Cold air vs open filter data


Founding Member
Jun 6, 2000
Phoenix, AZ
I'm in the process of swapping over to an 80mm Pro-M and custom 4" intake tubing. I wanted to figure out if there was actual anything to gain from shoving the filter through the fender to get to "cold air."

It occured to me that since I can data log ACT with my Tweecer I can answer the question. So, I used my old setup (conical K&N sitting right where the stock air box sits) and then switched to an old Moroso cold air kit I had sitting in the garage.

I used the following routine both times:

I drove around and warmed the motor up to normal operating temp (about 180 ect). I then drove aorund for 10-15 minutes at speeds from 0 to 40 mph and monitored my ACT.

Outdoor temp was about 100 degrees. ACT was exactly the same in both cases. It ranged from 165-175 throughout both drives. It was even the same while stopped at idle for a couple of minutes.

For other cars, the data *may* vary. I have a very open engine bay - no smog, no a/c or p/s, and a cowl hood. A stock restrictive engine bay *might* give different results.

For my car, there is no advantage to putting the filter in the fender.
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Useful data - thanks for posting it, and for posting it the way you did - with all the facts about the test. Were you able to measure ambient temps adjacent to the filter in both locations? That would give us a clue as to whether the air stream simply picks up heat soak from the intake equalizing things, or if you had air around your filter that was the same temp as the air in the fenderwell.
No, I need to use a thermometer and measure the ambient temp difference at some point.

I imagine my results are a combination of having a well ventilated engine bay to reduce the ambient temp differences and the manifold heat soak equalizing the air temps by the time the air reaches the act.
I would interested to see if insulating the CAI and subsequent air intake pipes would do anything to keep act's down. If you do enough combo's, I would acutally comtemplate paying a nominal fee for the information...especially if you got into MAF sizes, throttle body sizes, heads, cams etc.

Thanks for that info. :nice: