Octane Difference

[LedZepplin77]

I bought a tuner/CAI kit from RPMoutlet a while back with 3 tunes, 87, 91, and 93. For now, I've only really used the 87 tune. If I bumped up to 91 or 93 do you think I would see any real gains, and Speedways only have 92 octane gas. Would it harm my engine at all to run a 91 or 93 octane tune on 92 octane gas? Thanks guys.

[Deimos]

You would want to run the 91 tune for the 92 gas. The rule is to always use the tune for lower octane than what you have in the tank. That way you can avoid detonation.

You might feel a slight performance increase in the higher octane tune but it's hard to say with canned tunes from SCT. Your best bet is to get in touch with a professional tuner such as Brenspeed or Bamachips. They sell individual tune files for your SCT in whatever octane you want. Their tunes are typically better than what you get stock from SCT. Bamachips tune files start at $50 each.

[Nice Pony]

I run the 93 Octane Performance Plus tune from Doug at Bama Chips with my X-Charger with a 2.8" pulley all the time on 92 octane gas. Doug told me it would be perfectly safe in a moderate climate zone like the Pacific Northwest but he also said not to run it that way in a hot dry climate area.

Theoretically you get more power with a higher octane tune because it allows for more timing advance in the tune.

[LedZepplin77]

Ok, cool, thanks guys, one more question, do you think I'd see any change in my gas mileage? I was just thinking the other day, 93 octane fuel has MORE chains of carbon per gallon right? So therefore if anything, my mpg's should go up a little or at the very worst just stay the same? A performance tune should be just getting the maximum efficiency per gallon of gas as well? So theoretically a good performance tune from Bamachips should raise my mpg slightly possibly? (Plus some mo powah)

[48prerunner]

There is a big write up somewhere i remember reading about 93 vs 87 and the cost and increase in mpg but dont remember where sorry think it was in FAQ on some forum, but I think it pretty much evened out.

Fuel and Octane

A vehicle's fuel economy depends on the energy content of the fuel on which it runs. This has been determined by EPA and others and is consistent with combustion theory. Ethanol blended fuel may decrease mpg by about 2%. MTBE (Methyl Tertiary-Butyl Ether) oxygenated fuels reduces mpg by about 2-3% because they contain less energy than non-oxygenated gasoline. In addition, the energy content of gasoline varies from season to season. Typical summer conventional gasoline contains about 1.7% more energy than typical winter conventional gasoline.

Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders.

Most gas stations offer three octane grades: regular (usually 87-octane), mid-grade (usually 89-octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

Stock PT's should use 87-octane fuel for optimum mpg. PT's with a supercharger or turbocharger should use 92-octane. Expensive high-octane gasoline (premium) does not give your car more power or better mpg. According to the AAA premium gasoline sells for an average of 17 cents more per gallon than regular gas. Only about 6% of cars sold in the U.S. need premium gas. Still, premium gas accounts for 20 percent of all gas sold. Resist the urge to buy higher-octane gas for "premium" performance.

The only reason to use high-octane gasoline is if your car knocks or pings on your normal grade of gasoline, and your mechanic has been unable to find any other easily fixable cause. The PT uses a "knock sensor", which detects knocking and protects the engine by retarding the ignition timing, however it can't compensate for a severe malfunction, a condition which can affect engine performance, fuel economy, or even damage the engine

[roddy]

If you have the ability to remove a couple of degrees of timing, then I suggest you do it before trying the 93 tune with 92 gas. (depending on the tune, a slight difference in timing may be the only difference between a 91 and 93 tune, anyway.)