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Re: M30 AFM differences, applications, etc (archive)
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Posted by Lui on April 30, 2001 at 03:57:10:

In Reply to: M30 AFM differences, applications, etc posted by Steve on April 29, 2001 at 16:04:19:


What are the differences between the different AFM's, how are they distinguished, and what do they do differently? I have a custom built 2.8liter M20 engine that could use some more airflow and know I want to implement an M30 AFM I just don't know which unit I need.

Steve
'86 325
'87 328iS
'88 M5 (in the works)


Hi Steve.
You can get information about the differents kinds of AFM if you contact Bosch.
The differences are basically the resistance range of the col potentiometer which send a resistance value to the ECU or EFI unit. Actually there are not large differences betwen AFM in the stocks M 20 2,5l and M30 2,8l.
The AFM 2,8 lt is a unit bosch ref nr. 0280 202 025, the resistance range in the flap is about 60 to 1000 ohms when this is close and open.
A AFM bigger is the unit 0280 203 027 which sits in the stock 3,5 lt. the flap range is betwen 100 and 2500 ohms. You can see that this resistance range is to big if you compare with the 2.8 l stock.
I think you can increase the air flow if you use a direct air flow filter. You can also install a fan betwen the AFM and the air filter.
The combustion process is more efficience if the combustion air is cold and if this get to the engine as soon as posible.
The air density has a inverse relation with the air temperature, to low air temperatures the air density is higher, this is much better for combustion process than a low air dencities.
In other words the power can be increased if the combustion air is cold and if this reaches the engine fast.

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