Because with a very heavy load the ECM can keep the timing further advanced with the premium fuel with the 87 it is retarding to prevent knock. Without the load it doesn't matter.
The only time I see better
See above about the ECM being able to run more timing advance on the higher octane.
Which was a shipwreck, not corporate policy.
Hey Bob,
Several points, first since you "always" use premium, then it would be safe to assume that you haven't run regular so you are just spouting the line.
Furthermore all cars made since 1980's are designed to run just fine on regular. If you are getting better mileage with premium, then your car is not properly tuned. The "premium" fuels have no more energy in them than the regular grades they only have a higher octane. If your car does not ping it knows no difference.
The average spread between regular and premium is usually 20 cents a gallon. If you get 15 miles per gallon and drive 12,000 miles a year that's $160.
If you drive more miles or get less than 20 MPG then it will cost you even more.
Roger Shoaf wrote: /snip/
/snip/
I have two post-1990 high-performance vehicles (i.e. more than 100 hp / liter) vehicles in my garage. One is turbo charged and the other is a Honda VTEC. BOTH of the owner's manuals say that premium (91 octane or higher) fuel is to be used. They also go on to say that if you use lower octane fuel then the performance of the engine will be reduced to prevent pinging. I don't agree that reduced performance of a high-performance engine is "just fine".
What does volatility have to do with octane ratng or knowk?
At least it isn't a waste of money.
CBVAC is right. Burning premium in a vehicle designed for regular is just like putting dollar bills in the toilet and flushing them down the drain, except Bush and his millionaire buddies are getting your discarded dollar bills.
The carbon fouling caused by premium in an engine not designed for it is what is really expensive.
No, it does not hurt anything (other than a few horsepower) to burn regular in a modern car that is designed for premium. Now, on a pre OBD car designed for premium, it will hurt to burn regular. We are talking about cars built before the early 80's.
I don't think that's what he meant to say although he did say "all cars". It is true that some performance engines should run premium but there is no advantage in it under most conditions for the vast majority of vehicles.
Volatility deals with more than evaporative rate at a given temp.
According to Websters:
Volatile:
c : tending to erupt into violence : EXPLOSIVE
b : characterized by or subject to rapid or unexpected change
The damage done is all that matters not to mention that at the time there was alot of criticism of Exxon for the speed or rather lack there of of it's response.
The burn is slower on a high octane fuel, the higher the octane, the more resistant the fuel is to pre-ignition, and spark knock issues. You can run a higher compression ratio on a higher octane fuel, and not worry too much about timing issues (retarded timing) since the fuels not going to try to ignite prematurely...(think diesel) You would not dream of running gasoline in a diesel, well...putting low octane fuel, in say...a
12:1 compression car is like doing the same thing....your going to get a fuel that will ignite far sooner than is should. Remember, higher the compression, the more you pack the charge so to speak, and like a diesel that requires the rapid compression of the air in the cylinder to ignite the oil, the same will happen in a gasoline powered vehicle...higher the compression ratio, the more heat is generated when the charge is compressed, and you reach a point, with engine heat added to it that a gas engine would in short order destroy itself from the force and heat generated at the wrong time of the compression stroke from the gas charge firing off too soon.EVERYTHING!!!!!!!
Volatility in it's usual technical meaning refers to evaporation. i.e.
1 : readily vaporizable at a relatively low temperature.Which is probably what he or she was thinking of.
It has other common usage meaings that are applicable of.
Good discusison. Here's a nice writup on the performance impact of different fuels:
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