At the gas station last night I met an inquisitive new driver named Jill who was trying to decide why she should buy Premium gas. I decided to help her out with her decision, since she was driving a fairly normal econobox car: an early 90′s Toyota Camry.
First, let me explain why we need different grades of gasoline. Modern engines do 4 things to produce one explosion of power:
- suck air and fuel into the chamber
- compress the air and fuel inside the chamber
- detonate the compressed air and fuel, using a spark from the spark plug
- release exhaust gases
This happens thousands of times each minute while you’re driving, and is a fairly refined process. The amount of fuel is automatically decided by the engine computer or carburettor and the driver directly controls how much air is let in.o The compression ratio is a static amount of pressure a piston puts on the air and fuel, which allows it to burn more effectively. More compression creates more power and less compression puts less strain on the engine. Turbochargers can complicate this process by compressing the air before it enters the engine, allowing the static compression ratio of the engine to be lower while still producing reasonable amounts of power.
Why buy high octane?
Compressing air and fuel creates heat, and in some cases can cause the air and fuel to explode without the use of a spark. That causes the delicate balance of the engine to go awry and for an instant the engine is fighting against itself for all its worth. This is called ‘pinging‘ or ’knocking‘.
To control this, gasoline is given an octane rating, which indicates the combustion point of the particular mix of gasoline. Regular gas is generally rated between 87–92 Octane, with Plus and Premium ranging up as high as 98 Octane. Grassroots racers refer to this range as ’Pump Gas’, and many racers are proud of their ability to push the limits of common gasoline. Ratings higher than 98 are considered race fuel and are usually illegal for the street.
Higher octane ratings only indicate a higher detonation point and resistance to pinging at high compression ratios (or high-powered turbochargers and superchargers). While your owners manual can certainly give an indication of what grade fuel you should fill your tank with, it’s a safe bet that if you can hear pinging while driving (normally when you press down the throttle pedal hard while at low RPM’s) you should step up a grade.
Conclusion
For almost every car owner (excluding very high-end sports cars), higher octane fuel is a waste of money and offers NO benefit.
Well. i agree with most of what you have said. However, there are more and more cars out there that require premium these days. Just about everything with a ford v8 of recent make gets enough better mileage out of premium that it makes sense. Most anything with a turbo will run better with premium. Like a wrx or a saab.
so say for a b16a1 non-turbo you wouldnt recommend premium? I’m sure there are other advantages with higher octane, such as cleanliness? – i may have been previously misguided
Thanks
A b16a1 is definitely high compression enough to require Premium. It falls under the category of a high-end sports car, because of the way the engine has been tuned. It’s more of a race engine than anything.
As far as cleanliness goes, some higher grades of gas include detergents of debatable usefulness. Some of them do a good job, but a solvent like SeaFoam is much more effective and well-tested for what it does.
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