Thu 24 May 2007
I was going to talk about this in yesterday’s post about Costco gas economics, but I held back just because I knew some people would object, but I’ve done a little research, so to Sam’s comment, this is just my humble opinion.
A couple weeks back I was enjoying Click and Clack’s weekly Saturday Morning show ‘Car Talk’ (which you can find on your local public radio probably) and they addressed the question on whether or not premium gas is really essential for cars that supposedly require it.
Octane ratings in gasoline measure its ‘knock resistance.’ Knocking occurs when fuel in a combustion chamber ignites before it should.
Apparently according to Click and Clack, cars until about the early 90s required the correct octane gasoline, or suffer extreme knocking and vibrating under the hood. It wasn’t until the early 90s that car manufacturers installed ‘knock sensors’ to prevent this from happening if you are using the wrong octane.
The knock sensors basically slow the speed of the cylinders to match that of a regularly tuned car that doesn’t require the special octane ratio.
Philip Reed of Edmunds.com said that the only advantage now to higher octane gasoline for your luxury/sports cars is that you can make it to 60 mph in half a second less time.
Here are some more sources:
NPR’s Car Talk - Click and Clack on “Car Talk” diss Premium Gas.
USAToday - Experts say that these days there isn’t much difference at all between premium and regular, and even challenges you to go back and forth to test it.
Edmunds.com - Modern sensors have made engine knocking a thing of the past.
ConsumerEnergyCenter.com - Knock sensors have made high octane obsolete. Using premium to clean your engine is also a myth.
CBS2.com - A mechanic of 25 years says that high octane is much less important these days with sophisticated on-board computers and knock sensors.
straightdope.com - this article warns against using regular in a car that requires premium if you do not have knock sensors (if your car is more than 15 years old).
May 24th, 2007 at 11:09 pm
From the Edmunds article that you pulled info from, there is an excerpt from the Volvo manual:
“Volvo engines are designed for optimum performance on unleaded premium gasoline with an AKI (Anti Knock Index) of 91 or above. The minimum octane requirement is AKI 87.”
So there, it’s not misleading is it?
May 24th, 2007 at 11:18 pm
Here is my WRX’s engine manual:
“For optimum engine performance and driveability, it is recommended that you use premium grade unleaded gasoline.”
So there you have it, Volvo and Subaru aren’t misleading anyone. There are cars the REQUIRE it and there are cars that RECOMMEND it.