Is regular unleaded better than super unleaded?
12-31-2005, 10:20 AM
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Originally Posted by SKK' post='217707' date='Dec 31 2005, 02:16 PM
I just wish I was paying what you yanks do for petrol. Screw the octane rating 
12-31-2005, 10:54 AM
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Originally Posted by ImolaRedM' post='217665' date='Dec 31 2005, 04:15 PM
Here's some good information.
http://www.stanford.edu/~bmoses/knock.html
Also, while I said tubo's don't need higher octane they're generally attached to engines with higher compression anyway. Remember that a turbo is just an air pump (like an engine). It will help your engine breath better. The turbo itself has little to do with the actual detonation of the air-fuel mix.
http://www.stanford.edu/~bmoses/knock.html
Also, while I said tubo's don't need higher octane they're generally attached to engines with higher compression anyway. Remember that a turbo is just an air pump (like an engine). It will help your engine breath better. The turbo itself has little to do with the actual detonation of the air-fuel mix.
12-31-2005, 03:39 PM
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My Ride: 2005 BMW 545i, Silver Grey, Sport Package, R. Shades, Cold Pkg, Sat. Rad., Prem. Sound.
Originally Posted by subterFUSE' post='217700' date='Dec 31 2005, 12:51 PM
Octane rating basically tells you how much pressure the fuel can withstand before combusting spontaneously. Higher octane = higher compression.
If the fuel combusts too early, then your engine will knock.
If you can use lower octane without engine knocking, then go for it.
Personally, I won't risk it. The price difference here in the USA isn't that much.
If the fuel combusts too early, then your engine will knock.
If you can use lower octane without engine knocking, then go for it.
Personally, I won't risk it. The price difference here in the USA isn't that much.
As for the bimmer, I think using the lower octane will not hurt your engine; you just don't get that much power out of it compared to using higher octane. If this goes true, and I fill up my 545i with jet fuel, then it should be faster than a 550i running 93 octane, right?
12-31-2005, 03:59 PM
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The label inside the fuel filler flap specifies 91-RON to 98-RON unleaded fuel. So I guess the standard unleaded in the UK (aka Premium Unleaded) at 95-RON is just fine. I still have no idea why the car feels *much* smoother with 95-RON fuel compared with Shell Optimax (98-RON).
12-31-2005, 04:01 PM
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Originally Posted by colejl' post='217718' date='Dec 31 2005, 02:54 PM
Quite the reverse, turbo-changed engines have lower cylinder compression! Normally aspirated engines have compression in the 10 to 11:1 range and turbo engines in 8 to 9:1 range... However, the amount of fuel and air in the combustion chamber is vastly increased because of the forced induction. The higher octane fuel can be ignited slightly later (avoiding pinking) than 'normal' octane and is usually more efficient.
12-31-2005, 04:12 PM
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Originally Posted by Bimmer32' post='217791' date='Dec 31 2005, 07:39 PM
So in layman's terms, lower octane burns faster than higher octane. In the past, I used premium (93) on my Camry and got better mileage than when I used the regular (87).
As for the bimmer, I think using the lower octane will not hurt your engine; you just don't get that much power out of it compared to using higher octane. If this goes true, and I fill up my 545i with jet fuel, then it should be faster than a 550i running 93 octane, right?
As for the bimmer, I think using the lower octane will not hurt your engine; you just don't get that much power out of it compared to using higher octane. If this goes true, and I fill up my 545i with jet fuel, then it should be faster than a 550i running 93 octane, right?
And yes, most modern cars (bimmers included) will do okay with lower than recommended octane fuel. But they won't put out as much power as with the fuel they were designed for. The engine mapping of the ECU or ignition system can compensate for the lower octane fuel by retarding the ignition. Thanks to the electronic engine management we all love and hate found in all cars since the mid 90's.
However, putting in 102 octane or 100LL (aviation fuel or whatever) into your car designed for 91 (or 87) octane will not give you any added boost. The engine wasn't made to take advantage of it. Shell, Exxon Mobile and the other gas companies would like to make you think it would but it won't unless you experience engine knocking. But that's not something you're going to see in the E60 for a LONG time (if ever).
01-01-2006, 12:24 AM
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So in layman's terms, lower octane burns faster than higher octane. In the past, I used premium (93) on my Camry and got better mileage than when I used the regular (87).
As for the bimmer, I think using the lower octane will not hurt your engine; you just don't get that much power out of it compared to using higher octane. If this goes true, and I fill up my 545i with jet fuel, then it should be faster than a 550i running 93 octane, right?
As for the bimmer, I think using the lower octane will not hurt your engine; you just don't get that much power out of it compared to using higher octane. If this goes true, and I fill up my 545i with jet fuel, then it should be faster than a 550i running 93 octane, right?
And yes, most modern cars (bimmers included) will do okay with lower than recommended octane fuel. But they won't put out as much power as with the fuel they were designed for. The engine mapping of the ECU or ignition system can compensate for the lower octane fuel by retarding the ignition. Thanks to the electronic engine management we all love and hate found in all cars since the mid 90's.
However, putting in 102 octane or 100LL (aviation fuel or whatever) into your car designed for 91 (or 87) octane will not give you any added boost. The engine wasn't made to take advantage of it. Shell, Exxon Mobile and the other gas companies would like to make you think it would but it won't unless you experience engine knocking. But that's not something you're going to see in the E60 for a LONG time (if ever).
[/quote]
Indeed - you get mixed results. Some people report increased power, smoothness and mpg others report the opposite or no change! There's obviously a pyschological effect too! (You just spent extra, it MUST be better
)Although some engines love it!
I'm currently using higher cetane diesel (BP Ultimate) and I think it's better...
01-01-2006, 04:04 AM
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I'm currently using higher cetane diesel (BP Ultimate) and I think it's better...
[/quote]
Interesting to hear someone else's opinion on this. I've also been using higher cetane diesel (also BP ultimate) in my 530d E61 for about three months with a definite improvement in smoothness when cold and a small increase in economy.
[/quote]
Interesting to hear someone else's opinion on this. I've also been using higher cetane diesel (also BP ultimate) in my 530d E61 for about three months with a definite improvement in smoothness when cold and a small increase in economy.
01-01-2006, 04:36 AM
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[/quote]
I haven't done any exact measurement of consumption because it's hard to match like-for-like driving on different fuels. But I agree it seems smoother and less emissions (smokiness).
01-01-2006, 07:43 AM
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the ecu senses the octane level of the fuel (by seeing how hard it is to combust the fuel... but thats technical talk)
bmw recommends you use ron98.. but the car is tested all teh way down to ron92...
I dont know about american cars but since the ecu has no map for lower than 92 octane fuel
i would not recommend you use it
bmw recommends you use ron98.. but the car is tested all teh way down to ron92...
I dont know about american cars but since the ecu has no map for lower than 92 octane fuel
i would not recommend you use it