Here's a technical question for the gearheads among us:

I know that higher compression motors require premium fuel because it is less volatile, meaning that it is less likely to burn prematurely. As a fuel's octane rating goes down, it is more likely to cause premature combustion (knocking), and this will lead to reduced performance, and reduced fuel efficiency.

I also know that modern engines have built-in countermeasures that will compensate for knocking by retarding the valve timing (or something like that).

Here's the question, will these countermeasures reduce the life of the motor in the long-term? If not, what are the drawbacks of using lower octane fuel other than reduced performance and efficiency?

is the difference between 91 and 87 something youd like to really worry about.

Use 91, and forget it. There are more important things to attend to in life besides gas.

Well said. :lol:

1-No
2-No other drawbacks that aren't subjective

I live in IL. price difference between 87 and 93 octane fuel is .30c per gallon. I am getting about 330 miles per fuel tank on average. That gives about 45 fill ups a Year with average 15K miles per year. Usually it will be about 16 gallons of fuel per fill up. 16 gallons times 0.3c is $4.80 let's say $5 even. At 45 fill ups it comes to $225 a year, and that is with driving 15K miles per year! Don't we have a bigger problems to worry about? :lol: Just use the right fuel. It won't hurt.

i'm gonna pump some e85 in the 5er and see how that affects performance

i hear your mileage is reduced

i'll report back

this could save you 30 cents a gallon

Are you worried about the long term effect on your wallet? It's about $3-$5 per tank full difference. I just went through this with my mother-in-law. She has a $50K car, and she is worried about $3/tank full?!!!

Let's see, long term effects of using lower grade gas? How about not having engine repairs covered even if you are under warranty. The owners manual does not say "91 or Premium octeane recommended" it says "required", which to me means using lower octane fuel can give the dealer a reason not to cover a repair even if the warranty is still active. Other than that? You're good :twoup: I use the highest octane available, which for me (SoCal) is 91.

and that kind of logic, my friend, is why the price of fuel in general, and taxes, are going to keep creeping up and up, cent by cent, for no other reason than they can and guys like you say whats the difference, it's only $3 per tank. Or so what, my taxes are only going to increase by $100 a year - no big deal.



Sorry, one of my pet peeves. I digress.