[Herakles]

I really am tempted to install a cat less down pipe on my n55 e90, but can't tell from the videos how loud and obnoxious does it make the interior noise?

I'm getting my fmic and going mhd s2 and would love to be FBO... but worried about that noise- is still be running stock catback

[TheGoodTheBadTheUgly]

Originally Posted by Herakles

I really am tempted to install a cat less down pipe on my n55 e90, but can't tell from the videos how loud and obnoxious does it make the interior noise?

I'm getting my fmic and going mhd s2 and would love to be FBO... but worried about that noise- is still be running stock catback

If you plan on driving in high RPM then you are going to notice that the noise is louder in the cabin. But seriously if you cruise normally on the highway in high gears or around town at lower RPM in any gears it not really a noticeable difference or like near an annoying level at all.

[El_J7]

Its not that big of a difference as for loudness imo. You will notice the smell tho.

[Cloverdale]

No smell what so ever on my n54 and not noticeably louder.

[uber]

Originally Posted by Cloverdale

No smell what so ever on my n54 and not noticeably louder.

No smell because n54s have secondary cats. Only the x-drive n55s have secondaries.

[Herakles]

Originally Posted by uber

No smell because n54s have secondary cats. Only the x-drive n55s have secondaries.

So would i smell anything being I have n55?

[uber]

Originally Posted by Herakles

So would i smell anything being I have n55?

Depends how sensitive your nose is. I'm sure it's dramatically different with the secondaries. My friend with an N54 said he doesn't notice the smell at all.

[BazIRL]

Not much of a increase in noise at all untill you get on it with valves open, smell is noticeable depending on which way the wind blows, cold start is way louder.

[TheGoodTheBadTheUgly]

Concerning the smell on xDrive, you can sense a difference for sure but not to the point where it becomes annoying or discusting. You will defenetly have a smell of raw fuel that is more pronounced if you stand at the back of the car, but let's say you are stopping at a red light with your windows oppened, you would be able to pick up a more pronounced smell but not much more than that.

Keep in mind I am running a performance exhaust mod setup so it's most likely even better on stock exhaust.

[Herakles]

Guys, in some older threads noted the x drive has secondary cars too, and sounded like the smell is barely there if at all- but the non xdrive don’t have secondary cats and they really smell.

I would think a down pipe upgrade on the xi models give more hp return since they have primary and secondary cats so pretty restrictive vs the non xdrive that have only the primary downpipe cat

[Vivek.]

I have catless DP's with secondary cats in place. Smell is definitely noticeable IMO but not really a nuisance. Similar to my GSXR 750, I'd say, which never had cats.

I have a friend who's fully catless on his N54 and the smell summarily is horrendous--can't have any of the windows or sunroof open or even cracked at lower speeds. I will say though: that car smokes noticeably, especially on startup--so this level of smell may not be normal behavior on a fully catless N54/55

[anjuna]

catless DP was imperceptible to me in-cabin. BMW has sound deadening down to a science.

YOU will notice it, but only because YOU know you made a change. I am N55 X3, so the rest of this will be formatted as such.

Hopping out of a stock X3 into a catless X3 in a blind taste test would prove that it's incredibly hard to tell in-cabin under cruise/normal operation.

I do not notice a smell in-cabin, nor with the windows down. I DO notice a smell any time I open the hatch or when I am in reverse with even just one window down. I also notice a smell when outside the vehicle on a no-wind day, but always smell it when i am near the rear of the vehicle.

A female that is constantly in my life notices the smell right away when approaching or around the vehicle. She claims it is "obnoxious" but I do not feel the same, so I feel that this is subjective to the end user.

[ky0u]

Those with Catless DPs that dont notice significant sound differences inside, are y'all running your secondaries still or are those gone too? I'm about to make the switch but I deleted my 2nds last year so I was curious

[anjuna]

Originally Posted by ky0u

Those with Catless DPs that dont notice significant sound differences inside, are y'all running your secondaries still or are those gone too? I'm about to make the switch but I deleted my 2nds last year so I was curious

I am half-F half-E with no secondaries. See my post above yours for clarity on my experience.

[Kevin39]

I have no cats and no resonators, just stock mufflers with the golf tee mod. Cruising down the highway, the sound difference isn't that notifiable to me. Zero drone at all. I think it sounds great and not obnoxious in the least when you get on the throttle.

[ky0u]

Originally Posted by anjuna

I am half-F half-E with no secondaries. See my post above yours for clarity on my experience.

Great!! I saw your post but I hadn't been sure if the secondaries were gone as well initially. Definitely good to know thanks!

[anjuna]

Originally Posted by ky0u

Great!! I saw your post but I hadn't been sure if the secondaries were gone as well initially. Definitely good to know thanks!

The one thing to be conscious of, though, is how your exhaust flap is controlled.

I definitely notice the exhaust note drone MUCH easier being catless with the flap OPEN. When it is closed, it is very much close to stock.

So if you’ve done a mod to make the flap open always, you may want to reconsider your method. I personally run the flap closed always, except for above 4000rpm, which is where it really makes a difference.

[E92only]

If you're located in socal I can give you the irl sound. I'm kittyless with a PE exhaust and MHD tune.

[renzo335i]

minimal difference in sound inside the cabin

[Turbod]

Not reading everything everyone else has posted so far. xDrive has secondary cats so the car is a little bit louder than when the valve is open but not bad at all. The smell difference is very minimal due to the secondary cats. For people reading this without xDrive, the cold starts are decently loud and the car under WOT from the back is loud but inside the car is just loud enough to be enjoyable. Obviously if you have no cats there will be a smell but you'll only notice when stationary for a period of time, more so when the windows are down.

[GEE90]

Originally Posted by Turbod

Not reading everything everyone else has posted so far. xDrive has secondary cats so the car is a little bit louder than when the valve is open but not bad at all. The smell difference is very minimal due to the secondary cats. For people reading this without xDrive, the cold starts are decently loud and the car under WOT from the back is loud but inside the car is just loud enough to be enjoyable. Obviously if you have no cats there will be a smell but you'll only notice when stationary for a period of time, more so when the windows are down.

Definitely agree here, I have 2011 E90 N55 X-Drive with CTS downpipe and muffler delete. The smell is not too bad daily driving with the windows down most of the time. The only time you'll really notice it I'd say is if backing into the garage since all the fumes are going inside. Other than that smell is not really an issue.

[GEE90]

I'm kind of debating switching my exhaust set up though, I'm used to the average smell of catless dp and I'm wondering if I were to put my mufflers back on and take out my secondaries with straight pipe if there would be a huge increase in smell. I don't really care about the sound difference but I'd assume it would be a little bit quieter too?