Hey guys~

I was wondering if somebody could tell me how mileage is supposed to vary in relation to different grades of gas. I was under the impression that higher grade gas like 91 or 93 octane gas detonates at a higher temperature and consequently burns cleaner than say 89 octane gas. If this is true, does the higher grade gas also emit more "smog"? I'm following the reasoning that because it burns cleaner, more of it is turned into exhaust gases.
And also will a Ka24de 240 also get lower mileage using the higher grade gas (as opposed to the lower grade)? There are two gas stations near my house, one a Mobil, and one a Gulf right across the street from each other. When I fill up on "regular" unleaded (I believe it's 87 octane) at the Gulf, I get a few more miles in mileage than when I fill up the same amount of the same type of gas at Mobil. Does this make any sense?

 

Experiment.

If you drive the same amount of miles to work each day, get just enough gas to get you to work and back. Then calculate your MPG. Do it again the next day with different gas.

The short answer is that these cars are designed for 89 octane, so that's probably your best bet. Generally you get better gas mileage with lower octane, but you're risking detonation.

If you need more info than that, I can get you a link to several debates on an Accord forum.

 

well I was hoping somebody knowledgeable in engine tech might be able to give me a definitive scientific answer... I have experimented, and as I said in my post I get more mileage with the Mobil Gas as opposed to the Gulf gas~ despite the fact that they are both marked as the same grade (89 octane).

 

So you want me to post up some bull**** about linking chains of hydrocarbons together with 89 molecules of octane in them?

You want a scientist answer, ask a scientist. The basic answer, just like with most other stuff, is:

Every car is different. One car may run better on Shell, one on Mobil. One car likes Valvoline, another likes Royal Purple. It depends on the age of the engine and what you done to it, but on a stock engine that's made to run 89, 89 is gonna get you the best mileage.

If you're really worried about MPG, go advance your timing four degrees and run the highest octane pump gas you can get.

Oh, and about the "smog"- octane burns cleaner that other molecules in gasoline, so it leaves less residue or "smog". This is why you can run some fuel cleaner or octane booster for a tank and usually bring your N0X and other emissions down.

If you don't like my answers, that's cool, maybe it'll help somebody else.

 

anybody else have any other answers?