Modding the Stock Airbox????

[justin11572]

I do know the best way to go is to install a CF airbox for great sound and power. Right now I already got rid of the AFM by means of a piggyback system...MAP ECU. For the moment I don't have the $$$$ to get a CF airbox so I am asking you guys if there is any way to mod the stock airbox system to at least improve the sound and perhaps the power if possible? Removing the box is out of the question since I really don't like the idea of running velocity stacks alone, it sucks hot air, and filters are hard to find here.

Hope you guys can throw in suggestions....

[UweM3]

I have a second plenum lying in my garage for a modification. Basically I wanted to move the air intake like the carbo airbox to the front and close the side.
But then I got a a carbon airbox on loan and went to the Dyno. I bought one four weeks later.....

[Ironhead]

Here is what I did a long time ago.

My main goal was to remove the AFM, and hopefully to have the filter assembly breath as well as possible. I can't prove their was any improvement beyond the removal of the AFM, but the car made very good power with this setup.

I used this until I switched to a CF airbox.

If you are talking about modifying the aluminum plenum portion that bolts to the TBs, I can't think of anything useful you could do to that.

[justin11572]

Thanks guys...

Yes what I wanted to mod is the part that bolts to the throttle bodies, and not the airfilter assembly. From what i recall the stock ones have velocity stacks bent 90 degs, which I thought of removing/cutting, though I have no plans of moving the inlet to front instead of the from side. Anyone try this???

[F0Bman]

The internal horn is great because it increases the flow of the air in the whole setup.

[justin11572]

oh ok, so i guess shortening the internal trumpet looking runners will do more harm than good? I planned on shortening them a few cm to get better sound thinking power loss in the low end would be negligable....

[m3pat2]

Hi justin...yes you'll loose mid range power, but the sound will improve. You can really hear the intake because the horns point directly at the opening of the plenum and the sound waves pulse right through my MAF conversion.

With the stock runners the intake pulses are muffled since they point away from the intake 90 deg. elbow and they are much closer to the plenum wall near the elbow.

Here is my setup and my velocity stacks end right where the blue line is:


I would not recommend shorter velocity stacks on a street spec'd M3.