[emjei]

I notice that catbacks keeps the middle pipes in place...

What is the advantage of them...just eliminating the last back pipes ???

Sound??? What about HP ???

[SV Concepts III]

It really depends on the brand but typically a Cat Back Exhaust will replace the center pipes as well (everything from the headers to the rear mufflers). Since the OEM is a single unit, it doesn't make sense to cut it up and keep the center restrictive piping.

Here is a shot of the Active Autowerke 335 Cat Back Exhaust installed on our 335. This replaces everything from the headers back to the muffler and gives the car a nice growl that is not too loud or overbearing.

[xsb00st]

Originally Posted by emjei

I notice that catbacks keeps the middle pipes in place...

What is the advantage of them...just eliminating the last back pipes ???

Sound??? What about HP ???

Catback is deceptive with the 335i. It really should be called "downpipeback". Most full exhausts systems (AFE, Britalmen(sp?), etc.) provide an entire system that bolts onto the downpipes of the 335i. These systems replace the secondary cats, or the middle pipes you describe. These middle pipes are usually considered Section 2 of the exhaust system; so the catback exhausts you're mentioning are really bolt-on section 3 systems and really have no, or very minimal HP increase. To see any performance increase you need to install a system that removes the secondary cats and improves exhaust flow.