would there be a nice gain on a stock R? would the low end suffer? I am
talking the jdm 2.5 header with full 2.5 cat back exhaust. asuming the
cat is 2.5 as well. thanks for any info.

 

Gains are good.

You will be hard pressed to find a 2.5" exhaust that is premade. You will have to settle for 60-65mm systems or custom build one.

 

I got a 2.5 setup and a test pipe that replaces my cat but mine is supercharged and it sounds very nice,I would recommend it but you'll have to find someone who can do some good exhaust work

 

i actually think the low end gains are awsome on my set up. JUN JDM header, 2.5" mandrel bent from collector-->JUN MM muffler. feels really nice. usually when the lower rpms cause me to down shift to pic up decent speed, now i just let it climb, very noticeable gains

 

I think i felt a lost in low end with the new 2.5" custom catback and 2.5" test pipe. This is compared to my old 2.25" 5zigen catback and cat. both are from a jdm 4-1 header. Top end sounds much nicer with the new exhaust