I have Nismo catback and popcharger on my car. And I had just installed a set of Helix testpipe last night. It is Raspy... which I loved the sound when my Nismo catback with the cats... But i do want the extra few hp.
As i remember, there was a post about adding aftermarket upper plenum would get away some of this raspy sound, is it true?? since i was trying to search that thread, and I couldn't find it.

 

The plenum will not effect the rasp. I would suggest that you go with a resonated testpipe, as this will help muffle the raspy sound.

 

then what are some brand that make res test pipe?

 

Labree Motor Sports

 

or you could gut your stock cats. yeah I know its the cheap way to go but there wont be any rasp and you will still get about the same amount of ponies as just a testpipe. I plan on doing this mod next week since I hated my testpipes as well.

 

If you plan on going turbo it does eliminate the rasp with those TPipes. I would recommend high flow if your NA.

Later

 

i want to keep the factory cats, in case i have any problem with my engine, so i can put it back to stock, and go back for warranty...

so only Labree??

I am planning on staying NA...

 

is it ok to just weld 2 resonators onto the test pipe??

 

theres also kinetix and megan racing.

i have the labrees and i'm very happy with them.