Stock Airbox and Air Temperatures

[bullmand]

Since I got my Christmas present (http://www.scan-gauge.com), I've been using it to monitor the intake air temperature. Several years ago I modified my airbox (http://www.318ti.org/notebook/M44_dual_intake/index.html), but I've never had any real information about whether this actually accomplished anything. So, here's what I've discovered:

1. As long as the car is moving, the intake air temp stays within a few degrees of ambient (as indicated by the gauge when the car is first started).

2. The temp will rise slightly if you're idling for extended periods of time, but it drops back down fairly quickly once you're moving.

3. When the car if fully warmed up and parked, the air temp will rise 30 to 40 degrees just sitting there. Again, it drops very quickly once the car is moving.

These observations are obviously only based on temperature and I've not considered airflow or filtration, but there is plenty of info on those issues elsewhere (http://www.bobistheoilguy.com/airfilter/airtest1.htm) on the internet. My personal belief is that the M42/M44 dual intake is the best possible set-up for our cars with regards to cold air induction and adequate filtration. The only further adjustments I intend to make is to install some Dynamat (http://www.dynamat.com/products_automotive_dynamat_xtreme.html) on the side of the airbox that faces the radiator as this seems to be the source of most of the heat that the airbox is exposed to. There's very little space between the corner of the airbox and the expansion tank on the radiator. I suspect that some good insulation in that area could keep the moving air temp even closer to ambient and hopefully reduce the heat absorption while the car is parked. I'll let you know how it goes. I'm also interested to see how these readings change as the weather gets hotter and more humid. Comments and criticism are expected and welcomed.

[DustenT]

Nice work. I'm glad someone finally has some hard data to back up this theory. If I remember correctly there is some air flow data published somewhere on the web too for the fogged airbox. EDIT: Found it.

http://mz3.net/articles/images/149-m44_airflow.gif

Link to fogged airbox info: http://mz3.net/articles/149.html

[GhostRyder]

yea im fixing to fogg mine pretty soon when ever i get the time

[DailyD]

Since I got my Christmas present (http://www.scan-gauge.com), I've been using it to monitor the intake air temperature. Several years ago I modified my airbox (http://www.318ti.org/notebook/M44_dual_intake/index.html), but I've never had any real information about whether this actually accomplished anything. So, here's what I've discovered:

1. As long as the car is moving, the intake air temp stays within a few degrees of ambient (as indicated by the gauge when the car is first started).

2. The temp will rise slightly if you're idling for extended periods of time, but it drops back down fairly quickly once you're moving.

3. When the car if fully warmed up and parked, the air temp will rise 30 to 40 degrees just sitting there. Again, it drops very quickly once the car is moving.

These observations are obviously only based on temperature and I've not considered airflow or filtration, but there is plenty of info on those issues elsewhere (http://www.bobistheoilguy.com/airfilter/airtest1.htm) on the internet. My personal belief is that the M42/M44 dual intake is the best possible set-up for our cars with regards to cold air induction and adequate filtration. The only further adjustments I intend to make is to install some Dynamat (http://www.dynamat.com/products_automotive_dynamat_xtreme.html) on the side of the airbox that faces the radiator as this seems to be the source of most of the heat that the airbox is exposed to. There's very little space between the corner of the airbox and the expansion tank on the radiator. I suspect that some good insulation in that area could keep the moving air temp even closer to ambient and hopefully reduce the heat absorption while the car is parked. I'll let you know how it goes. I'm also interested to see how these readings change as the weather gets hotter and more humid. Comments and criticism are expected and welcomed.

Bullmand thanks for the research. Hard data is so valuable. I would like to do this mod as well and I have a few questions for you.

1. Do you have any other performance mods like a chip or and exhaust to take advantage of the increased air flow?

2. Have you observed any increase or decrease in performance and/or fuel efficiency?

3. What does the modification do to the sound of the vehicle? I use mine as a daily driver and would like to maintain a fairly quiet passenger compartment especially at cruising speeds.

4. Do you think the foam internals everyone recommends removing did much for air box temperature or was it just sound deadening?

I can not see how this mod would in anyway damage the car or decrease performance. Hydro locking seems as unlikely as it would with the stock set up. In addition, air flow/turbulence through the intake should also remain close to stock, just increased. It seems for the performance gains discussed and the data DustenT has posted, this set up may provide the best bang for the buck. Please keep us informed and again great job!

[bullmand]

I'll try to answer in order:

1. I have a Supersprint cat-back exhaust. No chip

2. My average MPG over the last 95 fill-ups has been 29.28. Not that I've been keeping track ;) That includes AC and wide tires during the summer and about 8 autocrosses a year. Performance is more subjective. Honestly it's been so long since I did it that I don't remember if I really felt a difference or not.

3. There may be slightly more engine noise than stock, but again I don't remember. It's definitely tolerable. I suspect after a few days you wouldn't even notice the difference anymore. At cruising speeds I would say it's not noticeable at all. The road and wind noise are certainly louder than the engine at steady speeds. If anything you'll notice it if you're really getting on it from a stop. Part #4 (http://www.realoem.com/bmw/showparts.do?model=CG73&mospid=47506&btnr=13_0417&hg=13&fg=20) is a resonator to keep the engine noise down. It probably does more than the foam could ever hope to do.

4. You'll see when you get in there, but I don't think the foam was for anything other than sound. If you were really careful you could probably retain the foam and the plastic cage that holds it in, but if you read this you'll see there are good reasons (http://www.318ti.org/forum/showthread.php?t=11291&highlight=airbox+foam) to get rid of it. What's really scary is that there is more of it in the lid of the airbox upstream of the filter. I just remove mine a couple of weeks ago. I'd clear that out while you're in there.

The only thing about this mod that is a hassle in any way is that it seems to collect more dirt in the bottom of the box. I'm assuming this is because of the direct path from the front fascia into the box. It's no biggie. I've cleaned it out once since I did it and there was just a little dirt and some small plant debris in there. It sounds worse than it was and it was all clearly stopped by the filter. I would imagine that the M42 equipped cars have this problem too since that intake path is stock for them. No biggie. Hopefully sometime soon I'll get the Dynamat on my airbox. I'll try to remember to get some pictures and put them in my gallery. I'm really interested to see how that will affect the intake temps. I'm really hoping it helps with the rise in temperature while the car is hot and not running. I'll keep you posted.

[bullmand]

So, two years later I'm going to finally update this thread with the information about the Dynamat.
I removed the entire airbox assembly from the car and put Dynamat (Extreme, I think) on all the exterior surfaces of the airbox and the intake tubes that face the radiator or the coolant hoses. That left me with the sticky tar side on the box and the shiny side facing the hot stuff. The apparent effect of this on the intake air temps was: none. The temperatures didn't get any lower than the original few degrees above ambient I was getting before. If there was any change, it was that after sitting with a hot engine it seems to take just a hair longer for the airbox to cool off again once the car is moving. I can only speculate that the Dynamat is absorbing some heat from the cooling system and then holding it in a little better than the naked airbox was. It's not noticeable enough to cause me to try and remove the stuff. I don't need that kind of hassle. One other side-effect is that the intake noise seems to be slightly less with the Dynamat in place. This makes complete sense since that's what the stuff is really for and I suspect it's just making the airbox assembly less resonant. Anyway, there it is. The materials were more expensive than the parts for the airbox mod and I don't think it was worth the cost and the effort.