Can someone tell me exactly what part of the exhaust system is replaced when I install the Helix SS Test Pipes?
Can I expect HP increase as well as more noise with this install?
Can I do this mod before I install a Cat back system?

So far I have done
6 wire grounding kit
Nismo CAI
Crawford Plenum (disappointing)
Switch to Mobil 1
Changed Fog Lights

 

It replace the catz. You can expect around 4-7 hp gains. The sound should be slighty louder.
You can do this before installing the cat back system

<font color=green>04 G35C 6MT/Navi/Z-T/JWT/Tein S/RH C4 19x9/19x10.5/CC</font color=green>

 

Is this road legal?

G35 coupe 6spd
Twilight Blue/Tan
Fully Optioned
Nismo CAI

 

Road Legal??

Not even close!

only thing they are - cheap & high flow.

 

I think they are slightly louder than "slightly loud".

Can anyone comment as to how straight pipes sound relative to high flow cats (and even compared to stock cats)?

Is there a Rasp? Are the straight pipes Very Loud? I think this what the initial poster really wants to know to help the decision process along.

301-bhp!!! ...and growing!

 

Do a search. From what I've read, there is little to no performance advantange to running test pipes vs. hi-flow cats. In fact, test pipes are known to be quite "raspy", are known to cause CEL, and are definitely known to be ILLEGAL. If you get caught, you will not be happy. Pay the extra $150 for good cats and save yourself the headaches.