[gT-BMW]

Hey guys i already have AA headers so its primary cat delete and im thinking about deleting the secondary cats and add an exhaust cut out between the muffler and resonator. anybody running one of these? if so does it actually add power or decrease it? Does it sound like stock with it closed?

[atmosphericM]

Do a search this was just discussed here a couple of months back.

[The Nightman]

Seems pointless when you've already deleted all the cats. The rest of the exhaust isn't restrictive enough to warrant a cutout imo

[Taskmaster]

Originally Posted by freedomfries

Seems pointless when you've already deleted all the cats. The rest of the exhaust isn't restrictive enough to warrant a cutout imo

It is, but it will sound like shit, and could make less power depending* on where the cutout is.

[nsjames]

and 95% of the time they leak. so you'll always hear a terrible exhaust leak.

unless you buy realy quality units that are cost prohibitive.

[gT-BMW]

Originally Posted by atmosphericM

Do a search this was just discussed here a couple of months back.

yes i was reading those threads, there were more towards the sound rather than performance. nobody was clear if it actually added hp.

Originally Posted by freedomfries

Seems pointless when you've already deleted all the cats. The rest of the exhaust isn't restrictive enough to warrant a cutout imo

so the stock muffler is not a restriction? if so thats sweet.

Originally Posted by Taskmaster

It is, but it will sound like shit, and could make less power depending* on where the cutout is.

I was always told the cutout mod on a bmw should be done towards the rear of the car or the afrs will be to crazy?

Originally Posted by nsjames

and 95% of the time they leak. so you'll always hear a terrible exhaust leak.

unless you buy realy quality units that are cost prohibitive.

I have a 2.5 dmh cutout from a previous n/a honda build that i did many years ago. still have it. and that one doesnt leak. Ive tried other cutouts, they did leak, they eventually leak because the housing butterfly slightly warps after awhile and the motors would break off or stop working. QTP was the worst. IMO dmh is the best cutout on the market.

[atmosphericM]

Ok well here are my two cents:

1. It will sound like crap. Mufflers refine the tone. But if this is purely for when you are racing, then ok. To each his own I suppose, but there is a point when you are seriously infringing upon the comfort of those around you. When a modded Harley drives by and I literally have to plug my ears for them to not hurt, I roll my eyes so hard. I mean wtf, really. Some places even have laws against this, with good reason.

2. Yes it will probably give you about 5 whp to bypass the muffler. But you'll also hurt your hp a bit when it's closed because of the turbulence it will cause in the exhaust stream. Also, a tune is becoming more and more necessary to fully utilize your exhaust mods with each one you do. Personally I wouldn't even run headers without an aftermarket tune as they're already probably affecting the AFR's (not sure how much our DME's can "adjust" to engine air mods). With catless headers, catless front pipes, and an open cutout, the air flow is so much freer and different than stock, a tune is really needed to enjoy the benefits. Without a tune, some top-end HP gains may be happening, but almost certainly at the expense of low-end TQ.

3. I could be wrong but I'm thinking that there is only one place you can even put the cut-out, which will require a different mid-pipe (y-pipe), because in stock form, the resonator is in this location. The rest of the exhaust "area" under the car is pretty tight... but perhaps you could find another location... maybe.

4. Would it sound like stock with it closed? No. You already have headers, your car already doesn't sound like stock. If you delete the secondary cats, your car is going to get louder and raspier. It wont be super loud or raspy, thanks to your stock muffler, but it will be noticeably different than stock when the motor is under load. With a cut-out it will be deafening and, to anyone above the age of 25, annoying AF.

5. There is at least one good YouTube video of a guy with a cutout on his 328i. That should give you an idea of sound.