Cold Airflow Modification

Here's the documentation of a modification I made to my to my air intake system. Just read along, and check out the pictures. If you have any questions about anything, just email me. See the link to my email address at the bottom of the page. Thanks and Happy Bimmering! -Chris


Hello, okay, here's what I did this past weekend (03/31/01) to improve my cold airflow. I took detailed pics of the process, to show everyone. This is a long post. The pics are big, but of relatively small filesize (9 pics, each at about 40k).

Ok, on to the disclaimer:
***NOTE*** I did this mod on my car, an '89 325i US SPEC. It's all YMMV, FWIW, HTH, FYI. Don't blame me for messing anything up on your car if you do this mod to it. I have no idea if this is the same setup, or how/if it works on euro models, the 325e, the early 318i's, or the M42 motor. The compartments and radiator and such maybe be different.

OK, procedure, and explanations, w/pics:
First, remove the front left grill. This is done by popping the hood, then taking off 3 clips at the top, and 2 screws at the bottom. Takes 1 minute to do. Easy as pie. You will then be able to see a plastic trim piece which blocks airflow to behind the headlights. This piece is vertical, and it is between the radiator compartment and the headlight compartment.

(no comments on the dirtiness behind this trim piece...)



This next picture shows a better view, and I circled the trim piece in question, for illustration purposes.



Here is a slightly different angle. Notice the tabs at the top. These tabs hold the trim piece in place at the top. What we're doing, is taking the tab off the metal frame, then we are able to bend the plastic trim piece back (to the left), towards the fan. This will hopefully allow more air, cooler air, faster flowing air, into the compartment behind the left headlights.



The compartment behind the headlights is where the stock airbox gets it's air supply from. The airbox connects to this compartment via a rubber duct. If you remove trim pieces behind your left headlights, from inside your engine bay, you'll be able to see better how the airflow is directed into this compartment from my airflow mod.

In this next pic, my finger is holding the plastic trim piece to the left. We're going to use a rod to prop this trim piece in place. Let me say right now, the only dangers I see is if the rod slips out of place, and bangs into the radiator, or the fan. Also, it is possible that long term effects of the bent plastic will make it brittle and break. Also, it does NOT seem that the trim piece will get hit by the fanblades. It has been a few months since I did this mod, and everything is holding up fine!!!



I highlighted the little tabs you need to bend back to free the trim piece from it's normal location. Just go easy on it, hopefully nothing breaks. It seems to be very pliable and bendy plastic trim.



Here is the rod I'm using to prop the trim piece. It's actually a set of disposeable wooden chopsticks, and I duct taped them together. It's also not full length chopsticks, I cut them first to fit. And chopsticks were the only thing I had handy!!! No comments on how they're good for eating rice. Hmm, maybe that's a good thing. Rice-eater. Heh.



Here are the chopsticks in place, propping open the trim piece. I stuck them in real good, so the fit was snug. This was possible because I made them a bit long, so the fit was snug, I wedged them in there. That funny tab in the body, where the left end of the rod sits, is where the left grill piece is screwed in place.

You can see how the angle created by the plastic trim I 'relocated' is condusive to allowing more air into the compartment behind the headlights.



Here's another angle of the plastic trim piece being propped to the side by the rod.



Here's the final pic with the grill trim back on. The mod is not noticeable unless you look into the front grill, at the radiator. The arrows show the way air flows past the grill slats, to the relocated plastic trim piece, then is diverted into the compartment behind the headlights. Then it go up the tube into the airbox.

The other downside of this mod I see is that less air gets to your radiator for cooling of the engine. It's a relatively small area, but sometimes all the surface area you can get helps. So I don't know. Also, don't know the effect (if any) during rainy days.



The car feels slightly more responsive, but I don't know if that's an actual VERY SLIGHT gain or just the placebo of 'I did a mod, the car is faster now!'. Hopefully it allows cooler, better breathing.

I've since installed a K&N Cone Airfilter, removed the stock airbox, and took out the 'little' baffle piece of black trim which is behind the left headlights. Also will be planning a heatshield for that, will let everyone know when I install it and get pics. FYI, I got the K&N cone airfilter adapter from an early model ('84 or '85) 318i. It fits up the the AFM perfectly. My total cost for these mods was approx. $80.

Hope everyone understood my procedure, and sees why I did it, and hopefully tries it. No harm in trying. Nothing you can't put back to stock. Happy Bimmering. Any questions, just ask away.

-Chris Chow, DBMWN2ZS


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