the MPG will also drop as the timing is retarded. i went on a road trip with a fellow corvette owner who used 87 and i used 93 and every time we filled up he took 2 or more gallon than i did .

 

which defeats the purpose of buying a performance car

 

Other than the fenders falling off, nothing will happen. It's almost as bad as driving the car in the rain or, OMG, taking it through a car wash. These are very fragile cars and break easily. Your best bet is to just leave it in the garage.

 

Don't believe any of these guys! Trade that car ASAP!

 

I run Mid Grade (89) most of the time. I also put in Premium (92) about every 3rd fill-up or so, this I do for the additive packages that usually provide a better (or more) detergents that help keep that beautifully simple OHV pushrod motor in spic and span condition. As was stated above, based on the performance the engine sees from the current conditions it retards or advances the timing ultimately deciding at what compression ratio to ignite the A/F mixture in the cylinders. Unless your Racer-X, you really won't notice a whole heck of a lot of difference between the 89 and 92 octane. My guess is that if you run 87, you'll likely notice some knocking under moderate to hard launches. If you do hear the knocking; slow down - this is hard on the valvetrain/upper end of the engine. When all is said and done, the consequences of using 87 octane are minimal. I wouldn't use it exclusively though

 

i would do the math,gas cost vs the drop in mileage to see if you are saving any money and how much

 

This is a myth. There are detergents and additives in all grades of gasoline. Detergents are added to the tanker when it leaves the refinery, and mid grade is usually a blend of low grade and high grade. Different brands of gas use different detergent/additive packages, but they use it in all octane levels. The difference in levels of gasoline is because of octane, not detergents. Octane is the resistance of the fuel to burn; the higher the rating, the less likely it is to pre-ignite, which is what "knock", or detonation, is.

The whole "higher grades have more detergents" thing was perpetuated by strong ad campaigns from the fuel companies about 10-15 years ago, back when gas was so cheap. Ironically, people who thought they were doing something "special" for their car by putting in higher octane gas than what it called for were actually causing more harm than good. If an engine is designed to run on 87, and you're filling it with 93 because you think it's got more detergents, you're causing an excess in carbon build up and decreasing the car's overall performance. Why? Because the 93 is more resistant to burn, so the combustion cycle isn't igniting all of the fuel, and some unburnt fuel will make its way through the system, leading to carbon build up and accelerated emissions equipment wear.

I've got a 2002 Honda CBR600F4i motorcycle that the previous owner thought had to have premium fuel, when it's really made for 87. He used premium exclusively, and now the thing has a bunch of carbon build up in it; if I use anything less than 89, it'll knock (carbon build up can increase compression ratio, meaning you have to use gas that's more resistant to knock. i.e. a higher grade of fuel).

You can find countless references that verify this out there, but here's just one:
http://www.edmunds.com/advice/fuelec...3/article.html

 

My fenders didn't fall off, they just cracked...

You'll be fine, I tried 87 a few times to see what the diff was...

 

Not to be obtuse here, but I really don't believe there is more mileage in a gallon of 93 vs a gallon of 87. They both likely have approximately the same energy per gallon. The difference is in the volatility of the fuel based on the additive package as the truck leaves the refinery. 87 Octane is far less stable at temp, and tends to ignite in a far less predictable fashion, thus the whole retarded spark issue. That said, I will concede your point of better mileage only if the car is driven aggressively. Even if wee look at the math,

The cost delta between 89 and 92/93 around here is $0.20 at a minimum. on a sixteen gallon fill up, that's $3.20 - almost a gallon or in my case about 17 miles extra per fill up. I 'd say I fill up about 7 times a month - that's $22.40 a month - or $268.80 per year - Heck, that 6 month's insurance premium.

 

On my last fillup I put in regular on purpose.

I haven't noticed any difference.

 

I always used Amoco ultimate, or now BP premium. But never tried to put in the lower grades. Maybe i should try it and see what happens.

 

You can get 93 octane? Wish I could.

 

and you won't.

Is there a difference between fuels? Sure.

But it's probably more about marketing than science.

 

 

i have seen 2 similar corvette on a long road trip the owner using reg needed about 2 more gallons per fill up than myself.

 

I have to disagree with most of the posts. Use 91 and 93 if you can get it. I just bought my 2007 (upgrade from '96 LT4) and I get some knocks even with the 91 that I can get here in Los Angeles.