C's Bimmer

Guys - Take a look at the first post on this thread for times and the meet. I specified an actual lot to meet at, for the Palisades Mall.

pennetta

No problem, the 20th is only two weeks away anyway.
I know our cars will retard the timing for lower octane gas, but will it go the other way if you put in octane higher than whats specified? The higher the octane the more resistant it is to spontaneous combustion which is combustion caused by heat and compression not by the spark plug firing.

tuningtech

That is actually called detonation. That is why cars have knock sensors which are actually listening devices for the ECU It will not advance the timing for higher octane gas. It just becomes a more violent explosion and hence: more power!

The term spontaneous combustion is burning that may occur when heat generated by chemical changes within a substance becomes trapped inside the substance. The substance combines with oxygen in a chemical reaction called oxidation. Normally, the atmosphere absorbs heat produced during oxidation. But a substance may retain this heat if stored in a place with poor air circulation. The temperature of the substance then rises and oxidation speeds up, producing even more heat. This cycle continues until the substance ignites. Spontaneous combustion occurs most readily in large piles of coal, heaps of oily rags, and damp hay.

Maybe you were actually thinking of "spontaneous human combustion"?

pennetta

You are correct about spontaneous combustion, I misused the phrase. But higher octane gas does not provide higher energy in itself, it allows you to either advance the timing (more power) or raise the compression ratio (more power). Higher octane resists the tendency to ignite caused by heat and compression (hence my misuse of spontaneous combustion) so it allows more of both.
But my question was does the ECU go the other way, and you have answered it. Do you know that or are you guessing? If it doesn't then 100 or 110 octane will not do anything more for you.

tuningtech

What the ECU does is it lets the engine use the upper level of the parameters set in the ignition table and it can use those setting for a longer period of time through the rpm range because of the higher octane fuel and that is how it does make more power.

Whereas the ignition retarding range is much larger in the software as a protection device, that is considered retarding the timing when the car picks up knocking(detonation).

When the engine timing is at the maximum level for a longer period of time it is actually considered optimized timing considering the higher octane fuel used. If you look at a stock ECU dyno curve you will see the sporadic movement up and down as you are getting higher in the RPM range and that is the terrible ignition table that is set from the factory. I guess you can say it is a play on words but the engine is always using the maximum timing at some point of the engines rpm range but just not all of the time so it is not considered advanced timing. That time is increased tremendously when running higher octane fuel so you definitely gain power. PERIOD.

I hope this has answered your cynical question to me about whether I am knowledgeable about the subject or just guessing. I guess you can answer that now yourself. I am really looking forward to meeting you in person on the 20th.

FYI: For all of you that are putting 100 or 110 octane in your cars on the 20th here is what is the best combination for your fuel mix: 1/2 tank 93 octane and 1/2 tank 100 octane. If you use only 100 or 110 and your tank is empty you will lose power. Even the 110 octane is not worth putting in your car unless you have a race fuel program set up in your ECU. Plus the cost of it is really just throwing your money away with 110. Sorry C.

C's Bimmer

You already met Dave, Bruce. He was at the meet you had at your shop, earlier this summer.

And the 110 Octane makes a difference. Not sure what all the blabbering was about, but it doesn't sound right. JK!

535i rob

bruce you know i had to try the 110 octane after C told me about it

pennetta

I didn't really know who you are, so I'm not being cynical, and you shouldn't get insulted. Just a lot of people give an opinion and its not always fact (not maliciously). I think we are both saying the same thing: I'm saying from a physics standpoint I don't believe that higher octane fuel contains more energy, but it allows you to tune the engine for more performance so you can get more power if you or your ECU retunes and the higher octane allows a higher threshold against detonation. Is that correct? Thus my question of can the ECU go the other way. You seem to be saying that the ECU can sporatically increase performance above the stock 91 octane state of tune, so there are benefits.
The reason I asked the question was I just wanted to know if I should put 100 octane in my car.
Anyway Bruce, as Carlton mentioned we already met and I look forward to seeing you again on the twentieth.
By the way Bruce, do you remember if you were bigger than me?
Dave

tuningtech

If you had met me before then you would know who I am especially if you were at the meet at my shop.

Size doesn't matter and it never has mattered to me. Size is never the issue it is only about how skilled you are.

Yes Dave you should, without a doubt, with your Dinan software, run 100 octane and you can even go with a more pure mixture. You have an upgraded ignition map with that software. Stock software settings will not get the full benefit of the higher octane if it is not mixed with conventional premium unleaded.

Also I am not sure about the 91 tune that you are alluding too. I believe that is what they use in 91 octane states like CA and is not the universal tune in all BMW's. Interesting though.

pennetta

Thanks, see you in a couple of weeks.