So, from what I understand, the stock exhaust has a 2" diameter until the Y-pipe, and 2.5" when it leaves the Y-pipe, all the way until it exits the muffler. All the high flow cats I see on the market have a larger diameter, with most being 2.25". If you keep the stock exhaust and switch to some HFC's, that would not be optimal air flow pressure, correct? It would be going from 2.25", to 2", to 2.5".

So in other words, if you get some high flow cats, shouldn't you switch everything out after that to a larger diameter as well?

 

imo yes

 

What he said ^

 

Kind of. Volume and velocity is restricted to the smallest component. If you add 2.5 inch test pipes, then go to a 2.0 inch exhaust you have achieved little. Except...

Test pipe is just an empty pipe so it is more efficient than the OEM catalytic converter.

 

You should yes, but its still a gain on stock exhaust. At least from my experience with test pipes.

Your keyword was optimal though. Sounds like you have the right idea.

 

search fro "hydrazine" tony has done hours of testing diameters to get his exhausts right and will conclude that 2" was best for test pipes, 2.5" into Y and 3" out, anything past that is too far from the engine to make a difference. however if you look at most aftermarket headers they have a 2.25" outlet

 

Are there even any test pipes or hfc's out there which have a 2" diameter?

 

test pipes yes... invidia for example are 2"

 

Sadly those are not resonated. Any others that anyone knows of? Geez I wish it was easier to find this stuff out. Most places that sell test pipes/hfc's don't even list the diameter.

 

why do u want stock exhaust? U do understand ANY modification is going to change the exhaust note of ur stock exhaust

 

Yeah I know. I'm looking for the stock exhaust sound, just louder.

Also, 2" test pipes/cats give the best performance if not FI.

 

If u add tps to stock exhaust u will get rasp. U can try the Motordyne ART pipes which are suppose to eliminate rasp and pay i think 700$ for them. Then u get a better tone then stock without rasp. If it was me and i JUST HAD TO HAVE stock sound but a lil beefier, Nismo Exhaust change out y pipe for a cheaper better 1 and get HFCs