996 MAF Housing Diameter
 

i am looking to verify the INNER diameter of the stock 996 MAF housing (1999). The number I have is 84mm. Can anyone verify this is correct? Thanks.

I don't remember the exacts, but if you are looking to get one. You can buy a cayman S houseing. The only pain about that is that it comes with the sensor so there damn expensive, The alternative is to get a BMW mass air houseing, same part. I don't remember what model or years but they come with out the sensor and are cheap and correct. I believe that a 2000 540i is one of the models that the housing is a direct fit for us. Just some stuff to think about.

J

Spell check not working so well?

JAAY -

good call; the E39 540i housing is a match. i picked one up from a guy on bimmerforums.com for $40. thanks for the advice!

what was the inner diameter of the 996 and 540i Maf housing? Can you tell me the OD also?

Would there be any advantage to using a 996/540i larger housing with the regular 986 maf sensor if connected to a cone filter on one end, and, for my current setup to a larger 3" through hose/pipe with 75mm TB and IPD plenum?

Absolutely not. The OP needs a 996 sized MAF because he will be running a 996 map on his 3.4. A 996 sized MAF on a 986 map would give horribly inaccurate air mass readings, and the car would run poorly.

If you didn't know, the actual MAF sensor is the same, it's only the housing that is a different diameter.

While I realize you may have a larger TB and aftermarket plenum, the DME still needs accurate measurements of air mass, and that depends largely on the size of the MAF housing matching what the DME was calibrated to expect. The DME's used in the cars are very good at adaptive learning, so if there were to be any gains to be had from your setup, after a few miles your car will have learned to compensate for the added flow (if any).

cloudsurfer is right; your air fuel ratio will be miscalculated if you run the incorrect MAF housing diameter.

if you are just looking for a flanged MAF housing with which to make a cold air setup, the MAF from the E39 BMW 535i (the V6) has the same inner diameter as the boxsters.

One piece of advice you should take. Get a wide band O2 put in when you are done. I thought my car was running great. Turns out I was running a bit rich. I have since dialed it in and the car gets great mpg and makes a ton of power.

Keep in mind that the positioning of the MAF sensor in the intake track relative to the throttle body and the air filter is as important for MAF voltage to air mass calibration as the the diameter of the housing the sensor is placed in. The 5.2.2 DME cars are extremely sensitive to this.

-Todd

what changes with position, i wonder? IAT?

Flow speed is irregular through a tube, fastest at the center fully developed, 0 at the walls. If the sensor is near a bend, diameter change or near a filter, it will be irregular (not the nice, parabolic velocity profile) and need to be tuned.

ah. we used to use some rules of thumb in development of fire suppression systems. if it was single phase flow, i.e. CO2, we'd use 1X the pipe diameter following an elbow or tee prior to pacement of another elbow or tee.

with dual phase compressible flow (i.e. FM-200 w/ Nitrogen), we had to be more careful; the tees & elbows would cause collapse to the liquid phase & we'd have to give it 2X to 3X the tube diameter prior to tees, otherwise all the gas would go one way & all the liquid would go another.

with the intake stuff here, we're using much lower velocities & i would think it would matter a lot less. what do you think is reasonable? 1X the tube diameter?

The problem is, it has to match the 996. If they dialed it in near a bend or filter, you have to do the same thing. And be in the same relative location to the bend with regards to the circumference of the tube. So it's not a matter of you picking a good spot to start from, it's you having to pick the same spot that the ECU expects.

blue, you are a smart man. that makes perfect sense. looks like they come directly out of the airbox plenum & into the MAF. after the MAF, it's straight to the throttle.

http://i156.photobucket.com/albums/t.../996Airbox.jpg

Excellent advice. Unfortunately, there's only so close you can get practically. The fact that these MAFs do have the smoothing grids certainly helps, but I don't doubt that my car would benefit from a custom tune.

You could do a calibration on a flow bench and be sure it's right, but there's alot of effort involved there and then if you can't get the position quite right, you would still need to tweak the ECU or sensor.

The final tune is the best way to make sure everything is working as expected.

if that's the case, might as well just design the intake that fits / flows best & sort out the MAF readings later.

Is this still valid information for a 3.2L 2000 S? What is the exact id of the stock MAF housing?