Does E46 really require 91 fuel?

Your kidding, right? Your comparing the fuel requirements of a VTEC ricer to an M3 engine?

Yes. The E46 M3 requires 91 minimum. 93 is better if you can get it.

What you say would be true were he talking about standard tune E46. But an M3 is not a standard tune engine. Yes, there is *some* flexibility in the timing provided. But he's driving a freekin M3 here. Pay the extra 10 cents a gallon man.

Better yet, just send me the car and I'll put the right gas in it...

So what's the difference? Why S54 would have problems on low octane gasoline while. VTEC does not? I thought VTEC works in a more intensive mode ( usual RPM band 5 - 7k ) while S54 stays most of the time in mid-low RPM band (if not being raced ofcourse :) AKI is detrimantal in high RPM mode or is it closely correlated to the power curve? I hope you draw your recommendation no from what is written in the manual.

I'm in SoCal there is a 50c difference.

Then don't drive.

If you can't afford to maintain the car properly get a donkey and cart. BMW has great cars built by great engineers whoknow what they are doing. If they say use super unleaded, this is easy, you use super unleaded.

RPM has very little to do with octane requirements.

Higher octane fuel allows higher compression and more ignition advance, thereby improving thermodynamic efficiency.

A

The highest octane requirement occurs at the point of maximum pressure in the cylinders, and this is at the RPM where max torque is achieved. Since this engine has a relatively flat torque curve, it needs high octane all thru the middle RPM range.

Frank

Assuming that you are replying to me...

VTEC is just Honda's method of varying the valve timing. It accomplishes the same this as VANOS in BMW engines, (but employing a different mechanism) allowing a more advanced valve timing at higher RPMs. Neither VTEC nor VANOS is the primary factor as to whether one needs to use higher octane fuel. The compression ratio and timing for the S54 engine were designed with the use of high octane fuel in mind.

Will it destroy the engine to use lower octane fuel? No... probably not.

Will the ECU adjust to compensate for the lower octane (faster burning) fuel? Yes it will (within reason).

Will you get the same engine performance burning lower octane fuel? No you will not.

Did you pay a large wad of cash for an E46 M3 (instead of a 330i or

325i) so you could then look to save 10 cents per gallon and have less than optimum performance? Only you can answer that question...

between 89 and 91? You left coasters are getting the shaft! I have sen as much as 20 cents difference but most stations here it's only 10.

pretty pathetic if you ask me! sell the car!

say Lemminings? :)

SoCal gets the shaft for everthing. Tried to buy a house in OC or SD area recently?

By all means, if you feel you can garner enough internet advice to build a better car I await your production schedule. That's a highly modified high compression engine you are referring to. If you've ever tuned a carb or adjusted a distributior on such an engine your question is immediately answered. Even with the electronics, the engine will operate much more effeciently with the proper fuel. Whatever it's your car. You could likely even save some more by using cooking oil in your crankcase than that synthetic oil the other "lemmings" use on BMW's advice.

Thanks for a good explaination, Fred. Actually, I didnt pay a large wad of cash for the car . I picked it up used for a price comparable to new Acura/Hondas. My queston stemmed from the fact that I drive at least 5 days a week in bumper-bumper 10 mph traffic therefore I dont think it will make a difference in performance under these circumstances. My only concern is if it will have any detrimental effect on engine. I didnt mean to disrespect excellent german engineering. ;)

sell it now!

It will not have a detrimental effect on the engine. It makes your engine slightly less efficient. I came from the Porsche side a few months back because I needed a car that could be used as a commuter car as well as have a little sportiness in her. The Porsche had a heavy clutch and a 5 speed, not exactly commuter friendly. The Porsche also had and engine that required

Nope. Wouldn't even be interested.

I don't think an M3 is a very good choice of car for driving under those conditions. Maybe you should consider getting a car better suited to you use?