On the occasions that I find a station with 93 octane, I usually fill her up. I really don't feel a difference in my Mini with the different octane, but then, I don't use 93 on a reg. basis. I usually use 91 because it's easier to find where I'm at.

 

I think you have to go for a few tanks of 93 to see the difference to make sure it is all there. also, you have to be pushing it. shrugs

 

no one seems to be able to suggest "how much extra" is at stake...

Is this discussion about getting one hp or ten hp?

 

As premium grade fuel varies by locale (91 vs. 93) I've had the opportunity to use both and can detect no descernable difference in regular street driving. Maybe on a dyno, or at a track event there may be some measurable, statistically significant variance. I have yet to see both 91 and 93 offered at the same station. In my area, typically the offerings are 87, 89 and 93 octane with one station offering 87,89,93 and 94 octane blends.

The MINI's ECU will adjust your timing accordingly to prevent pre-detonation. Go with any medium or premium octane rating, you won't have a problem in normal driving.

 

My experience:
Stock MCS + 91 octane = no knocking
15% pulley + 91 octane = knocking
15% pulley + 94ish ocatne mixture = no knocking

 

timing retards to prevent knocking. timing doesnt adjust to the gasoline. retarded timing is just that. retarded. it means less power from gasoline. subjective or otherwise, it cannot get the best efficiency without high octane. 93 is just the beginning of what it can use.

 

It is entirely possible that you could use 93-, 91, or even 89-octane gas all day long for normal street driving and never get any knocking. In that case, the computer will never need to retard the ignition timing, and you'll be getting maximum efficiency from the engine/gasoline combo, because all else being equal, the specific energy content is higher for the lower grades of gasoline.

The only way to know for certain would be to hook up a real-time scanner to the OBD-II port and log the knock sensor voltage while you're driving. The "sweet spot" for gasoline grade would be whatever octane is required so that you only get light pinging under heavy load.

Scott

 

I figure if people cut back a little on the number of Starbucks; i.e, make your coffee at home, then the cost savings between purchasing 91 or 93 Octane is moot.
93 Octane and Eight O Clock Coffee all the way for me! :-)