M-Series (M1, M3, M5, M6)General M-Series Discussion - If it does not fit into a more specific M Category above, please place it in here. In addition, previously archived M-Series discussion is located in this section.
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For breakin on all our cars that is all I allowed my family to put in...other then that, it is very good for your car to put in higher octane gas...whenever I have the money I put in premium although I dont have to (528i)
i think your supposed to put the same octane gas as your car's compression 9.1 compression is 91 octane and i think your car is like 10 something so 100 octane is best, that's what i'v heard
NO.... your engine's compression does not conicide with what octane you should use. First off... the best answer to what octane you should use... should be in the owners manual. Second, I would only use that grade of fuel. Because the higher octane you get the longer it takes for it to ignite, thus pushing your engine to further compress that fuel/air mixture untill the fuel ignites.
Higher octane = higher flash point = takes more compression to combust = more strain on moving parts = longevity complications.
Below is an explaination.
The different levels of octane in gasoline tell you how much fuel can be compressed before it ignites. Gas is comprised of crude oil.. then it goes to the refinery.. and then you get .. what they call hydrocarbon chains of different lengths... then its blended to form different types of fuels according to the length of the chain... such as butane... methan... and propane... and of course heptane (which is the secondary part of gasoline)... well I know I'm getting on a tangent.. but octane is just one of those lengths of crude oil.. it can be compressed to a very high ratio before it combusts... so if your running 93 octane... thats 93% octane and 7% heptane... and will combust at a given compression ratio... so thats why you need to use a certain gas in a certain engine... all is relative with compression and octane. A higher octane fuel though... will be able to compress to a higher ratio.. therfor making your engine run at a slightly higher compression so it can combust after it mixes with H2O.
Originally posted by 97alpineM3@Aug 9 2004, 08:47 PM NO.... your engine's compression does not conicide with what octane you should use. First off... the best answer to what octane you should use... should be in the owners manual. Second, I would only use that grade of fuel. Because the higher octane you get the longer it takes for it to ignite, thus pushing your engine to further compress that fuel/air mixture untill the fuel ignites.
Higher octane = higher flash point = takes more compression to combust = more strain on moving parts = longevity complications.
Below is an explaination.
The different levels of octane in gasoline tell you how much fuel can be compressed before it ignites. Gas is comprised of crude oil.. then it goes to the refinery.. and then you get .. what they call hydrocarbon chains of different lengths... then its blended to form different types of fuels according to the length of the chain... such as butane... methan... and propane... and of course heptane (which is the secondary part of gasoline)... well I know I'm getting on a tangent.. but octane is just one of those lengths of crude oil.. it can be compressed to a very high ratio before it combusts... so if your running 93 octane... thats 93% octane and 7% heptane... and will combust at a given compression ratio... so thats why you need to use a certain gas in a certain engine... all is relative with compression and octane. A higher octane fuel though... will be able to compress to a higher ratio.. therfor making your engine run at a slightly higher compression so it can combust after it mixes with H2O.
most of the time using premium only adds up between $1-2 more, and for the tiny bit performance, and the right to say "this baby takes premium, bitch", that is money well spent
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Originally posted by 97alpineM3@Aug 9 2004, 08:47 PM NO.... your engine's compression does not conicide with what octane you should use.
............all is relative with compression and octane.
I just wanted to clarify so no one jumps on me here... the first statment I made about how a compression ratio and octane do no coinside was meant to project that the numbers as in 9.1:1 comp. ratio is not equal to a octane of 91. (If that was the case I was be fishin around here for some 105 octane)
But in a different realm the compression does work directly towards what octane 'should' be used in the car.
BUT!!!!!!!! That is a correct statment only with a "STOCK" ECU. Due to the fuel mapping and timing.
If you alter the state of your computer... aka a "Shark Injector" for instance... you are changing the fuel map and throttle timing and such. That's why the "Injector" says the upgrade will work best/only with 93 octane. The software pushes more fuel at certain times... and that takes more or less compression per particle of unit of the fuel/air mixture. Thus changing (at certain times ) the amount of fuel/air in the combustion chamber. So at certain times to gain power it uses that extra space for improvment called more octane thus giving you more compression and then power.
Some say that adding more compression due to a higher flash point of octane is bad for the longevity of the engine.
This is only TRUE if you dont have a upgraded computer system. Because if you just add more octane to a normal fuel map you add compression at the wrong times and you put strain on the engine at the wrong times.
With a upgraded fuel map it pushed back the fuel map and allows you to start the power band earlier with a slightly more compressed combustion chamber. It also puts use to the extra octane in more appropriate locations on the fuel map.
Hope this helps...
Please correct me if I'm wrong...... (god I hope Jim C. doesnt read this... cause I'm just taking outside knowledge and building a big picture.. )
What you are referring to are burn rates. Higher octane has a slower burn rate then lower octane. The higher compession the engine the slower you want the burn rate. This avoids pinging, burnn't pistons etc. The s54 engine is 11.5:1 and requires 91+ although anything over 98-99 would be over kill and of no value. I am talking stock engine and software. The M does have learing software but is limited. It can adjust within a range for different gas. You will loose performanec with less then 91 but prob. will not damage the internals. Many think higher octane means more flamable but that really has nothing to do with octane ratings. Octane will not change the compression. You measure compression without the engine running. I agree with Alpine M3 for the most part. Compression is only measured at top dead center and will not vary. I understand the logic you are applying and it does apply to burning pistons, pinging etc. At all but TDC a valve is opening or closing that's why compression can olly be measure at TDC only. In an extreme circumstance if you use too low an octane, it will burn to fast, not allowing the piston to move down quick enough to reduce the load and blow a hole through the piston or cause other serious damage to the engine. In other words, don't use cheap, low octane gas in a very high compression engine.
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okay... so for example i have a 95M3 ... it's suppose to according to BMW take 91, with a confronti chip/shark.. will i see any noticebale gains.. will it eally remap my fuel curve?
From what i understand all that chips can reallistically do for a nat. asperated engine is take off the top speed gov and increase the rpm range limit. Even if it does raise my hp by 8 @ 8000rpm.. is it really worth it?
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