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E34 (1989 - 1995)

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  #1  
Old 11-21-2012, 03:09 AM
wooferbmw wooferbmw is offline
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Octane rating

Good morning all!
I've read a lot about octane ratings for my 1990 m20 e34 and cannot find the simplest of answers. Can someone tell me what the octane rating is for a 1990 525i m20?
Thanks!
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  #2  
Old 11-21-2012, 05:54 AM
robertobaggio20 robertobaggio20 is offline
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You can use any kind of fuel on your E34. You are however only restricted to premium if you a running a chip that retards your timing...lower octane fuel would cook off under high compression and cause knocking in your engine, and i'm not sure if the M20 engine had any knock sensors in its cylinder head.
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  #3  
Old 11-21-2012, 05:03 PM
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Quote:
Originally Posted by wooferbmw View Post
can someone tell me what the octane rating is for a 1990 525i m20?
87
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  #4  
Old 11-22-2012, 06:53 AM
snowsled7 snowsled7 is offline
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Quote:
Originally Posted by robertobaggio20 View Post
You can use any kind of fuel on your E34. You are however only restricted to premium if you a running a chip that retards your timing...lower octane fuel would cook off under high compression and cause knocking in your engine, and i'm not sure if the M20 engine had any knock sensors in its cylinder head.
This is wrong in all kinds of ways. Lets see if the mods allow a correction to stand....

You should not use just any fuel. You should use what is reccomended.

The M20 is like the M30, lower in compression and they use 87 in stock form.

The performance chips advance the timing, creating more cylinder pressure and therefore require higher octane fuel to prevent pre-ignition.
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  #5  
Old 11-22-2012, 08:37 AM
robertobaggio20 robertobaggio20 is offline
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Originally Posted by snowsled7 View Post
This is wrong in all kinds of ways. Lets see if the mods allow a correction to stand....

You should not use just any fuel. You should use what is reccomended.

The M20 is like the M30, lower in compression and they use 87 in stock form.

The performance chips advance the timing, creating more cylinder pressure and therefore require higher octane fuel to prevent pre-ignition.
No they retard the timing. The spark is delayed (i.e. retarded i.e. held back) to allow the piston to compress the fuel/air mixture even further before it is cooked off. The greater the compression at the point of sparking, the greater the force generated from its combustion.

However, lower octane gasoline cannot handle these levels thus cannot function with chips which almost exclusively rely on higher f-a compression/retarded spark timing to generate better engine performance. Premium gasoline is always recommended.



rgds,
Roberto
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  #6  
Old 11-22-2012, 08:52 AM
snowsled7 snowsled7 is offline
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Originally Posted by robertobaggio20 View Post
No they retard the timing. The spark is delayed (i.e. retarded i.e. held back) to allow the piston to compress the fuel/air mixture even further before it is cooked off. The greater the compression at the point of sparking, the greater the force generated from its combustion.

However, lower octane gasoline cannot handle these levels thus cannot function with chips which almost exclusively rely on higher f-a compression/retarded spark timing to generate better engine performance. Premium gasoline is always recommended.



rgds,
Roberto

You need to go back to school on this.

You do not fire the plug later (retard timing) to build more cylinder pressure. Firing the plug sooner BTDC, to a point, creates more pressure, requiring higher octane to prevent a flash (knock). The fire is started sooner, that is what creates more pressure.

The compression ratio is static, no chip can change it, it is a mechanical relationship involving bore, stroke, pistons and head volume.

We need to add this to the archives proving bobby has no clue and, should stop giving advice until he gets one
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  #7  
Old 11-22-2012, 03:40 PM
paperplane94 paperplane94 is offline
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  #8  
Old 11-22-2012, 04:23 PM
robertobaggio20 robertobaggio20 is offline
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Quote:
Originally Posted by snowsled7 View Post
You need to go back to school on this.

You do not fire the plug later (retard timing) to build more cylinder pressure. Firing the plug sooner BTDC, to a point, creates more pressure, requiring higher octane to prevent a flash (knock). The fire is started sooner, that is what creates more pressure.

The compression ratio is static, no chip can change it, it is a mechanical relationship involving bore, stroke, pistons and head volume.

We need to add this to the archives proving bobby has no clue and, should stop giving advice until he gets one

Alright snowy I will read up on this again as your chain of causation seems plausible, at first blush.

However, do consider being more polite or at least not rude when pointing anyone's faults out. What does it profit a man to gain the whole world (i.e. be right about everything) but lose his soul (be a meanie) in the process ?
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  #9  
Old 11-22-2012, 04:39 PM
robertobaggio20 robertobaggio20 is offline
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Well Snowy my good man it appears that you're right after all !

http://rescomp.stanford.edu/~efroeh/...erformance.pdf

I stand advised, with thanks to Snowy.


rgds,
Roberto

p.s. IMEP stands for internal mean effective pressure.
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  #10  
Old 11-24-2012, 12:44 AM
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BMWFatherFigure BMWFatherFigure is offline
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By the way, back to the octane question - We run 98 over here. Our LOWEST is 91 and I would only use that in my lawn mower. I'm willing to be shown wrong but I thought that the ECM 'learntl' as it went along and will produce the best with whatever it is given.
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  #11  
Old 11-24-2012, 03:35 AM
robertobaggio20 robertobaggio20 is offline
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Originally Posted by BMWFatherFigure View Post
By the way, back to the octane question - We run 98 over here. Our LOWEST is 91 and I would only use that in my lawn mower. I'm willing to be shown wrong but I thought that the ECM 'learntl' as it went along and will produce the best with whatever it is given.
I don't think the cars of our era had octane sensors...
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  #12  
Old 11-24-2012, 05:18 AM
snowsled7 snowsled7 is offline
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Quote:
Originally Posted by BMWFatherFigure View Post
By the way, back to the octane question - We run 98 over here. Our LOWEST is 91 and I would only use that in my lawn mower. I'm willing to be shown wrong but I thought that the ECM 'learntl' as it went along and will produce the best with whatever it is given.
Octane ratings are listed differently in different parts of the world. In the US we generally use the RON + MON/2 and post the result.

Different parts of the country even sell different octane. Our lowest in the mountains is 85 octane. It powered my 535 just fine until I installed the chip.

Engines use knock sensors and adapt these days, that is correct. The M50 and M60 engines certinly have this function. Engine power and efficiency drop some on lower octane, but they will run on it.

The M20 and M30 engines had less capable ecu systems but were low enough in compression to run on low octane fuel. There is no advantage to running premium if the car isn't tuned to take advantage of it.
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  #13  
Old 11-24-2012, 05:02 PM
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supertech777 supertech777 is offline
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Quote:
Originally Posted by snowsled7 View Post
Octane ratings are listed differently in different parts of the world. In the US we generally use the RON + MON/2 and post the result.

Different parts of the country even sell different octane. Our lowest in the mountains is 85 octane. It powered my 535 just fine until I installed the chip.

Engines use knock sensors and adapt these days, that is correct. The M50 and M60 engines certinly have this function. Engine power and efficiency drop some on lower octane, but they will run on it.

The M20 and M30 engines had less capable ecu systems but were low enough in compression to run on low octane fuel. There is no advantage to running premium if the car isn't tuned to take advantage of it.
+1 on this , in my part of the woods the lowest rating is 87 and 93 being the highest . I run 93 since I have replaced my chip and does wonders for it ...

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  #14  
Old 11-24-2012, 11:48 PM
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BMWFatherFigure BMWFatherFigure is offline
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Maybe you have the same range of octane rated fuel but with different numbers. Our numbers are 'RON'. Could be it's like water freezing at either 32F or 0C. Same temperature, different way of measuring it. I run my older cars on 98 not so much for performance but to compensate (I hope) for no lead.
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  #15  
Old 11-25-2012, 07:26 AM
snowsled7 snowsled7 is offline
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Quote:
Originally Posted by BMWFatherFigure View Post
Maybe you have the same range of octane rated fuel but with different numbers. Our numbers are 'RON'. Could be it's like water freezing at either 32F or 0C. Same temperature, different way of measuring it. I run my older cars on 98 not so much for performance but to compensate (I hope) for no lead.
It certainly used to be that higher test fuels were availible outside the US, and it is probably so to this day.

I think you are right on when you say that we have the same range, just different labeling.

What our govt likes to do to screw things up these days is to put 10% ethanol into our gas lowering its energy content under the false pretense of cleaner air.
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  #16  
Old 11-26-2012, 01:31 AM
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BMWFatherFigure BMWFatherFigure is offline
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BTW did you realise that the British Clean Air Society (or what ever their correct name may be) WITHDREW it's support for unleaded petrol? Fat lot of good it did us. Of course they don't get photo-chemical smog. And another useless fact: Perth (my home town) is the smallest city in the WORLD that gets photo-chemical smog. Makes me proud to run my gas guzzler!!
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Previous:
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