premium unleaded, worth it or not?

In My Humble Opinion
1

Around here, premium unleaded is about $.20 a gallon more expensive than regular unleaded gas.

If you drive an average car (more Honda Accord than Ferrari), is it worth the extra money to get premium gas?

2

I’ve been told that if your vehicle ‘pings’ (under normal driving conditions), move up in octane until it stops. Other than that, stick with what you have.

3

Unless your car requries it, it’s not worth it. SOme cars may be able to take some advantage of higher octane by advancign the spark somewhat but you are not going to recoupe the cost of the gas that way.

Higher octane = slower combustion. Cars that take high octane have higher compresion ratios which require that the gas can remain ‘unburnt’ until properly ignited (as opposed to igniting from compression).

4

# has it right.

To be more specific:

  • Straight heptane (a string of 7 carbon atoms with 16 hydrogen atoms attached) will pretty much make any gasoline engine “ping” or “knock” (have a secondary explosion in the cylinder).
  • Straight octane (8 carbons and 18 hydrogens) is pretty much “pingless”.
  • An “octane rating” measures how close a fuel blend gets to the ping-ingness of pure octane. (fuel blends have a wide array of different hydrocarbon molecules).

Different methods are used to bring up the octane rating of a fuel, other than just changing the octane:heptane ratio. For example, adding benzene is one of the cheapest (therefore most common).

This all ends up saying, much more boringly, the same thing that # did in two sentences. Use the lowest octane at which your engine doesn’t ping.

JonTheFormerChemEng

5

Thanks, k2dave! I’ve learned this from the chemical side, but I never took the time to study it from the engine side.

Jon

6

Actually, high octane gas can damage engines that aren’t designed to use it. By delaying ignition (which is what high octane does) you can have combustion taking place outside the cylinder, which is a bad thing.

Also, if your car is tuned up properly, you may very well get worse MPG since high test gas has less energy than low test.

7

If your car has a knock sensor, it will not knock or ping on the cheap stuff but it will not achieve it’s greatest performance, either. In such a case, using premium fuel will cost more and will not improve fuel mileage but your acceleration will improve.

If the gas guage says 92 octane only, you had best stick with it. Otherwise, read your car’s owner’s manual to see what the manufacturer recommends.

With the exception of high performance machinery, using anything above 87 octane is a waste of money and, as indicated, may cause harm to your engine.