[Small Yellow]

Now truthful question, not that I would do it but because of curiosity, would using cheapest gas from chevron damage the engine in the M3?

[Elie335]

bullsh*t, a simple proof; log your ignition timing with 91 octane, and log it with 93 octane, you will notice why 93/premium fuel should be used in performance engines.

[michaelthepsycho]

Originally Posted by Bols

95 is the lowest we got here, and i always put shell vpower 98 in mine. The difference (especially over highway) in mpg is clearly visible. High pressure injected engines should just decline to run all together when the owner puts anything but premium fuel in them

... Don't use the Euro RON number to base your numbers. 95 RON is pretty much 91 AKI. No need to go 98 RON (roughly 94 AKI).

[Couper93]

It's really pretty simple (this is by no means a scientific explanation, car guy language only):
In simplest terms, Octane with the temperature in which gasoline will burn. Higher the number, hotter the temp. What does this mean?
With higher temps, you can have higher compression, with higher compression, static or organic, you can have more performance.
Timing is a big factor in HP. Typically if you have a car that has more timing or advanced timing, you have a higher performance car.
Formula is as such ( again car guy language), typical rule of thumb: more octane + more compression + more timing = MORE POWER..
However, in todays computer control vehicles, you can't pop the hood and turn the distributor and gain 10 HP like the old days. Factory direct manufactures timing curves are capped, regardless of fuel. Knock sensors have eliminated the need for premium fuel in 'economic' cars. However, the performance or 'factory' dialed in performance cars are engineered to peak with 'premium' fuel. Manufactures tweak timing and compression for max, to a point, power and in doing so with require a premium fuel.
Does that mean they will run without premium? Of course.
Does non premium fuel hurt the engine? No, knock sensors prevent that
Does non premium fuel hinder performance and mileage of a 'performance or premium fuel' engine? Yes

Also another thing about Octane, very high octane gas (race gas, 101, 110, 120) is not a good idea unless you are running a static compression of over 13:1 or turbo/supercharger. High octane gas requires high ignition temps but actually burns cooler.....odd I know....and can cause damage is abused or used in a situation that is not designed for such.

[CJ421]

Stupid article - to which less-than-astute readers will go forth assuming premium fuel is a scam. Way to mislead the readers ...

Why would BMW require 91+ if they didn't have to? Wouldn't it be a selling point if the car was able to use 87? C'mon ...