So i changed the cats and put on the torqen Helmholtz test pipes on an otherwise stock car and since I’ve done that there’s been a pretty consistent hiss coming from the rear of my car and i can hear and feel a tapping a certain times when i press the gas peddle (around1-2.5k) and it’s significantly louder in the cabin than it is from the back but im also not smelling the exhaust from inside the cabin ive chocked it up to i probably need new hardware and possibly a new CBE because the test pipes are 2.5in through and thought I’m not sure if there’s a significant difference between the y pipe inlet and the tp outlet if i could get anyone else’s input on the matter I’d be appreciative

 

VQ hiss. You've found out how these engines sound.

 

Y-Pipe inlets are closer to 2", but as victory noted, the "rasp" seems to accompany aftermarket test pips and high flow cats. Typically, some form of downstream resonators are needed to eliminate.

 

My dudes, I've got resonated HFCs and double-resonated catback and it still hisses like a ticked off snake when getting off the gas. No problems with the car or with tune or with power, and no leaks.

I'm guessing it has to do with the fact that the throttle bodies are basically full open when the car is running and the valve timing and lift adjustments are what throttles the engine.

 

I don't think the hiss comes from the intake side as it's typically louder the more open the exhaust is. The intake has its own set of noises because of VVEL, for sure. I hear the hiss a little with my Kinetix HFCs and Invidia Q300, but that setup is about as quiet as aftermarket exhaust gets on these cars. Maybe an unpopular opinion, but VQs sound kinda terrible when they're loud