Here is a dyno comparison of my 05 auto TSX with header and ghetto icebox VS header, RT cat, UR pulleys, 25 degrees hotter and fully stock air filter assembly. Testing was done on Dynojet machine, here in Sacramento.
First run- 174.08 WHP
Second run-167.08 WHP
As you can see, the car lost 7 WHP with the intake assembly returned to stock and temperature increase of roughly 25 degrees (55-80). Also, I changed stock Michelins for much softer Nexen N5000 tires so that could add a bit of rolling resistance while the car was on the dyno "bump". This is serious considering the fact that I had RT cat and UR pulleys installed AFTER the 1st dyno.... I used exactly the same type/brand of oil and fuel in both runs (Mobil 1 synthetic/Cheveron 91)
CONCLUSION: The intake is assembly and temperature of air are VERY important
Since then, I once again removed the intake resonator and did TB bypass. The juicy gain can easily be felt, especially in cool nights when it take some time for heat to be transferred to the intake manifold.
I will test the car with my current set-up before and after getting a single-outlet cat-back later this year
