[F30guy]

Are there any issues with doing this long term? Any idea on how much HP is lost running 89 rather than 91? (91 is the highest here in CA)

[Beek]

[John in VA]

Here's a recent "discussion" on the subject: https://www.bimmerfest.com/forums/sh....php?t=1292015

[Billfitz]

It's never caused a problem for me. When I got my 328 I tested it with two tanks of 89 and then two tanks of 91. There was no difference in acceleration or mileage. I went back to 89.

[blankito]

I just don't understand people who buy expensive cars, often spend thousands on accessories and mods but get cheap on gas rating...

Honestly, I would never go lower than 89 since that's what is required. They say they recommend 91 so I put 91... Since I got a JB4 I always use 94 when available and 91 when there is nothing else

I do not have any numbers regarding power or mileage, but on most cars I had, I could feel the car ran smoother with the recommenced grade. Also, unless you drive 3000 miles per month, the difference between 89 and 91 will be only a few dollars per month so why take a chance?

[Sirhc1115]

I strongly recommend you use the proper grade of fuel. If the car didn't need it then they wouldn't have it on there when there are other grades . Not using the proper grade can cause pre detonation and long term conditions of this can harm the car. Plus if the manual says to use 91 or higher and you don't it can potentially void a warranty claim if a problem does arise.

[anotheran]

Originally Posted by F30guy

Are there any issues with doing this long term? Any idea on how much HP is lost running 89 rather than 91? (91 is the highest here in CA)

BMW states that the minimum AKI Rating is 89 in their manual so the engine should be fine with that fuel. This is what BMW's manual states:

The minimum AKI Rating is 89.
If you use gasoline with this minimum AKI Rating,
the engine may produce knocking sounds
when starting at high outside temperatures.
This has no effect on the engine life

(I added the bolding for emphasis)

You'll probably lose 5-8hp using 89 compared to 91. But you'll probably feel the torque loss a lot more (somewhere in the range of 20-30 ft-lbs).

[IanW555]

Would be great if someone did some dyno testing on the different octanes available. Here in the UK the lowest is 95 octane, which I use, I often wonder whether the ECU would adjust up to make the most of the 98 octane available?

[Billfitz]

Originally Posted by blankito

I just don't understand people who buy expensive cars, often spend thousands on accessories and mods but get cheap on gas rating...

I don't understand people willing to pay a premium price for something based on nothing more than advertising claims. Never forget that truth in advertising is an oxymoron. When I see proof from 3rd party testing that contradicts my own testing results I'll consider paying more, after I conduct my own tests again. Until then I'll pocket the difference.

You'll probably lose 5-8hp using 89 compared to 91

Based on what? It's true that when the engine is pushed to its limits that there's a benefit to higher octane. I don't push my engine to its limits, and unless you're on the track I doubt that you do either. If you do you probably shouldn't.

[anotheran]

Originally Posted by Billfitz

Based on what? It's true that when the engine is pushed to its limits that there's a benefit to higher octane. I don't push my engine to its limits, and unless you're on the track I doubt that you do either. If you do you probably shouldn't.

Based on dynos using the same dyno manufacture and the same correction type between 91 and 93 octane that many ppl have done for base lining their JB4 tune. Op asked about hp difference so we're looking at top end and not really about practicality on the road.

Since you mentioned practicality here, the op can download the BMW M timer app and do some 0-60s between 89 octane and 91 octane and see what real life difference it makes.

not really here to preach higher octane is better, just giving the op all the info i know so he can make a decision.

[DarkStarBimmer]

It's a no brainer to put the best possible gas in the car you spent 40-70K on.

Knock/detonation is NOT your friend. Octane matters. It's scientific fact, not opinion.

Sure a stock powered car can probably get away with running 89, but that doesn't mean you should do it. You're running a forced induction engine, you don't want to be pinching pennies around the way it breathes and eats. Air and fuel.

You can probably get away with running your car a quart of oil low all the time, but that doesn't mean you should do it!

[insanecoder]

if you push the bimmer recklessly
and esp if you've got a tune on
you need to go higher octane

[bimmer456]

Running 89 should be fine on stock tune.

[chiefneil]

If you’re just tooling around town or commuting to work during rush hour, I don’t see how you’d notice the loss of a few hp from using 89 octane vs 91. Crazy fact: when you’re at partial throttle you’re not using every last bit of power your engine can deliver. That said, I did know one guy for whom every single drive involved a moral imperative to drive as fast as humanly possible and who drove a car with a gas pedal (and brakes) that apparently was completely binary - either full gas or none at all. If you’re like that guy, then yeah go with the 91 octane.

Regarding engine knock - yes it’s a bad thing. That’s why modern engines detect knock and adjust for it. Using 89 octane will not damage the engine.

Personally I just use 91 not due to any deep-seated desire to have all 300 lb-ft of torque available to me when I’m driving to the grocery store, but just because I don’t really give a crap either way and I can afford it. But I did used to care about saving a few bucks and used 89 octane in my E46 for about a decade with no ill-effects; except for road trips where I’d be blasting uphill through mountains with plenty of full throttle - then I’d spring for 91.

Do what floats your boat. Your engine will be fine. It’s more important to use a name-brand gas with good detergents, IMHO.

[kern417]

I get the desire for statistical data and tests but there's a point where you can just be realistic. Research doesn't trump common sense. And the fact of the matter is that these cars can accomodate a lot, including lower octane ratings, but you will see a degradation in performance. OEMs tune cars on higher octanes to improve efficiency and ratings across the board. So put in 89, let the car pull timing and adjust, and move on if you want to. But you're not really concerned about operating on the limit if you're putting in the minimum octane rating "until" you see hard evidence that something is being damaged.

I don't even argue with people that I know don't care about their cars. You hear people saying it's a lease, they'd rather save the money, etc. all the time. I'm just surprised to see it on an enthusiast forum. I may run the cheapest 93 that's a reasonable distance from my home/work, but i still will always run 93.

[Billfitz]

Originally Posted by DarkStarBimmer

It's a no brainer to put the best possible gas in the car you spent 40-70K on.

Define best. It's not synonymous with most expensive, or highest octane. Stock BMW four bangers just don't have high enough compression ratios or boost pressures or sufficiently advanced timing to gain any benefit from higher than 89 octane unless driven in track situations.

[DarkStarBimmer]

Originally Posted by Billfitz

Define best. It's not synonymous with most expensive, or highest octane. Stock BMW four bangers just don't have high enough compression ratios or boost pressures or sufficiently advanced timing to gain any benefit from higher than 89 octane unless driven in track situations.

You don't think a BMW four banger can spin bearings or throw rods?

[chiefneil]

Originally Posted by DarkStarBimmer

You don't think a BMW four banger can spin bearings or throw rods?

Ironically, that’s probably more likely to happen while running high octane and utilizing every bit of hp. Something somebody content to run on 89 octane is unlikely to be doing.

[BEAR-AvHistory]

Originally Posted by Billfitz

Define best. It's not synonymous with most expensive, or highest octane. Stock BMW four bangers just don't have high enough compression ratios or boost pressures or sufficiently advanced timing to gain any benefit from higher than 89 octane unless driven in track situations.

Not so, the 4 cylinders run more stock boost then the 335 MPPK. The 320 has the same compression ratio as the 440 MPPSK.

Basic tunes are running the 4 cylinder in the low 20's. 6 cylinder N54 hack was to use 4 cylinder parts to enable boost rates over 20psi.

If you have not dumped logs of the stock 4 cylinder engine how would you know what the the ignition advance curve looks like?

[Digital_83]

I cant remember a day when I put anything else below 93 ... including rentals

[blankito]

Originally Posted by Billfitz

I don't understand people willing to pay a premium price for something based on nothing more than advertising claims. Never forget that truth in advertising is an oxymoron. When I see proof from 3rd party testing that contradicts my own testing results I'll consider paying more, after I conduct my own tests again. Until then I'll pocket the difference.
Based on what? It's true that when the engine is pushed to its limits that there's a benefit to higher octane. I don't push my engine to its limits, and unless you're on the track I doubt that you do either. If you do you probably shouldn't.

Are you saying all the CHIP tuning are based on nothing? No matter the CHIP you use on your car (either Unitronic on a VW, JB4, MPPK), they all take into account the octane level in the gas to achieve specific performance and use dyno data to confirm their tuning.

Your stock BMW car is simply tuned to be used with 91 octane but is "okay" using 89. Another CHIP might be tuned for 93 octane, etc etc.

Another good example is the JB4 on map 5, which will detect the octane level in the gas and change the performance accordingly.

I completely agree that octane level means nothing on a Toyota Corolla that is designed to run over 87 octane. If you put 91 or 93, it won't help anything. However, putting lower than what the car is designed for, that's another story...

[tuco44]

I am in the camp that runs the octane rated gas that BMW recommends for my particular car. I use 91 and 94 (Chevron) exclusively.

This topic keeps coming up about every 2 months or so, and there are always those who run lesser octane rated gas than is recommended. And I always wonder why you own a vehicle with recommended 91, then run 89 or even 87. I just don't get it......I have to believe that BMW recommends 91 for a reason.......