QUOTE (samir0189 @ Sep 13, 2010 - 6:12 AM)
QUOTE (b22ri22an @ Sep 13, 2010 - 3:30 AM)
a stock 5s in the US will run the same on 87 octane as it will on 93 octane the only difference will be how much you pay
x2.
HectortheRican is exactly right. Octane rating is a measure of the detergents used in the fuel. A high compression engine can detonate the fuel when the piston compresses the fuel in the cylinder, BEFORE the spark plug actually ignites. You don't want that to happen. So with a high compression engine/turbo engine, you need a higher octane fuel to ensure that there is no detonation before ignition (knocking.)
With the 5S-FE or 7A-FE, you have an economy engine. Not a high performance engine. You're literally throwing your money away by pumping premium. Your car will run exactly the same on 87 as it will 100+. Thinking that your car has more power or that you are getting better gas mileage simply because you pumped 91 is nothing more than the Placebo effect. However, for those of us with the 3S-GE BEAMS engine or the 3S-GTE, there really is a need to pump 91+. It will resist knocking and avoid costly engine damage.
Not all fuels are equal though- if you have the chance, pump fuel from a top tier station. If there's a no-name gas station on one side of the street selling fuel for $2.75/gal and a Shell on the other side of the street selling the same octane fuel for $2.80/gal, pump the Shell. No questions asked. Top tier fuel truly is better.
Links to read and learn from:
Top Tier Fuels.Car and Driver- Regular vs. Premium.