does expensive gas actually makes a difference?

Nah, BMW figures it will make you feel like you bought something special if they tell you to use premium... (sarcasm) Maybe you should have stuck with the Honda?

Yes it does. Your engine runs at compression levels that require high octane gas. Putting the lower octane in it will just force the computer to retard the spark curve and give you shitty performance. It'll run on the cheap stuff, but won't run like a Beamer unless you feed it the good stuff.

Doc

I get 100 miles more per tank on the highway when I run 92 octane vs 87 octane in my Jeep.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Apkesh wrote:

It somewhat depends on how you drive it. If ALL you do is steady highway cruising, you can probably get by with lower octane than if you have your foot to the floor. I think I would still use Mid grade as a minimum however.

If you want to get the full performance potential from your engine, use the higher octane gas.

------------- Alex

If they recommend 92 or above, that's because that's what they designed the engine for. Below that, you will have spark knock and the computer may retard your timing to undesireable levels. If too retarded, it may set a check engine code for the knock sensor (if it has one), thinking it's getting bad readings.

Running premium fuel for most cars provides NO benefit at all. It does not provide more power or improve gas mileage. High octane fuel just burns slower, that's all it does.

It does alot more than that as far as engine thermodynamics bud. High octane fuel will not detonate under high compression/high temps without a spark , thus allowing you to run higher compression pistons and giving you more oomph. A 9.3:1 compression gas engine with cast iron heads will knock like a woodpecker on 87 octane, will run great on 93 with the same ignition timing.

To run higher compression engines with lower octane gas, one must manually retard the timing, or on computer controlled engines the computer will do it for you. Either way it results in less HP.

No benefit WRT gas mileage? My old car

"\"Doc\"" wrote in news: snipped-for-privacy@adelphia.com:

Seems to me MPG isn't what's important here. The value to be calculated should be CENTS/MILE. If you can drive at a LOWER CPM with 93 octane then by all means go for it. If you do better with the 87 go with that.

87 octane = $1.79/gallon. 35 miles takes one gallon, or $0.051 per mile. 93 octane = $1.99/gallon. 43 miles per gallon or $0.046 per mile.

So cheaper "cents per mile" and better performance. Your point was?

Doc

"\"Doc\"" wrote in news: snipped-for-privacy@adelphia.com:

Exactly that one.

This is no difference in the quality between regular and preminum. The only difference is the point at which the fuel will self detonate(ping or knock). Higher compression engines(10:1 and higher) require preminum. You could damage your engine if the knocking gets too bad.

Most "premium" gasolines also have less sulfur than lower octanes. Thus they pollute a little less and should extend the life of a catalytic convertor by some fraction.