Replacing the cats with either HFCs or test pipes is typically one of the biggest gains provided by a bolt-on. It won't make 'bunches' of power, but it will certainly make more than any intake or similar mod.

HFCs should produce zero rasp.

 

I love my HFC/nismo combo. It sounds pretty stock until you get into the upper rpms. Next to the a spacer, it is the best bolt on you can do.

 

The amount of rasp from the Nismo+HFC combo is so minute you won't notice it. I have the UR HFC's and Nismo and it sounds really good.

 

Hi,

I just installed helix v2 TP's with my nismo exhaust. And i must say that it is FREAKING LOUD! an obnoxious loud... I could actually live with the db increase but the drone & rasp between 3-4k is unbearable. I will be running these until I can purchase a nice set of HFC's.

However, I must say that the power increase is DEF noticeable, especially in the mid to upper rpm range. I was quite impressed.

Cheers,

 

What high-flow catalytic converters did you order?

 

sounds better than your current set up!

 

I have the Nismo exhaust, with UTR high flows, and there is a slight rasp at low RPMS that goes away when the cats warm up. If it's warm enough out, it wont do it at all, but it is there in the winter and goes away after 5 minutes of driving.

Un-resonated tp's are VERY loud, and are fun for about a hour and then it gets old. Resonated tp's sound good as well and still have some rasp, but are much quiter to the non-resonated.

I like my HFC's and it sounds great, headers adds more deepness to the sound, and it gets slightly louder, but not much.

 

how are the stillen hfc?

 

Over priced like everything else they sell.

 

does anyone know a website that has the sound clip with the hfc with nismo exhaust?? thanks

 

just got the crawford hfc with nismo and stillen intake for the 07 350z and it soundss GREATTT same goes for the performance

 

Just wanted to add about three months later they REALLY opened up and sound great.