Octane for 650iX

[BillCB]

This is for the engineers amongst us!

BMW recommends minimum 91 octane for their engines. I've always believed that there is no advantage in putting higher octane in the tank - but is this true?

I happened to put 93 octane in my tank today and it struck me the car seemed to perform a tad better. Of course this was strictly subjective, based on no formal test at all, but could it be so?

Opinions welcome!

[Tuesday]

I drove my old F02 750 cross country from Los Angeles to Manhattan and back - I always filled up with the highest grade available and without doubt they made a difference. Not only in performance, but economy as well.

[BMWMilan]

Originally Posted by BillCB

This is for the engineers amongst us!

BMW recommends minimum 91 octane for their engines. I've always believed that there is no advantage in putting higher octane in the tank - but is this true?

I happened to put 93 octane in my tank today and it struck me the car seemed to perform a tad better. Of course this was strictly subjective, based on no formal test at all, but could it be so?

Opinions welcome!

There is a difference when it comes to performance.

Is it necessary? Necessary like having oxygen to sustain life? No, it's not.

But if you're buying a lower grade simply because its cheaper, realize something. You just bought what was retail a 100k car. You're now concerned about a 10¢ difference in gas price. Say you fill up 5x a month, that works out to about $10 a month, or $120 a year. A rounding error in the grand scheme of things.

[neversummer78]

If you drive your car hard, then you will appreciate the higher octane gas. I was getting Drivetrain Malfunction error constantly driving with 91 octane. It was so bad that I can produce Drivetrain Malfunction error on demand. However, I want to drive my car the way it was meant to be, or I rather drive around in a Prius. Anyway, my engine was running rough, pinging, and misfiring which led to Drivetrain Malfunction error under load with low octane gas. I added octane booster to every tank now, and I no longer experience this problem. Also, engine is much more responsive because ECU is no longer adjusting ignition timing to lower octane gas which cause early detonation. Early detonation can be detected by knock sensor which causes ECU to adjust/dial-back ignition timing. This new BMW's twin turbo V8 is prone to early detonation, so ECU is preventing it from producing power at its full potential with lower efficiency when running on low octane gas. I can confirm that I get more miles per gallon with higher octane gas, so the saving on lower octane is not relevant with this engine. NA engines with low compression ratio are not running as hard/hot, so they cannot take advantage of higher octane gas anyway.

[agu845]

Originally Posted by neversummer78

If you drive your car hard, then you will appreciate the higher octane gas. I was getting Drivetrain Malfunction error constantly driving with 91 octane. It was so bad that I can produce Drivetrain Malfunction error on demand. However, I want to drive my car the way it was meant to be, or I rather drive around in a Prius. Anyway, my engine was running rough, pinging, and misfiring which led to Drivetrain Malfunction error under load with low octane gas. I added octane booster to every tank now, and I no longer experience this problem. Also, engine is much more responsive because ECU is no longer adjusting ignition timing to lower octane gas which cause early detonation. Early detonation can be detected by knock sensor which causes ECU to adjust/dial-back ignition timing. This new BMW's twin turbo V8 is prone to early detonation, so ECU is preventing it from producing power at its full potential with lower efficiency when running on low octane gas. I can confirm that I get more miles per gallon with higher octane gas, so the saving on lower octane is not relevant with this engine. NA engines with low compression ratio are not running as hard/hot, so they cannot take advantage of higher octane gas anyway.

this man know of what what he speaks (I read his other drivetrain malfunction thread with some trepidation as a new owner myself). fortunately we have 93 here. fingers crossed.

as for you, go premium

[Samurai of 2day]

I can side with everyone who has posted here so far. I have noticed that whenever I top off with 93 octane in my car, and even my bike, both machines perform much better. I ALWAYS use 93 octane in both of my toys now, and I have never gone for anything lower in over 8 years now.

As it was mentioned earlier, these vehicles were designed to put out power, and power needs to be fueled. so using the highest quality fuel usually equates to power being put out efficiently.

It is the same with all living things as well. The better quality fuel that is taken in, the better performance output is obvious. All athletes meticulously monitor the "fuel" they use, in order to maximize their performance in whatever sport or competition they choose. Engines and motors work the same way it seems.

[neversummer78]

Originally Posted by agu845

this man know of what what he speaks (I read his other drivetrain malfunction thread with some trepidation as a new owner myself). fortunately we have 93 here. fingers crossed.

as for you, go premium

Thank you

[BillCB]

Thanks everybody for your responses. I'll go with 93 whenever I can get it.

[gehmjc21]

What would be better, premium 93 or ethanol free 91?

[Bönz]

78 is correct. Octane is only a rating indicating a fuel's resistance to detonation. While modern engines can dial back spark advance, adjust fuel timing, valve timing and boost to mitigate pre-ignition (knock) there is no point in using lower octane fuel in an engine specifically designed to take advantage of higher octane. As ips said, are you trying to save a few cents? In the end this could cost you a boatload of engine trouble, especially on these V8's that seem to be very sensitive to fuel quality.

I believe BMW specifies 91 minimum, which would lead me to believe that the ECU can take advantage of even higher octane, like 93 (which I use in Michigan, although 93 is not available everywhere). I am sure this is only true to a point. You're not going to gain much more from 100 octane racing fuel.

Most every pump out there now has 10% ethanol. Our cars our built to handle this. I would still go for the higher octane.

On a related note, I have added my first bottle of Chevron Techron at about 12k miles. While I have never had the engine malfunction problems of other posters, I decided to give it a try based on all the favorable reports both in this forum and around the net. I must admit, it made a noticeable difference in my idle, especially with the AC compressor off when the idle falls to about 500rpm. I cannot attest to increased power or any other such claims, but certainly the Techron must have cleaned out the injectors to smooth the idle like it did. I will continue to use this product every 3000 miles or so. I am impressed.

Hey Southy: Can your dad get us all a bunch of coupons for this stuff?

[JNoSol]

The higher the octane, the more oxygen it can burn. Also, higher octane reduces the chances of pre-detonation on boosted and high compression engines. Of course, too high and you'll reach the point of diminishing performance. 93 is the highest I would go without a tune.

[southern6er22]

Originally Posted by Bnz

Hey Southy: Can your dad get us all a bunch of coupons for this stuff?

Haha. I'll see what I can do.

I use exclusively 93 - from Chevron.