2.5 vs 3in. Catback

[Michael Perez]

I know exhausts have been cover numerous times but my question is: given a 3in catless downpipe as a control what would be the differences in a 2.25, 2.5, and 3in catback? Is most of the HP and TQ coming from DP?

 

[webby]

On the si, most would say you'd see the largest gains out of the 3" exhaust with mods. If you go forced induction, the same. Removing the 2 catalytic converters in the stock downpipe with an aftermarket downpipe gives quite an upgrade on it's own though.

 

[RobSBP]

2.5" exhaust pipe diameter is good for around 230hp and 3" should be about 330hp.

 

[twister8008]

Gents, I am really close to buying a down pipe. What was the average performance gain with the addition of the down pipe. I want to sound close to stock, but a tad deeper so I was thinking about RV6 or FR. I plan to use my stock cat back exhaust at least until next summer. Is the downpipe alone worth it, or should I just give up in my quiet exhaust? Which catted dp is best?

 

[Dennis Rockholt]

Isn't the RV6 downpipe only 2.5"? Will that pair with a 3" exhaust, or should I just go with the full-race downpipe to pair with my N1?

 

[twister8008]

I was told the 3 inch fr would pair with the stock system, so it should work either way. I would go with fr down pipe if you plan on getting a 3in exhaust

 

[Dennis Rockholt]

Yeah I already have the invidia N1 haha so I will probably be going with the fr

 

[Michael Perez]

UR dp with a high flow cat would tone noise down a bit. And the reason why I say UR is I believe it has the O2 spacer welded on the bung and users aren't reporting a CEL but do with the FR dp. I remember reading it on here that's the reason for seeing many people using the UR dp with the FR catback.

 

[Michael Perez]

It's good to know that you could almost never throw a CEL even if the cat goes bad. Even thought these high flows tend to still throw the CEL without a spacer.. They don't filter as efficiently as the stock ones.

 

[squiggy]

The O2 spacer isn't relevant if you are having it tuned with FlashPro though. If you are getting a DP, you should really be getting the car tuned anyway.

 

[Michael Perez]

This is true^