What's the deal with gasoline octanes?

Question

My car manual calls for gas with an octane rating of 91. Most stations sell 87, 89, 93. I have heard the higher the octane the cleaner it will burn but less mpg, and vice versa. Performance car- 07 Subaru WRX (Turbo). Should I go over or under?

Answer 1

You could go over, or do a blend of 89 & 93. All 89 octane is is just a blend of 87 & 93.

Answer 2

Subaru specifies a 'minimum' octane rating of 91 for the WRX. The higher the rating, the LESS volatile the fuel. That means higher flash, or ignition point. It takes more energy/heat to ignite it. Nothing more.... not more power, not less mileage/economy. Your engine is turbo charged, which force feeds it, (in simple terms), raising realized compression ratio and creating more heat in combustion chamber, than a standard performance vehicle. The added heat is retained in engine hard parts and can cause fuel mixture to ignite before spark is delivered, (much like a diesel eng. operates) Hense 'preignition or detonation .......pinging this condition prolonged is fatal to an engine. Higher octane fuels are simply more resistant to igniting. They will not give any more power to an engine not requiring it, & may even offer less performance in standard compression engines.

Answer 3

I agree with Subgenius. It's best to err on the side of caution and go with the higher octane, but you can achieve a 91 octane mix by blending a higher octane fuel with a lower octane. That is how mid-grade fuels are made. You could go with something close to a 70/30 blend ratio.

Answer 4

go over is better, basically the higher the number the easier it is to burn more volatile. if u use 87 it will burn too quickly and while your piston is going up the explosion will want to push it down before its neccessary this is what is called pinging or knocking which can cause serious engine damage. since your car has a turbo the pressures inside the combustion chamber are so high that you need a fuel that wont ignite before its supposed to therefore the higher the better on your car

Answer 5

With a turbo car it is ALWAYS better to go with the higher octane, if you use lower octane your car will wind up with all kinds of expensive troubles. a turbocharged cars function is to shove air into the motor faster and the better the gas burns the better the car will run, with low octane you will risk detonation (blow your motor up). every car is designed to run at its peak efficiency level, car manufactures spend millions on designing their motors (trust the manufacture).

Example: a Civic only needs 85 octane because it is designed to be a economy car, a WRX is designed to be more of a sport car, therefore needing 91+ octane. besides if you use 93 octane you will gain a few more horsepower.

Answer 6

larger octane rated gas's face as much as detonation, or "ping" it is in simple terms a difficulty in case you run larger compression ratios. it is in simple terms a element in intense overall performance automobiles like Corvette. I actually have a Taurus SHO that recommends intense attempt gas, additionally. No a Corolla won't earnings from it. it would in simple terms be a waste of money.

Answer 7

higher octane =more power, but less MPG. Use the lowest grade that the car runs on without spark knock

Answer 8

Difrant kind of cars need diferant levels of octane that simple like racing cars need gas with lots of octane while most regular cars dont need as much justt settle for unleaded

Answer 9

You need higher octane for higher compression. ~
With higher compression your power and mpg goes up, unless you just waste the extra power.

Answer 10

Over it's best although most expensive! At least do 89 if anything.