Can I use 100 octane?

[d_dot]

in the new m3 e92 can i fill up with 100 octane unleaded fuel or do i have to do a certain mix?

[davedave]

yes, u can use 100 octane. it doesn't hurts. If you want to get full benefit out of the 100 oct, you have to advance the timing

[d_dot]

Originally Posted by davedave

yes, u can use 100 octane. it doesn't hurts. If you want to get full benefit out of the 100 oct, you have to advance the timing

how do i do this with an ecu tune?

[davedave]

Get a custom ECU map road tune / dyno tune with your tuner.

[Lemans_Blue_M]

Originally Posted by d_dot

in the new m3 e92 can i fill up with 100 octane unleaded fuel or do i have to do a certain mix?

You can use 100 octane unleaded fuel without mixing it with anything else.

That's the good news...

The bad news is...

That's going to be very very expensive, and the power increase you get will be limited by the factory ECU programming.

The stock software will be able to adapt to a higher fuel octane rating of about 96. The S65 won't make any more power past that octane number, since the fixed ECU adaptation range will not allow it to adjust that far away from the factory software tuning.

The stock tuning is designed to operate on 93 octane unleaded gasoline.(US) There is a small window where the ECU can adapt to a lower octane rated fuel (90-91) and a higher octane fuel (95-96).

Anything outside of this limited range, will exceed the capabilities of the stock ECU's tuning parameters. So you won't get the full benefit of the 100 octane race gas.

If you want to use a higher octane fuel, and you also want to extract every bit of power you muster out of it...that would require a specific re-tuning of the ECU to make that happen.

And if you you do that...then you can't use the lower octane 93 fuel anymore...

[d_dot]

ok. but im not doing this as a permanent solution just a once in a blue moon type of thing. my ecu has already been retuned by AA for 93. so if i fill it up today with 100 will i feel a difference since it is programmed for 93?

[sparkyg]

There are dynos with 100 Octane and they do give you a bump and you will feel it.

Its not a kick in the ass but you'll feel it.

Do a and prob will find the dyno

Try pencilgeek,s resources too

[J08M3]

Originally Posted by Lemans_Blue_M

The stock software will be able to adapt to a higher fuel octane rating of about 96. The S65 won't make any more power past that octane number, since the fixed ECU adaptation range will not allow it to adjust that far away from the factory software tuning.

The stock tuning is designed to operate on 93 octane unleaded gasoline.(US) There is a small window where the ECU can adapt to a lower octane rated fuel (90-91) and a higher octane fuel (95-96).

Where do you get this info from?? PG got a big gain from 100 octane. How do you know what size window the software will adapt too with timing??

[Lemans_Blue_M]

Originally Posted by d_dot

ok. but im not doing this as a permanent solution just a once in a blue moon type of thing. my ecu has already been retuned by AA for 93. so if i fill it up today with 100 will i feel a difference since it is programmed for 93?

Yes, like I said before, the factory ECU engine programming that BMW has written will compensate for a higher octane fuel. (within a small range)

It just won't extract the maximum power from the 100 octane race gas, because it simply can't adapt that far from it's baseline tuning parameters.

Also...

Let me dispel a widely held (and fundamentally incorrect assumption) that many people seem to have about 'aftermarket performance tuning upgrades':

The factory ECU tuners like AA (or anyone else) do not write an entirely new engine management software program from scratch.

They simply MODIFY the existing factory ECU code, to manipulate a particular set of parameters. (or turn off certain CEL warning triggers) This allows them to achieve certain performance goals.

You would be surprised at how many people don't really understand that's all they really do. It's not an entirely different software program, but rather a 'hot rodded' version of the stock factory ECU code.

That's a good thing too...

Because the ECU still maintains all of it's original flexibility...like adapting to different fuel octanes within a preset range.

Aftermarket performance software providers can also manipulate this code as well, but not unless you specifically request it.

[Lemans_Blue_M]

Originally Posted by J08M3

Where do you get this info from?? PG got a big gain from 100 octane. How do you know what size window the software will adapt too with timing??

BMW engineers in Munich.

If you need confirmation, ask any well known aftermarket BMW factory ECU tuners in the United States, and they will verify this.

By the way...I never said it wouldn't make any power, what I said was the power gains on 100 octane fuel are CAPPED due to the restrictive nature of the engine managements tuning software.

BMW has no reason (as an OEM manufacturer) to spend millions of dollars perfecting a software program that adapts for fuel that should never be used in the car in the first place. They are not going to bare that added expense for no good reason. So the engineers map out a realistic octane performance window, and the write the software code to work within these limits.

The tuning windows are not very wide for a very good reason. The wider you make the fuel octane adaptation parameters, the more elaborate the programing has to be to compensate for all the other considerations. (air density, timing, etc) It can get to be a nightmare, if you have to write code to cover all possible engine conditions that may occur.

And the compression ratio of the engine itself, will also make this a dangerous proposition. (detonation and pre-ignition concerns with lower octane fuels)

[lucid]

PG, did you dyno test your engine at 96 octane? I don't remember if you did or not, but I know you did with 100 octane. The issue is if there are no other datapoints between 91/93 and 100 on the same engine, we can't know if there is a cap at 96 octane or not. If we have those data, then I guess they will speak for themselves...

[Lemans_Blue_M]

Originally Posted by PencilGeek

This sounds like the same exact discussion that happened a year ago on this board. In that thread, a poster was saying the same exact thing, with same exact contacts and information from BMW engineers -- with almost the same exact claims for 100 octane gas. Except in that thread, the poster said 100 octane wouldn't give ANY benefit. Then to prove him wrong, I ran the 100 octane dyno runs (See "Dyno Runs" in my signature below).

Now the story is only slightly different than before. The old story had octane maxing out at 93, but today's story says that it maxes out at 96. Other than that, the details seem absolutely identical.

I'm really wondering if you're the same guy. I'm tempted to look it up.

No idea who or what you are talking about in regards to this topic.

The stock tuning can adapt to a higher AKI index unleaded fuel. I thought I stated that clearly in my earlier posts. At no point did I infer that the use of such a fuel would not yield higher HP/TRQ numbers.

My point was that it would limit the power increase of the higher octane fuel.

Here is what I know...

If you drained your fuel tank, and used only 100 AKI unleaded gasoline, the stock ECU timing would not compensate for the higher octane fuel to achieve that maximum horsepower and torque available.

To achieve that specific goal, you would need a highly trained BMW ECU software tuner (with a stock ECU code disassembler) that could overwrite new code. That code would essentially 'trick' the car into thinking it was still running 93 AKI octane gasoline. This altered code could then maximize the gains of the better fuel. (while maintaining similar AFR's)

You guys are crazy if you think BMW would spend the time, money, and resources, to design an engine management software program that can adapt to any fuel you throw into the tank. The MSS60 ECU is advanced... but it's not a blade type main-frame computer...

[Lemans_Blue_M]

Originally Posted by PencilGeek

Actually, that discussion isn't interesting to me. I dont' think there's an issue at all -- there's only a curiosity and a desire to figure things out.



About a year ago, this same discussion came up. A poster came to the discussion and said he knew the BMW engineers who designed the ECU software for the new M3. According to that guy -- which was supposedly according to his friend at BMW -- the MSS60 would not adapt beyond about 93 octane. I was very doubtful because I am also a firmware designer by trade, and I said if I were BMW, I'd design the software quite a bit differently. I'll explain what I mean below in response to another one of your points.

To me there's very many parallels in that older thread and this one, that's why I wondered if you were the same guy. But if you're drawing a blank, then it's probably just a coincidence.



I know from past experience that a motor with 12.5:1 compression ratio needs about 103 octane fuel to run without detonation and maintain proper spark advance. It only goes to reason that a motor with 12:1 compression ratio needs about 100 octane fuel to run at optimum spark advance. If I were BMW (or any other ECU tuner), I'd design the ECU to run at optimum spark advance assuming the optimum fuel. Then I'd use the detonation detection to retard the spark advance until the detonation ceased. This has the benefit of not being bracketed by any fuel -- and guarantees the motor runs at the best performance regardless of the fuel being used. Best of all, this doesn't require " blade type main-frame computer" to do it. This is exactly how the first ECUs worked in the mid 1980's. If they changed from this type of fundamental design, why? What's the advantage to making the ECU's less flexible than they were 20+ years ago?

I'm willing to admit that I may be 100% wrong about this because in reality I don't know what BMW did in the ECU and I won't pretend that I do. Yet the designs being discussed in this thread and the thread that preceeded it just don't make sense to me. So maybe you can explain the benefit to bracketing ECU performance to certain octane ratings instead of making the whole thing dynamic and optimized regardless of octane rating?

EDIT:
I guess another way to look at it is like this. How does the ECU even know anything about octane rating? I suppose you're saying that the ECU doesn't have the bandwidth to dynamically adjust the spark in such a wide range as would be required. Why doesn't it -- they did 20 years ago?

Every BMW engine is dyno tuned in-house to a baseline map using the appropriate fuel for that engine compression. (in early development)

All BMW engines are then categorized into groups, and the most advantageous fuel is selected for further testing. A standard 3-series naturally aspirated 3.0 liter engine is baseline tested with the equivalent of our 89 octane fuel. That's the recommended minimum AKI octane rating for that category. So their dyno-tuning's SCOPE is based off that number.

The software tuning parameters are restricted on purpose, becuase BMW AG wants to minimize warranty claims and service appointments that are going to come out of their own pockets. They narrowly tune each engine to achieve a pre-set HP/TRQ goal, and then they work within those limits to compensate for a variety of outside influences. (including small shifts in octane ratings)

The base code adaptation range is not very wide at all.

All of this OEM ECU software coding is also heavily encrypted by the software engineers, to keep outside tuners from altering the base code. It doesn't usually work, but they still try to slow this stuff down as much as possible.

At the end of the day, you can use what ever octane rating you want when you pull up to your local gas station. The fact is the ECU will adapt the best it can to keep the engine from running too lean or too rich. The new generation of ECU's are good at doing that, but they are not designed to compensate for drastic changes in fuel octane rating as you seem to think.

BMW is a OEM manufacturer. They could care less if you want to fill up with 100 octane race gas on the weekends so you can hit the drag strip.

They are not going to spend one cent on tuning the ECU to properly adapt to that fuel octane rating, when they spent millions of dollars over several years trying to dial in the performance based on 93 (US) octane fuel.

The scope of their programming is set to create very good power output, balanced with the best fuel economy possible.

In their mind, you need to use the fuel they recommend, or you are on your own. (warranty wise)

Also...

Keep in mind that max power output is only made on a properly maintained engine.

BMW has to 'assume' that this will not always be the case. (again they are OEM) So the tuning must ADAPT to a variety of different circumstances including a dirty air filters, fouling spark plugs, clogged or partially restricted fuel filters, poor gas quality (regardless of octane), or even a mechanical malfunction to a key sensor. That's is where they pour the vast majority of their engineering resources. That alone requires a lot of computing power.

I can promise you that BMW could care less about programming the car to achieve ideal HP/TRQ for 100 octane fuel.

And and far as compression ratios go, engines have been running 12:1 compression on 91 octane gasoline for quite some time now. This pre-dates any new advances engine computer software programming, or the 'nanny sensors' used to detect knock. (detonation)

I'm sure some engines out there may require a higher octane rating, but that would depend on several factors including head design, fuel delivery system, and spark/coil technology used.

The stock ECU cannot work miracles. The tuning engine management software is purposely written to cover a smaller swing in octane rating to keep the overall file size to an absolute minimum. If they were to expand that range to cover a larger spread in fuel octane values, new tables would have to be written in to the base code, and a lot more engine dyno tuning would have to be performed to insure the engine's AFR's would remain in a safe range under any operating conditions.

Higher octane fuel are great for making power, but they also carry a higher risk if anything goes awry. The margin for error is smaller, than a lower AKI indexed fuel. That would simply tax the engineering resources to much to spend all that time and money for a fuel that should never be used in the engine anyway. (even if it makes more power)

These are the hard decisions you have to make as an OEM supplier.

Performance rarely dictates company policy in regards to what engineering path to take. It almost always comes down to cost and risk management.

[lucid]

Originally Posted by PencilGeek

Actually, that discussion isn't interesting to me. I dont' think there's an issue at all -- there's only a curiosity and a desire to figure things out.

Well, if the octane adjustment range the stock programming allows for stops at 96 octane as claimed by Lemans_Blue_M, then dyno runs done with 96 and 100 octane should not show any difference at all, and I thought that was the question under consideration here--wheater going up 100 yields any additional benefit or not as compared to 96. How else would you find out? And, by "issue", I mean "question".

[J08M3]

Originally Posted by lucid

Well, if the octane adjustment range the stock programming allows for stops at 96 octane as claimed by Lemans_Blue_M, then dyno runs done with 96 and 100 octane should not show any difference at all, and I thought that was the question under consideration here--wheater going up 100 yields any additional benefit or not as compared to 96. How else would you find out? And, by "issue", I mean "question".

Not exactly true. You will still get more HP with the same timing on higher octane gas because of the slower burn.

[lucid]

Originally Posted by J08M3

Not exactly true. You will still get more HP with the same timing on higher octane gas because of the slower burn.

Yes, you mentioned this before. What is the magnitude of that effect exactly? Any references? If its magnitude can be predicted/capped, it can be accounted for in a 96 vs 100 test, provided several datapoints are obtained since the overall effect will be small.

[J08M3]

Originally Posted by lucid

Yes, you mentioned this before. What is the magnitude of that effect exactly? Any references? If its magnitude can be predicted/capped, it can be accounted for in a 96 vs 100 test, provided several datapoints are obtained since the overall effect will be small.

To be honest I have no idea how measurable it would be between 96 and 100 octane. I know 100 will burn slower and the theory is it will produce power for a longer duration of the power stroke, but I've never tried to measure it. So I am unsure if it can account for a big, small, or no gain. But in theory there should be some amount of gain.

[SCCAForums.com]

Ok... I'll throw 'one' wrench in everyone's story... Although... this was for my '06 V10 M5 w/ RPI Tuning... but that car 'ONLY' liked 91 Octane... I tried 'mixing' 100 / 91... and even running straight 91 octane... car always ran quickest at the drags w/ 91 octane... and dynoed the most HP on 91.

Too me it made no sense... since it's 12:1 also... but I do plan to back up others who have said 100 Octane gives the M3 more HP... I've heard people post as much as 20 or 30... I'd be surprised if it was even 10. But can't wait!
Dave

[mixja]

Originally Posted by J08M3

To be honest I have no idea how measurable it would be between 96 and 100 octane. I know 100 will burn slower and the theory is it will produce power for a longer duration of the power stroke, but I've never tried to measure it. So I am unsure if it can account for a big, small, or no gain. But in theory there should be some amount of gain.

Originally Posted by J08M3

Not exactly true. You will still get more HP with the same timing on higher octane gas because of the slower burn.

I disagree - not in line with my thinking, which is if you are running 96 Octane and 100 Octane fuel and the ECU is advancing timing by the same amount, then both fuels are being burnt for the same time - your comment about "slower burn" doesn't mean it will burn longer, the timing dictates how long the fuel can burn for.

In fact given the 100 Octane burns slower, I'd suggest less chemical energy will be extracted meaning less power is made. I've seen this when I used to self tune an Autronic ECU in a Subaru STI I used to own. If I ran the same fuel/timing map (in the case of an Autronic it was a static timing map), the higher octane fuel would make less power and run richer.

Of course the higher octane fuel made more power once you increased timing and adjusted the fuel map, but in the scenario you are painting above (same timing, same fueling), higher octane fuel will make less power. Higher octane fuel will also run richer if you use the same fueling map, so you not only need to adjust timing, you also need to adjust fuel maps to get the most out of higher octane fuel.

[J08M3]

Originally Posted by mixja

I disagree - not in line with my thinking, which is if you are running 96 Octane and 100 Octane fuel and the ECU is advancing timing by the same amount, then both fuels are being burnt for the same time - your comment about "slower burn" doesn't mean it will burn longer, the timing dictates how long the fuel can burn for.

It does in fact burn slower/longer. The reason this creates more power is because most fuel is burnt immediately when the spark ignites it. It is done burning before the piston reaches the bottom of it's power stroke, therefore power is only being produced for part of the power stroke which only during the time the fuel is burning and the gases are expanding. A higher octane fuel will burn slower and therefore burn for a longer period of the power stroke.

[SCCAForums.com]

You guys honestly need to spend some time talking with a 'REAL' Race Fuel engineer... I've been Road Racing & Autocrossing for the past 20 years... And in that time, got to spend a lot of time with the head engineer for Unocals Race Fuel (now that BP took them over... they went and marketed their own product called 'Rocket Fuels' or something like that... it's been a while).

While it is commonly believed that the higher the octane, the slower the burn... that is not the case... the higher the octane number... is the higher resistance to pre-ignition... but the 'burn rate' is actually much faster, also sparking more HP...

The gentleman who was the head engineer had shared with me... that his 118 Octane actually burned significantly faster than their 110 etc...

So... please don't just assume higher number = slower burn.

Peace,
Dave

[dcstep]

I'm glad PG jumped in here with some facts. There's was lots of misleading conjecture prior to his entry into the thread. To the OP, yes, use 100-octane for "special" occasions and you'll be very happy there at sea level.

The discussion went beyond the OP's request and got into the impact of slower burning, high octane fuel and reaching the limits of the ECU. My E92 M3 lives at 5400-feet above sea level and I regularly use a dyno and high octane gasoline and mixes here in Colorado. I've tried 105-octane, 100-octane, 96-octane blend, 94-octane blend and straight 91-octane. Making a long story short, my car makes the most hp using 94-octane. It loses power with 105-octane unleaded, makes about the same power with both 91-octane and 100-octane, makes a little more with 96-octane and a little more than that with a 70/30 mix of 91/100-octane, approximating 94-octane.

My effective compression is significantly lower than those of you at sea level because of the low air density. My experiments would be kind of like putting 110 and 115-octane in our cars at sea level. I think that we can predict the answer, those higher octanes would probably generate no more hp and might actually start losing hp due to the "slower burning" ignition resistant nature of fuel actually screwing up the timing.

I'd love to see someone expand PGs experiment and try 105/100/96 octane in a stock car at sea level. The sweet spot may indeed be below 100-octane. (I'd be overjoyed with 30+hp, since at altitude we're only talking about around 6-hp at my altitude, even with the optimal blend). Don't give us the BS about what some unnamed engineer in Munich says. Let's just go to the dyno and get a "real" answer. Knowing the answer ain't rocket science, since it's easy to see at the dyno.

BTW, 36-hp is a 10% increase over SAE net at the rear wheels for most stock M3s. That's incredibly cheap hp. There's no reason not to try it. The car does fine.

Dave