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Old 02-04-2006, 01:31 PM   #25
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Join Date: Sep 2005
Location: Minneapolis/St. Paul, Minnesota, USA
Posts: 3,308
Originally Posted by eslai
Sorry, it sounded like you were saying that the higher octane fuel makes power, but that regular octane fuel is fine. I just wanted to clarify that. If people get that in their heads, it might make penny pinchers start doing bad things.

But, I think it's also important for people to know that lower octane fuel WON'T blow up your car. If you end up having to fill up where they don't have the proper octane or anything close to it, you can still drive on it, but you would definitely have to do the "drive like there's a raw egg on your gas pedal" thing. Drive like a grandma, so to speak!


A couple of points. There is a difference between the Power an Engine can make and the amount of Energy contained in the Fuel.

Gasoline contains about 30,000 Calories in a Gallon (one of the most Energetic Fuels in existence). But, once you start adding other compounds such as De-Icers, Octane Boosters, Lubricants (yes there's some light Crude in Gasoline), you no longer have a full gallon of pure Gasoline, it's been dilluted.

Unless those additives in combination contain 30,000 Calories/gallon or more, you have lowered the energy content of the mixed gallon of Fuel.

And few additives contain that many Calories/gal. so the higher the Grade, the less energy it contains. Your Engine may well make more Power (because the DME isn't retarding your timing), but you will not get as high an MPG from it - you will burn more of it to produce the same amount of work. This is significant because the closer you can stay to Raw Gasoline, the better your Fuel Economy will be and the lower your operating costs.

But before anyone thinks they can Cheat the Fuel Gods and fill-up half & half with Reg. and then Premium thinking they've saved a couple bucks, but raised the Octane content sufficiently to operate properly, realize that the different grades have different specific gravities, so one will Float on top of the other and you'll be burning Reg. for half a Tank and Premium for the other half.

I'm not sure I fully agree with your statement regarding not blowing up your Car should you run on 87 Octane. Aside from the issue of Knocking, you can have a variety of unburnt combustion products running through your Cats which will shorten their life as well as that of the O Sensors. Plus, any ill effects on will be totally dependent upon circumstances. You may not have a problem driving an empty Car though the Nebraska Flatlands on a 30 Day at 50MPH with the CC on, but load up the Car with Passenger, Luggage, full Fuel Tank, or drive Up the Rockies or through the Desert at 120F, and you could create serious problems. Ambient Temperature, Altitude, and Load are major contributors to Knock. Ever notice when you hear an old Car knocking it's usually accelerating or going uphill?

A better suggestion would be to carry some Octane Booster (a couple cans at least) if you're driving through a strange area where you're unsure of the availability of the proper Fuel. Also, inflate the Tires a couple of extra pounds to decrease the Rolling Resistance and reduce the Load. Don't run the AC or any other component which might cause the Engine to run Hotter either. Hope this helps...

Happy Motoring!... Jim'99

Last edited by MNBoxster; 02-04-2006 at 06:24 PM.
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