if i have a 3 inch custom single straight pipe that BOTTLENECKS ONLY at the muffler INLET to 2.5inch will that noticeably restrict flow???? thnaks for your advice, i searched first but only found the EVO-TT BOTTLENECK THREAD which is irrelevant to my question. thanks

 

Yes.

 

NA - Who cares.

FI - Yes.

 

If you're NA why would you want 3" piping for? 2.5" is still roomy for a 3.5L v6

 

Actually it is not enough, if i remember right the factory exhaust is even bigger than 2.5

 

^ i dont think you'er remembering right.

 

Isn't there a better way? Say a 3 inch pipe into the muffler?

 

okay, my friend is doing a powerlabs ST install in September, he's currently NA but his straight pipe is UBER LOUD ( has no muffller/resonator and doesnt have his OEM exhaust anymore however he has his vibrant muffler that he used on his 95 eclipse gsx in his garage but the inlet is on 2.5 inch) and wants to reduce the noise but does not want to compromise his 400whp goal. so i wanted to ask the 350z community if that would jeopardize his goal.

i figured it would NOT since theres ppl on the forum who make ~500whp on TT setups with the APS 2.5 inch true dual exhaust. So i dont see how this would be any different IMO if the piping from the testpipe back is 3in but at the muffler inlet ONLY it bottlenecks to 2.5inches, but then again i could be wrong.

 

It depends on the tune. But from a 3" into a 2.5" then back into 3" there is going to be some bottle necking. If you're tp exits are 3" just go 3" all the way out.

 

The HR Y-Pipe collector is ~2.5in, up a size from the DE IIRC. And yes it is way undersized.

 

Exhaust sizing is less dependent on displacement than it is on total horsepower. Total power is a better indicator of total flow required.

Ex. VQ35 @ 5000rpm vs VQ35 @ 6000rpm, extrapolate horsepower made at that RPM, net output is higher at 6000rpm than it is at 5000rpm, with no change in displacement.

The energy is in the air being burned, an LS1 making 300hp burns as much air, for the most part, as a VQ making 300hp, the RPMs would be different, but the exhaust generation should be similar.

A single 3-inch seems to be the standard for the VQ, only a very few select aftermarket companies have opted for a different diameter.

To OP: It's really hard to say whether its choking, at least not without further analysis, if the transition was kept smooth it'd be better than if it simply stepped down. The exhaust cools quite a bit while traveling from the engine to the tailpipe.