It doesn't matter, any decent exhaust shop can weld the 2.25 pipes to fit into the 2.5 magnaflow.

 

Unless you use a nice transition piece, it won't be smooth. Do you have some type of data that suggests a 2.5" X and all the piping back at 2.5" would help performance and not hurt the low end?

 

its goin to sound sick!

 

I wouldn't do it. I think it will hurt exhaust velocity and kill low rpm power. I specifically remember reading in SCC magazine a few years back about a VR6 VW drag car that had a single 3" exhaust and the tuner took it down to 2.5" and saw a gain of about 15whp because of the improved exhaust velocity. The VR6 was stoked to 3.2 liters and was making about 325whp NA.

 

You know, maybe for the older VQ this was true. But now that HR loves the 3 inch exhausts. Many 350z's with the HR are getting like 15 hp from an exhaust that was made for a FI car. Before and after dynos. Different brands of exhaust.

I didn't believe it at first, but people keep posting dynos lately of them, and after seeing a few, I am really surprised! Whatever Nissan did to the HR it likes Exhaust systems especially 3" over 2.5".

 

Interesting. Even with a full 3" catback? I know that the exhaust gains have been decent with the HR motors, I just hadn't looked into it that deeply yet. I'm still not convinced the intakes for the HRs are very effective though. I think daily about getting an HR 350Z

 

I agree with the intakes. That is the reason I am still stock.

If K&N would release filters for the HR though, that would be nice.

 

http://www.my350z.com/forum/showthre...light=TURBO+XS

 

Russ if I had the choice, look to see if Amsoil or AEM has replacement oem filters for you. The Eu Amsoil looks to be a great filter. I've been meaning to try to match a cone for my Stillen.

BTW. I've been tracking my mpg with the navi. When I first did the exhaust the mileage went to *****. But after 3/4 tank, it's indicating 19.5 mpg or so. That's actually a tad better than before the exhaust. It certianly not worse. I'll chime in again with the mpg after the tank is done.

 

2.25 is more than enough for up to ~425whp on the sedan. That's what I'm making with my Borla.

 

My Borla just got installed, ans I couldn't be happier.
Sounds really good.

 

A guy on the Z forum put in the Magnaflow resonated X on his Z borla. Said it quieted down the rasp of his test pipes. It's hard to tell exactly where he put it but since he kept is resonators, he had to put it right after the Y.

 

Whats louder, the Stillen 2nd Gen Catback or the Borla Catback?

 

I don't have either, but the general consensus on the forum is the Stillen Gen2 is far louder than Borla.

 

I love my Borla.