I had Headers and test pipes as a combo with the stock cat back and there was a noticeable gain in higher rpms and speeds .

the sound was good above 4k but at 2500-3000 there was nasty, nasty rasp with the test pipes (not with headers + stock cats though)

I switched to Resonated test pipes with the same headers and stock cat back and did not notice a drop in power, but the rasp was minimized and only occured from about 3k-3200 which was better as cruising rpms are in the 2s so the nasty low speed rasp was gone.

sounds mean at WOT though.

 

I have test pipes and a Tanabe Y-pipe with the rest stock. There's rasp from 3-3.5k. It basically just makes the stock note louder. I did a before and after on a dyno with TPs and a plenum spacer. The TPs and plenum added ruffly 10 more hp to the wheels.

 

A reflash would have probably ailed better HP figures, imo.

Motormouth: Good, because I plan to get res. pipes, anyways.

 

right now I have aps test pipes on a otherwise completely stock exhaust system, and no drone what so ever. I do however have a nasty bit of rasp but only at pretty much WOT.

I did notice a deffinate horse power and torque increase. however alas my stock exhaust is still far to quiet so it's time to spice things up a little bit. hense the Injen track on it's way . I'll let you know how it goes

 

I just installed HFC's and I retained my stock headers, ypipe and muffler section. The car sounds a little deeper at idle, but not louder. it has more of a European, rich sound (basically this mod accentuated the beautiful sound of our motor.)

I do hear a slint hint of rasp @ WOT. But nothing too bad. I need to ensure I don't have any exhaust leaks, but I'm terribly pleased. the accel does feel slightly better. I don't know how much "faster" it is. But It feels like it revs faster. doesn't seem to have hurt the bottom end.

oh and absolutely no Drone out of these cats.