Better Mileage or slate of hand?



My local mechanic said I can get better mileage in my 2002 Honda Accord (v-6) if I use premium gas and “If I advance the timing until they knock and then back up a few degrees. It only takes a few degrees to improve mileage. More efficient burn means more power from the same fuel which translates to better mileage.” I don’t know a knock from a knockwust. He says he does this all he time on most of the cars he has owned, even able to get 20mpg with a full size Cadillac with a 500 cubic inch engine and over 20mpg with a 455 cubic inch Tran Am. So will this proceedure give me better MILEAGE (I’m not looking for better performance) on my computer controlled vehicle, or will I just be wasting money??? Thanks experts!


Your first step is finding another mechanic.

In the old days one could improve things a bit by advancing the timing a few degrees.
Newer vehicles run much hotter and leaner (meaning a skimpier relation of fuel to air ratio) and what your mechanic is failing to tell you is that advancing the timing too much can destroy an engine.

This will usually happen during extended driving at highway speeds.

Maybe you should ask this mechanic if he is willing to stand behind any engine damage that may be caused by this - in writing of course.


[b]Well first off, find a new mechanic.

Second, the ignition timing on your vehicle cannot be adjusted. As it’s controlled by the computer.

Third. a higher octane fuel will not gain better gas mileage. As a matter of fact, using a higher octane fuel in an engine that doesn’t require it can result in poorer fuel economy. As a higher octane fuel is harder to ignite. And using a higher octane fuel can also lead to carbon deposits in the engine.

Just follow the owners manual for fuel recommendations. Afterall, the Honda engineers did all the research to determine what’s best for your vehicle to obtain the highest fuel mileage.



So, your mechanic knows more about fuel mileage and efficiency than the engineers at Honda, eh? He missed his calling. He could be SUPER RICH, and yet, there he is, living the simple life of a humble, shade tree mechanic. What a guy!

I have a suggestion: NEVER go near this fellow again, for any reason whatsoever.


I agree with everyone else so far about the timing. It’s a bad idea, even if it were possible.

As for the gas, I have a slightly different take. I owned a 2000 Honda Civic LX for seven years, and drove it 155,000 miles out of it’s current 180,000 miles. I recently sold it and bought a 2007 Civic Hybrid. In each of these cars, the recommended fuel is the standard 87 octane unleaded. At about 20,000 miles, I started using 89 octane in the 2000 Civic LX. What I found was that in the summer I averaged about 3 to 5 mpg more with the 89 octane. With all the crap they put in the gas in the northern states during the winter, I didn’t see any gains there. The car also accelerated better and ran smoother on the 89 octane, compared to the 87 octane. I never ran Premium in the car, as I was told by a mechanic at Honda that Premium burns too hot and it could damage the small 110hp alumnimum 4 cylinder engine in the Civic LX. The car now has 180,000 miles on it, and my brother drives it 150 miles a day for work… and it hasn’t had a single engine problem yet.


I cannot for the life of me imagine any reputable certified mechanic making this recommendation on any modern engine. Unless this comment has been extracted from a much longer and purely theoretical conversation and is thus out of context, I wholeheartedly concur that a new mechanic must be found. This shows a serious lack on knowledge of modern systems.


Your mechanic can not adjust the spark timing. That is determined in modern cars, meaning from the 1990s and later, by the knock sensor(s) on the engine block. The computer will advance the spark timing until it gets a signal from the knock sensor. The knock sensor is sensitive to sound.

If your mechanic were to charge you money for this modification, he would do nothing, advise you to use premium gasoline, take the money and scam yet another person; see as follows:

From what I have found on the Internet, there are modern engines designed for 87 octane fuel that will advance the spark timing as permissible with octane higher than 87 to increase power and mileage.

You may have a smart mechanic that you might want to keep available but you must use a little effort to keep him honest.

Try a higher octane gasoline to see if it works for your car. The test conditions must be identical.


“More efficient burn means more power from the same fuel which translates to better mileage”

No, im not so sure it does, if your car is running rich, some of your gas will just be spit into the exhaust and burned by the cat


Even if you could get better gas mileage with premium fuel, it wouldn’t get better money mileage.


I dunno’! With gas near $3 a gallon, and premium usually only 20 cents more than regular, at least where I am, a couple mpg better should be a better money deal. Not much but some.

I have not heard of 5 mpg better. But, when my Sienna was new, I bought regular. When I read the computer was shutting back to compensate, I started buying mid-grade for 10 cents more and mpg went up by 2, from 22 to 24 (mostly highway driving at 70mph on Interstates.)

In today dollars, $2.60 v. $2.70 = 3.85% increase in cost.

24 v 22 mpg was 9.1% increase in mileage.

Actual results will vary based on car and gas prices.


If it was anything but a Honda it would be slightly more believable. Hondas get about as good a fuel mileage out of their engines as anyone, and better than most. Honda cars are always near or at the top of their class for fuel mileage. Seriously, even my Honda lawn mower engine uses less gas than the old Briggs & Stratton and Tecumseh.

I agree with the others, find a new mechanic.


Your car was DESIGNED to run on premium. Those that aren’t, won’t get an improvement.


OK I checked and it wasn’t as DESIGNED as I thought it was.