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This is what is inside your big black "M Power" intake plenum, for those that have never had it
apart. These are the intake runners, sometimes called trumpets (for obvious reasons).
These trumpets smooth the flow of air into the throttle bodies and from there into the intake
ports. The length of the trumpets is an important criteria in determining the torque and
horsepower characteristics of your engine. The intake system is similar to the exhaust side in
that there are pressure waves which travel back and forth along its length. The pressure waves coming
out of the intake tract will reverse direction at the trumpet entrance. Thus by altering the length
of the trumpets it is possible to change the timing of the returning pressure pulse to the intake valve.
The complete scenario is quite complicated but suffice it to say that the geometry of the trumpets
will affect how your engine makes power.
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The reason that I purchased the Evo III intake trumpets is that they have a larger diameter than the stock
2.3 liter units. Since I was enlarging my throttle bodies it was only natural to match them to larger
trumpets (and larger intake ports as well). This helps preserve the "balance" of the system. The finish of
the trumpets from the factory is very rough on the newer production units. They require a lot of patient
work with porting tools to get them smooth and to match with the throttle bodies. I purchased the trumpets
from Nick Alexander BMW in LA since it was convenient. But they are available from sources other than
the dealer. Mitch Herman carries them for example.
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Evo III Intake Venturi
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p/n 11 61 1 315 264
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$314 @ Nick Alexander BMW
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