the added torque seems like it might come from a bit more back pressure, is that right? maybe causing a tad more engine heat buildup? or is my logic incorrect there?

 

i had this exact setup with my stock g35 exhaust/stock CATs for for a few days (waiting for parts) and it defiantly smoothened out the VQ sound.

 

thats what i dont want, i love the vq sound, just hate the rasp

 

No, its not from back pressure. The resonator doesn't create back pressure. Its due to the resonance of the resonator.

Just a side note - Back pressure is never beneficial to this engine when NA. See this link for details on back pressure testing.
http://my350z.com/forum/intake-exhau...k-for-n-a.html

 

thanks for that link, exhaust is a pretty simple concept, but gets complicated quick when looking at the details. i havent read that entire thread yet, but it seems like exhaust velocity near the engine is what should be most desired for scavenging, which makes power. good stuff. what exactly causes the rasp sound though???

 

Shock excitation.

Basically anything that causes abrupt reflections. Sudden expansions or sudden contractions. And anything else causes a significant and sudden disturbance in the flow.

 

i see, and can those excitations come from anywhere in the system, or is it mainly from pipes close to the engine? basically im asking if those excitations could come from the muffler in the back, or stricktly from the pipes farther upstream from that?

 

The closer to the engine, the more likely it is to happen.

 

thanks, i have stock manifolds, then kinetix cats, then the stock ypipe, so im guessing its the ypipe or i just need to tighten my cat bolts

 

Maybe the cats are damaged? ie.. the brick is partially blown out and is creating that rasp

 

i looked at them before i put them on, looked good as far as i could tell. before these, i had no rasp with gutted stock cats. i didnt gut the first bricks, but i removed the second brick in each cat so that the 02s wouldnt freak out. it was all fine for a while, then i threw a catalyst inefficiency code so i think one of the first bricks was damaged. put the hfcs on and have a ton of rasp, i will try and tighted the bolts this weekend