tests to be one of the most effective octane boosters on the market although their some question of its long-term effect on CATs (100,000+ mi) of its primary ingredient (MMT) if used continously.