Last year I finally got around to purchasing a cold air intake for my 2007 MS3. I decided to go with Mazdaspeed's own CAI(it's essentially the AEM CAI with a different filter and a splash shield) as Mazdaspeed claimed it added an additional 24 bhp. Rather than rely on the easily deceived butt dyno, I conducted before and after acceleration tests. In their June 2009 issue Grassroots Motorsports tested the AEM CAI for the MS3 using 3rd gear 30-70 acceleration times so I decided to follow suit. A nearby deserted two-lane served as the test site. My procedure was to floor the accelerator pedal at 25 mph, start the stopwatch at 30 mph, and stop it at 70. I made an equal number of runs in both directions. On both test days the ambient temperature was 88F and the relative humidity was 68%. The car had a full tank of BP 93, and the tires were inflated to the recommended pressure. After all runs were timed I threw out the highest and lowest run times in each direction and averaged the times of the remaining runs.
My results were:
30-70 mph stock filter : 5.67 seconds
30-70 mph Mazdaspeed CAI: 5.06 seconds(-0.61 seconds)
And just for giggles, I went back and checked the Grassroots Motorsports results:
30-70 mph stock filter : 5.45 seconds
30-70 mph AEM CAI : 4.85 seconds(-0.60 seconds)
Make of this what you will...
Mine: 1995 318ti Club Sport / 2014 M235i / 1999 Wrangler / 1996 Speed Triple Challenge Cup Replica Wife's: 2016 i3 REX/2009 Cooper Clubman Son's: 2009 328i