[Drothgeb]

I was just looking through the manual for my wife’s new M40i. And it says 89 AKI fuel minimum, 91 AKI fuel preferred, but 93 AKI for the M Performance engine. The top of the engine does say M Performance, but is it the one that requires 93 octane? Or, are they referring to the full M engine?

I know it will likely run better on 93, and maybe even get better mileage. But for my wife’s regular shopping and grocery trips, I’m guessing 91 is fine.

[suby01]

Based on my understanding. M Performance is in the X3 M40i. The X3M has an M engine.

Even though it sounds the other way around, the M Performance is actually a lower version of the M.
To answer your question yes you have M Performance.

[wdeerfield]

all to save $2 a fill up...

[GS - X3]

I wish that I could even find 93 Octane gas...

[Drothgeb]

Originally Posted by wdeerfield

all to save $2 a fill up...

Thanks for no help there dude. Don’t think I ever mentioned that I was looking to save any money. There are other factors I’m considering….

Under the gas cap lid it clearly says 91, but the manual says 91 or 93 depending on the engine. If the engine is not setup to take advantage of 93, then it may actually perform better on 91.

In my area 91 and 92 are easy to find, 93 is not. So, can I use 91 or 92 from the stations I normally go to. Or, should I make a special trip the station that sells 93. Which btw, yesterday, was almost a dollar more a gallon that the station that I normally use to get 91.

We also do long road trips. So can I pull over at almost any station that offers 91 or, should I wait for stations that offer 93. Which in some areas are not that often.

[titomi]

91 or 93... not that big of a difference to woth the headache.

[383vett]

Hard to get anything above 91 in California.

[M113]

As the other CA residents have pointed out there's no logical way to get 93 out here so I foresee zero issues running 91 in other parts of the county where 93 is prevalent.

The issue happens when people cheap out and fill 89 into their 91+ required car just to save a couple bucks, oof

[Alias1431]

Yeah, only 92 around my town.

[freshxdough]

All BMW require 91 octane 89 minimum. 93 if you're on the east coast.

M40i is considered an MPA (M Performance Automobile). It is not an M engine but you could say it is inspired by M. Most Mxxx cars have louder exhausts, sportier characteristics and typically M sport body and trim.

[briguy80]

Originally Posted by freshxdough

All BMW require 91 octane 89 minimum. 93 if you're on the east coast.

M40i is considered an MPA (M Performance Automobile). It is not an M engine but you could say it is inspired by M. Most Mxxx cars have louder exhausts, sportier characteristics and typically M sport body and trim.

Why 93 for the East Coast vs 91 elsewhere?

[freshxdough]

Originally Posted by briguy80

Why 93 for the East Coast vs 91 elsewhere?

I'm not where exactly off the top of my head but I believe it has to do with climate and fuel quality. It's just a known fact the east coast gets 93 and west gets 91. I'm not sure where it splits down the USA for 91/93. Anything 91 -93 is perfect. 89 is minimum and should only be used when absolutely necessary. Don't expect peak performance with anything lower than 91. Lower octane fuels can also cause a bit of slight rough running on cold start as well. ISTA can read out tank fills to see if you have been filling up with top octane fuel or lower.

[strohw]

Originally Posted by briguy80

Why 93 for the East Coast vs 91 elsewhere?

Some states like California have laws in place that limit octane at the pumps.

[Coi]

Originally Posted by strohw

Some states like California have laws in place that limit octane at the pumps.

There is no law in California limiting octane. Some gas stations here sell 100 or even 103 AKI. What the laws do limit are certain additives that can be used to increase the octane rating of gasoline due to their harmful environmental or health effects.

California's premium gas originally went to down 91 when the state banned MTBE due to it polluting the water supply including drinking water. It may also be carcinogenic. Since then most other states have followed suit but companies supplying gas to CA never had a reason to make new formulations to increase the maximum octane again. The most common additive currently used to increase the octane in the US ethanol. CA limits ethanol percentage in regular gas to 10% (E10) while some states allow up to E15 to be sold as gasoline.

There are old patents that would allow for a 92 octane California-legal gas but no one wants to pay the licensing fee.

[Zachp13]

My M40 said 91 preferred and my new X3m says 93 preferred on the gas flap.

[Scottatah]

In Alberta Canada, we generally have 87, 89, 91 and some stations have 94 (at least for Petro Canada which is what i frequent)

[Drothgeb]

Originally Posted by Zachp13

My M40 said 91 preferred and my new X3m says 93 preferred on the gas flap.

Ahh, that’s what I was looking for.

It’s funny, I was in PA yesterday. The Sheetz had Flex, E15, 87, 88, 89 and 93, but no 91.

[Drothgeb]

Originally Posted by freshxdough

I'm not where exactly off the top of my head but I believe it has to do with climate and fuel quality. It's just a known fact the east coast gets 93 and west gets 91. I'm not sure where it splits down the USA for 91/93. Anything 91 -93 is perfect. 89 is minimum and should only be used when absolutely necessary. Don't expect peak performance with anything lower than 91. Lower octane fuels can also cause a bit of slight rough running on cold start as well. ISTA can read out tank fills to see if you have been filling up with top octane fuel or lower.

I see you’re a tech, so I’m wondering why lower octane fuel causes rough running when cold. It ignites and burns quicker than higher octane, so I would have guessed it to be better for cold starts.

From responses, it seems design spec is for 91. Can it automatically adjust the tune to take advantage of 93 or higher?

[Kinsella]

Since this has become a bit of a survey, here in North Carolina it's 87, 89, 93. I have never seen any other flavors.

[nord1899]

A lot of if you see 91 vs 93 as top octane depends on either state laws or elevation.

Here in Utah (I'm at 5000 feet), our gas stations are typically 85 x 88 x 91. Similar in other gas stations in neighboring areas that I've done road trips too.

Obviously in other places like California, its more driven by state law.

[Lenny_RDM]

Originally Posted by Coi

There is no law in California limiting octane. Some gas stations here sell 100 or even 103 AKI. What the laws do limit are certain additives that can be used to increase the octane rating of gasoline due to their harmful environmental or health effects.

California's premium gas originally went to down 91 when the state banned MTBE due to it polluting the water supply including drinking water. It may also be carcinogenic. Since then most other states have followed suit but companies supplying gas to CA never had a reason to make new formulations to increase the maximum octane again. The most common additive currently used to increase the octane in the US ethanol. CA limits ethanol percentage in regular gas to 10% (E10) while some states allow up to E15 to be sold as gasoline.

There are old patents that would allow for a 92 octane California-legal gas but no one wants to pay the licensing fee.

Health effects?!

[freshxdough]

Originally Posted by Drothgeb

I see you're a tech, so I'm wondering why lower octane fuel causes rough running when cold. It ignites and burns quicker than higher octane, so I would have guessed it to be better for cold starts.

From responses, it seems design spec is for 91. Can it automatically adjust the tune to take advantage of 93 or higher?

You simply explained it right there. It burns quicker. Lower octane fuel can ignite sooner than it's supposed to be. A combustion cycle is a finely tuned Swiss watch. It needs to fire the plug at the right moment to create a good smooth idle, especially at cold start when the engine is running at predefined parameters to get the engine up to an operating temperature as soon as possible Both due to emissions and due to controlling the engine with the 02 sensors once they heat up. If there is preignition in the cylinder while the piston is still traveling up, then it can result it pinging and rough running.

And the DME will monitor knock values to fine tune ignition. It knows what fuel you've put it, 87, 89, 91/93. That is why you can use 89 as minimum. Controlling timing is the way they can operate with different fuel safely and while still in control.