K&N Typhoon results
I just recently installed the K&N typhoon intake for a 2005 WRX STi (K&N #69-8001TWR). Fairly nice kit, once everything is pieced together. Basically a short ram cold air intake box setup. It does look really good in the engine compartment, since the wrinkle powder coat matches the STi intake manifold. Airfilter itself is fairly small though, about 4.5" high and 4.5" wide at the base, not really big enough for a car starting out at 300 h.p.
Anyway, my car should have picked up about 13 h.p. or so above 4500 rpm according to K&N's dyno results. Uh,uh. I guess what works on a DSM does NOT work on a WRX. I could tell idling the car was lean, exhaust note got really loud and boomy. I knew right away something was NOT right about the car.
Took it for a spin expecting it to rev faster, nope. Car could barely get out of its own way, throttle response was dog slow. Boost response however was quicker, but with no power. Felt like major ignition timing retard. I would say I lost about 40-50 ft*lbs across the board. I lost that hit of torque right around 3700 rpm that plants you in the seat.
Anyhow, I uninstalled it, went back to stock, and all the power came right back. The K&N MAF pipe was so hot I could physically not touch it. I'm sure this heat soaked right into the MAF sensor. How the MAF is getting thrown off I'm not sure, the K&N intake pipe meausures 2.600" internally. I think I'll buy an Engine Management system, then put the K&N back on, but right now its faster without it.