OK geniuses, here's the question: Does anyone know if there is any noticeable (measurable) MPG difference in the S (mine is an AP2) with 91 octane California premo compared to the 93 octane available in most other states. I know that the energy in a gallon of gas is not determined by octane, but I'm wondering if a slight ignition retard prompted by the knock sensor may, ever so slightly, degrade fuel economy with the 91 octane when compared to a slightly more advanced ignition with the 93 octane gas. I know that no two cars can ever be driven exactly the same and the same is true for the same car under different conditions, but has anyone ever had the opportunity to measure MPG in your S using both types of fuel and detected a difference?

Thank you

 

i would guesstimate that the difference would be negligible. maybe a very slight decrease in mpg/performance (after all, pulling timing isn't what you'd want). but it's not as bad as going from 91 to 89 or even worse, 87 octane.

 

There will be zero difference in performance of any gas grade beyond 91 without fuel and/or timing tuning. Honda tunes it's cars in the US for the lowest grade premium gas. This is 91 octane. The car should not ever knock in it's stock configuration. Extra octane won't help.

 

[QUOTE=CrazyPhuD,Aug 16 2005, 11:53 PM] There will be zero difference in performance of any gas grade beyond 91 without fuel and/or timing tuning.

 

unfortunately in this case 1-2HP gain is a statistically insignificant result. You're talking about ~1% of whp. Being extremely charitable and taking the G-tech at it's word for it's accuracy, it is only good for HP and TQ accuracy of +/-1%. Since 2HP falls within 1% of rated wheel HP you are within the tolerances and accuracy of the equipment. As a result the only conclusion that you can draw from these results is that they are statistically equivalent to each other. You can't really say that one is more or less powerful than the other.

As for MPG, it is possible that higher octane can result in worse MPG. Why? Higher octane fuel is more stable and actually more difficult to ignite(hence why it resists detonation better). It is possible that you are seeing incomplete combustion with higher octane fuel which can lower fuel economy.

 

Stock ECU will advance the timing for up to 94 octane.

 

actually, S2000's have shown gain/improvement in horsepower when using race gas such as 104 octane. Ultimate Lurker has indicated this on several occasions. Even on a nice cool autumn day, with 93 octane in the tank, our car will still pull some timing. Our knock sensors are paranoid. Higher octane gas does actually benefit the S2000 from the tests that have been done.

 

I believe dyno's of S2000's on regular vs race gas showed in the area of 5whp gains.

 

the ECU doesn't advance timing per se. what it does is NOT RETARD timing as you increase the octane of fuel you put into the tank. higher octane means less ping/knock, which means less pulled timing.

 

OK guys, I don't get it. If there are slight horsepower gains with higher octane fuel (to a point), why doesn't this translate into slightly better MPG for the same kind of driving. Won't less throttle producing the same horsepower save a little fuel by propelling you at the same speed over the same distance? Could it be that higher octane, above nominal, only allow the motor to make more HP at top RPMs by fully advancing the timing (or, no retard timing if you prefer say it that way). Why would you expect poorer MPG at, say, 65MPH in 6th gear, where there is no need to retard timing with either 91 or 93 octane. Shouldn't the MPGs be identical with the two fuels? Thank you