I have to dissent here on the octane issue. The chances of pinging hurting your engine are really remote. Modern engines are built to take higher compression than old V-8s, so they can stand pinging better too. It may cause a degradation in performance because, as mentioned above, your computer will have to adjust the timing to compensate for the lower octane.
Speaking from experience as an automotive fuel system engineer, frequently the only reason cars are set to run at higher octane is to get a couple of extra horsepower so they can say “200 hp” in the brochure instead of “198 hp”. Kind of a sissy way to engineer a car.
I say give it a try, and if the pinging seems excessive or the loss of performance is annoying, use 89 or 91 instead of 87. 87 may be too big a cut from 93.
Are you mixing the cause and effect here? You mean, the engine configuration and tuning is changed to get the horsepower, thus requiring higher octane fuel; not that that fuel itself delivers higher power, correct? I mean, does not higher octane fuel have a lower heating value than lower octane fuel?
Way-ul, I’m just a country boy who likes working on his car, but I know that detonation is hot enough to melt aluminum, and if you have aluminum pistons, heads, or block, pinging will slowly chip away at all three. In fact, the major sign of detonation is aluminum flecks on the spark plugs. I know I don’t want specks of my engine melting off.
Now, ability to withstand higher compression (which could be achieved by smaller combustion chambers, different rods and pistons, milled decks and heads, and thinner metal gaskets in older engines) in newer engines has nothing to do with the ability of the material to withstand melting and flecking during detonation. That’s like saying that a balloon being able to expand further is less likely to melt.
Weeeell, not may, will. I’ve yet to see an engine that will perform just as well, fuel AND power wise, within even a few degrees up or down the timing. It’s going to be different, because it’s timed different.
Did anyone mention yet that too low of an octane will cause increased gas usage? My car (admittedly not a perfect comparison) loses about 20% mileage by switching to 87 from 89, and about 2-5% mileage by switching from 91 to 89. My vehicle also loses about 10 hp and equal torque from a lesser octane.
That, and to get a better emissions rating. Dialing timing too far back will leave quite a few unburnt gasses in your exhaust.
Wildest Bill, which car are you referring to? I’d like to know which one specifies that you can only use one Octane rating.
At any rate, some of the new cars have a nifty thing that detects how much ethanol is in the gas & adjusts things for running at the rate. Ford Ranger '99 is one. It might have specific gas ratings.
OK, then are there any possible reasons for someone to use high octane gas in their regular old car? Is it always a waste of money, or are there any conceivable limited circumstances where it might be useful?
And, could it be detrimental to your low-octane rating car?
To my knowledge, there is no disadvantage to using too high octane fuel. Well, not as far as damaging your engine, anyway.
Higher grade fuel is more difficult to burn, so it requires higher temperatures to burn completely. So you may take a performance hit and have increased emissions if you’re running 113 octane gas in your plain old 8.0:1 Chevette, since you won’t have the pressures and temperatures that joe drag racer gets in his 14.5:1 Challenger, y’know?
So since you pay more, get less performance, and less efficiency with higher grade fuel than your engine is designed to use, you’re wasting a lot of money (more per gallon, and use more fuel), I’d say you probably want to use the lowest grade fuel you can run without getting a ping or knock.
Anthracite: Thanks for the comments. How in the world do you fit so much information into one brain???
Lower octane fuel will start easier in cold weather. So putting high octane fuel in your designed for low octane car could be detrimental if you live in a cold climate.
My car is a Honda Civic Si which has a very high compression ratio engine. I have not tried using anything less than 93 Octane - the manual says to use at least 91 but no one sells 91. I read that only about 5% of cars need 91 octane or above but about 20% of gas sold is 91 or above - that means a lot of people are wasting a lot of money.
There is a place near my house that sells “spirit racing gasoline” that is 100 octane. It costs $3.40 a gallon. Does anyone know anybody that buys 100 octane?
**There is a place near my house that sells “spirit racing gasoline” that is 100 octane. It costs $3.40 a gallon. Does anyone know anybody that buys 100 octane? **
Yep. I used to. '69 Datsun roadster, after the second time we milled the heads in the engine. It didn’t run right until I bounced the octane through the roof.
I also seem to recall the car dieseling on shut down; I don’t remember what caused that.
Anthracite, welcome back. For a while there, I thought I might have to go back to school to learn physics and engineering
I used to mix aviation-grade gasoline with 93 octane pump fuel to get a 97 octane rating for my Cutlass. I was running a 455in^3(7.4l) V8 with 13.5:1 pistons so 97 was pretty much necessary. I could enrich the mixture a bit and run it on 93, but 1/4 mile times showed a significant loss (~15%) of power when I did that.
I’m betting you had a higher octane rating than 97. Avation fuel is called 100 octane but in reality it is 100/130. The lower octane is for lean mixtures and the the higher octane is for rich mixtures. Automotive octane numbers are averages between the lean and rich octane numbers. So you can’t mix the two fuels and then average the 93 and 100 because the numbers are measuring different things.
Incidentally, you wouldn’t want to put av-gas in any car with a catalytic converter, since it is a leaded gasoline.
