It is true that I gained 12 HP with Pro-M and K&N vs stock MAF meter & filter. I did not do separate dynos to figure out the individaul contribution but what I felt "butt dyno" if you will was that the Pro-M gave a big improvement in throttle response and a bigger kick in the pants than either my Bassani, Y-pipe, or K&N. Now, they were all on the car first so the Pro-M probably benefited from them. BTW, I think much of the benifit is the loss of the center pilar which looks like it makes turbulence NOT the fact that it is 5mm bigger. Some effect of A/F ratio probable as well though no change in fuel economy with this mod (but the K&N was worth 1-2 MPG.
Several cavats,
1) It is an SVT with #19 lb injectors (may not work well with smaller injectors).
2) Custom calibrated to my car, EEC code, filter, etc. May not work on somebody elses car.
3) I have other mods, may not benefit otherwise stock cars.
4) It has its own electronics not stock electronics like some, which I think is a bad idea.
5) I did read what Rara said about "fooling" the ECU. It does. So does the Apexi-i, MAFterburner. Some risk involved if you make the car to lean or rich. I will be dynoing again soon with wideband O2 monitoring to be sure and I have now obtained a MAF optimizer to make any adjustments in A/F (if needed). I believe this is safer than random throwing of parts on the car.
Also, I will let you know what the MAF optimizer does. I know, it offers less capability than other A/F tricker but is cheap, very easy to install & remove (plugs inline with MAF meter). I can remove my trick airbox, filter, airtube, MAF meter & optimizer in 5 minutes and replace with stock for dealer trips (I have 50K left of warranty!). One of the Cougar guys gained 10 HP with the thing. I suspect that peak gains will be near Apexi-i, but less in the middle of the curve because I can't tune at in between idle and max RPM. Custom burn chip, EEC tuner the best but require MUCH more tuning skill, carry more risk, cost much more considering the amount of dyno time and reburn costs. Anyway, these are my thoughts, will keep you posted..