Modified N55 exhaust

[Calvin@Vishnu]

A few days ago, we whipped up a quick 'n dirty exhaust for our n55 135. Nothing earth-shattering and completely conventional. In fact, it's conceptually identical to what we made years ago and still have on our n54 335.

We replaced the factory midpipe and installed a fully divorced dual 2.5" pipes. This removed the stock resonator and 2-to-1 merge:


And we also removed the factory single entry muffler and replaced it with dual 2.5" staight-thru Magnaflow exhausts. The piping was made of mild steel. And crush bent. Mandrel bending would be preferable but, for now, this will work just fine. It should be noted that crush bent exhausts are really quite fine in systems that don't require sharp bends. In the case of our car, the pipes are reasonably straight (no acute angles):



The factory downpipe:

It splits off into 2 outlets so that BMW could still use the same exhaust components they used for the twin turbo n54. We retained this component since it houses the single catalytic converter. We were tempted to go fully catless for testing purposes. But that will have to wait for the time being.

The factory 135 muffler:

Single Entry, dual outlet. The left outlet is open/closed by the vacuum operated actuator. The internal layout of the muffler housing is pretty convoluted. No doubt designed for sound muffling and not for minimum restriction.

Replaced by this:

We decided to go with dual/parallel mufflers since we would essentially be cutting exhaust flow velocity/volume in half. Which basically makes the mufflers more effective both in terms of sound reduction and exhaust flow.

View from the back:

We added some simple 2.75" SS tips and oriented that with a nice gangsta lean. Enough to look a little different while not screaming LOOK AT ME.

Sound:
Very quiet! Using two mufflers instead of one makes HUGE difference. The exhaust growl is a bit deeper in note. Not much louder though. Which is unfortuante since we were hoping for a more inspiring sound!

Power:
It helps! Haven't re-dyno'd the car yet. With the factory muffler, we were seeing 275whp with the factory tune and 335whp with the Procede. I certainly hope we've picked up another 10whp. Should know soon enough

[bryce]

thanks for sharing! i've always wondered why an exhaust like this was never made for the n54. i always thought something like this would provide a different, distinct exhaust note and still provide good power. nice work

[CMSS2000]

Could this be the perfect exhaust?

I was starting to think it would be impossible to run a straight through system on this car on the street, but if it's that quiet now, adding a catless downpipe should make it close to perfect volume without being obnoxious and provide close to max HP too.

Sounds very promising. Do you plan on marketing it?

[Ash83]

thx for sharing

[SlicktopTTZ]

Originally Posted by maxnix

Selfish owners who don't run catalytic converters must be too young to remember LA in the 60s which brought about all the smog control, and inadvertantly, the high perfromance engines we have today.

Think about what you do in case everyone else would be dumb enough to do the same.

No wonder, you live in Austin. =P


So how much do cars contribute to pollution, green-house effect and ozone depletion vs everything else that we do?

You are selfish for using electricity. And heating your water? Are you royalty or something? You probably even condition the air in your home. Store things in a refrigerator/freezer? I bet you even have machines for washing your clothes and dishes. Shame on you, so wasteful. You obviously even support the destruction of mother earth by buying and burning fossil fuels, why don't you buy a bicycle, or at least the most fuel efficient transportation you can find?


Anyway, Shiv, great work on the tune, I love how stable everything is and all the data your box can grab. I suggest getting a N55 c@tless downpipe from AR Design and throwing on a mandrel bend system and then showing us another tasty dyno!

[bryce]

Originally Posted by SlicktopTTZ

No wonder, you live in Austin. =P


So how much do cars contribute to pollution, green-house effect and ozone depletion vs everything else that we do?

You are selfish for using electricity. And heating your water? Are you royalty or something? You probably even condition the air in your home. Store things in a refrigerator/freezer? I bet you even have machines for washing your clothes and dishes. Shame on you, so wasteful. You obviously even support the destruction of mother earth by buying and burning fossil fuels, why don't you buy a bicycle, or at least the most fuel efficient transportation you can find?


Anyway, Shiv, great work on the tune, I love how stable everything is and all the data your box can grab. I suggest getting a N55 c@tless downpipe from AR Design and throwing on a mandrel bend system and then showing us another tasty dyno!

LAWL

[shockin330i]

Originally Posted by maxnix

Selfish owners who don't run catalytic converters must be too young to remember LA in the 60s which brought about all the smog control, and inadvertantly, the high perfromance engines we have today.

Think about what you do in case everyone else would be dumb enough to do the same.

Austin, Texas... LOL

Originally Posted by SlicktopTTZ

No wonder, you live in Austin. =P

I loled. I see your from cc. You should come down to the valley one of these days..

Originally Posted by bryce

LAWL

Texas is all over this page

Shiv and calvin good work guys. I'll be looking for you when I change out the turbo in my n55