Octane revelation

[chas]

locally, in the metro area, we have a rather high ethanol content in the gas to reduce smog--i.e. oxygenated gas. this is particularly true during the winter months. i due notice a bit of a drop in mpg during this time (about 2-3 mpg on the average). about 2 years ago, i am fairly sure that they started adding some ethanol to the gas year round. i lost about 1-2 mpg at that time.

on trips north, like pa, gas from local filling stations provide better mileage (not just due to highway driving) and power.

do you need higher octane? check exhaust gas temps would be one way to check, you could also check the knock retard on your engine (you would need a obd-ii scanner). if you have a fair bit of knock retard, you should raise your octane.

slower burning (93 octane) also means less power (if you could be running 87 octane).

[zlexiss]

I think Chas hit on something - I bet smog and other regulations can mean on a lot on which prem gas you get. High smog urban areas will probably always see oxygenated gas for octane boost, and if you go outside the metro areas you have a better chance of getting the good stuff. Depending on the supply chain of course.

[chas]

i dont know how oxygenation is going to affect the octane. i know that it reduces the amount of fuel that my car gets to burn. less fuel = less power.

[Seppo Kaitainen]

If you flogg you car on a daily basis run 93. Otherwise 87/89 is fine, and only run 93 if you are planning on flogging you car during the next tank.

I was faster in the 1/4 with 93. Most likely because I was seeing some Knock retard with 87.