93 plus octane no different than 91 when temps at 50-60 degrees?

[Ateam]

So as many of you all that is available at pump is 91 for me. I had been mixing 100 octane (5 gallons) in to achieve 93.8 roughly octane and really noticed a difference in the summer months of 105 degrees or even 80 degrees between the mix and regular 91 as far as pulling power.

Now that the temps are in the 50-60 range, I do not notice a difference in 91 or the mix of 93.8.

I am wondering if the outside temps being in this range or cooler is low enough to keep the air and engine cool enough to realize pretty much full sprak advance and less detonation compared to blistering hot weather?

Good news is do not need to pay extra for a few months. Costs about 23 extra dollars per tank to mix but still nice to save about 100 a month not having to do this!

[HT1000]

Of course cooler temps lower the combustion temp and reduce the possibility of detonation.

[rdollie]

Isn't the minimal requirement 91 octane for the M? I'm assuming you're stuck in California with their crappy 91 octane gas as the best available? When I lived there I used to buy 5-gallon cans of toluene (which is around 114 octane as I recall) and made my own gas blend BUT that was for a turbo car for track events. Unless you're going to the track or a serious street racer (by which I mean one who lines up against someone else and indulges in license/wallet/life risking speeds) I can't imagine bothering to make a 91+ blend for a naturally aspirated M.

In your case I believe your particular observation probably has much to do with winter formulation gasoline blends (probably the RVP variance but I need to think a bit more about the factors) in addition to lower temps (denser air meaning better fuel burn.)

[LarThaL]

Originally Posted by Ateam

So as many of you all that is available at pump is 91 for me. I had been mixing 100 octane (5 gallons) in to achieve 93.8 roughly octane and really noticed a difference in the summer months of 105 degrees or even 80 degrees between the mix and regular 91 as far as pulling power.

Now that the temps are in the 50-60 range, I do not notice a difference in 91 or the mix of 93.8.

I am wondering if the outside temps being in this range or cooler is low enough to keep the air and engine cool enough to realize pretty much full sprak advance and less detonation compared to blistering hot weather?

Good news is do not need to pay extra for a few months. Costs about 23 extra dollars per tank to mix but still nice to save about 100 a month not having to do this!

Very interesting topic. This is really dependent on the programming of the ECU. In a high revving, maximally tuned street engine like the M3 has, especially at higher rpms were cylinder filling/emptying times and ignition spark times are being squeezed, I am not suprised that colder denser air makes more of a difference than higher octane. To get a better understanding into this you also need to understand the physical and chemical properties of gasoline configurations, and specifically the octane molecular configuration. Too much to go into here, but do a general search. Interesting stuff.

[Ateam]

Oh I am sure the actual physics behind it all is wayyy over my head. I get the basics of how things work with timing, detonation, octane, intake temps, denser cold air etc etc but I do not know a lot of the intricies.

I would not normally do it if it was a big hassle to mix but a gas station down the street happens to stock VP 100 5 gallon drums and they are 49 bucks. So compared to regular pump gas at 3-4 bucks a gallon, which would be 20 bucks for 5 gallons, 29 dollars more per fill is not a big deal to actually get the 94 octane the rest of the country has access to! I would not do it if I did not notice a clear difference either but like I said now the cooler weather is not exploiting any noticable difference and thus not worth it.

In 110 degrees definetly a hue difference as the extreme heat must really retard the ignition timing in general.

[Dave07997S]

Originally Posted by rdollie

Isn't the minimal requirement 91 octane for the M? I'm assuming you're stuck in California with their crappy 91 octane gas as the best available? When I lived there I used to buy 5-gallon cans of toluene (which is around 114 octane as I recall) and made my own gas blend BUT that was for a turbo car for track events. Unless you're going to the track or a serious street racer (by which I mean one who lines up against someone else and indulges in license/wallet/life risking speeds) I can't imagine bothering to make a 91+ blend for a naturally aspirated M.

In your case I believe your particular observation probably has much to do with winter formulation gasoline blends (probably the RVP variance but I need to think a bit more about the factors) in addition to lower temps (denser air meaning better fuel burn.)

The M's 414hp is a rating that is achieved with 93 octane, 91 octane is the minimum for safe operating. Although the car is equipped with knock sensors and if a lower quality of gas is used the car can adapt.

Dave

[Ateam]

Originally Posted by Dave07997S

The M's 414hp is a rating that is achieved with 93 octane, 91 octane is the minimum for safe operating. Although the car is equipped with knock sensors and if a lower quality of gas is used the car can adapt.

Dave

Nothing to do with safe operating. Car will run as safely on 87 octane but will just continue to cut power. 91 is the lowest reccomended to still make within the ballpark of the rated hp, albeit will be less than 93. 87 you will start to signifigantly cut power and bmw does not want its m3 rated at 414 to feel like a slug by only having the engine output be 350 crank hp or less. But car can retard and run safely on almost any available octane

[BMRLVR]

I would answer your question however last time I did that you didn't think the answer was good enough...... Just like you didn't think Dave07997S's answer above was good enough.

In the future, if you want to ask a question do it and say thank-you when you get an answer. If you can't do that, don't ask anymore questions!


Ah shit, I will give you an answer anyway...... The benefit of 93 is going to be less noticeable as the weather gets colder however it will still net you some power even at 50-60 degrees. The S65 always seems to be pulling timing on anything below 98-100 octane in normal 80-90 degrees temps. I would venture a guess that you would have to get down below freezing before 93 would not require the DME to pull timing. I can not give you definitive octane, temperature numbers that will give you no timing retard however I can guarantee that the 93 is requiring the DME to pull timing at 50-60 degrees.

One sure-fire way to tell what octane/temperature will yield no timing retard would be to datalog the actual timing with different octane numbers in the tank at different temperatures. Beyond doing that, there would be no definite way to be precise.

[Ateam]

Originally Posted by BMRLVR

I would answer your question however last time I did that you didn't think the answer was good enough...... Just like you didn't think Dave07997S's answer above was good enough.

In the future, if you want to ask a question do it and say thank-you when you get an answer. If you can't do that, don't ask anymore questions!


Ah shit, I will give you an answer anyway...... The benefit of 93 is going to be less noticeable as the weather gets colder however it will still net you some power even at 50-60 degrees. The S65 always seems to be pulling timing on anything below 98-100 octane in normal 80-90 degrees temps. I would venture a guess that you would have to get down below freezing before 93 would not require the DME to pull timing. I can not give you definitive octane, temperature numbers that will give you no timing retard however I can guarantee that the 93 is requiring the DME to pull timing at 50-60 degrees.

One sure-fire way to tell what octane/temperature will yield no timing retard would be to datalog the actual timing with different octane numbers in the tank at different temperatures. Beyond doing that, there would be no definite way to be precise.

Why do you have to read my thread if you have nothing nice to say about me. That is some trend that everyone who seems to comment on what a troll I am, seem to read all my threads and post on them.

You gave an answer regarding the headers which did not address the actual question which was how the change/increase in flow and design of the tubing helped things in this application. You addressed the physical differences but not how that was going to translate into power.

As far as Dave above, I appreciate his input and do not disagree with anything except to clarify 87 octane will not damage an engine but rather pulling tons of timing. If I can't clarify or correct someone without being told it is some problem than what is the point of a forum. Some people read the net and take it for fact. I don't want someone thinking you are damaging your engine if you happen to run 87 once or all the time. Not sure many people do but might as well provide accurate info. I atlaest try to be accurate as much as possible.

I appreciate your response and did not know it pulls timing even wtih 98 octane. Sounds like we need full race gas all the time to get the most out of this engine which is not practical for 99 percent of us. Too bad as I always like to get the most power out of an engine that is built.

[BMRLVR]

Originally Posted by Ateam

Why do you have to read my thread if you have nothing nice to say about me. That is some trend that everyone who seems to comment on what a troll I am, seem to read all my threads and post on them.

You gave an answer regarding the headers which did not address the actual question which was how the change/increase in flow and design of the tubing helped things in this application. You addressed the physical differences but not how that was going to translate into power.

As far as Dave above, I appreciate his input and do not disagree with anything except to clarify 87 octane will not damage an engine but rather pulling tons of timing. If I can't clarify or correct someone without being told it is some problem than what is the point of a forum. Some people read the net and take it for fact. I don't want someone thinking you are damaging your engine if you happen to run 87 once or all the time. Not sure many people do but might as well provide accurate info. I atlaest try to be accurate as much as possible.

I appreciate your response and did not know it pulls timing even wtih 98 octane. Sounds like we need full race gas all the time to get the most out of this engine which is not practical for 99 percent of us. Too bad as I always like to get the most power out of an engine that is built.

What I told you about the header design was basically all there is to header tuning on a cross plane V8 engine with equal length design....... Primary length, primary diameter, merge collector design, and merge collector diameter. There is no simple explanation on what will work, there is just trial, error and dyno time while playing with the diameters and lengths of the primaries and merge collectors. You must also realize that 24 Motorsports probably made half a dozen different designs before they settled on the final combination that they are developing now.

I am always happy to answer any question and I will never give you false information. I am a mechanic for a living and a gearhead at heart and will never give an answer to a question that I don't now..... In the case I don't know, I won't post a reply.

[BMW&me]

While the ECU can retard the timing up to a point, any detonation - which is what causes the ECU to retard the timing after detonation occurs, is bad for the engine. Thus don't use lower than 91 octane unless it's an emergency and 91 or 93 is unavailable. Don't drive the car hard with 87 octane to minimise the risk of detonation.