[PYCg80]

Looking for guidance or recommendations between a mid-pipe only or axle-back only as the first and possibly only exhaust mod keeping in line with OEM+. Price and performance are secondary, my main goals are:

1. Limited modification, bolt-on/compatible with OEM.
2. Sound - moderate increase in volume, deeper while remaining smooth, a boost in volume when driving hard.
3. Reliability!!!! Don't want to do any programming or worry about anything outside of plug and play.

Am I better off with a midpipe replacement, or axle back only to achieve the goals above? If midpipe, how am I deciding between single, Xpipe and equal length?

[Berzerker]

Either a midpipe-only or axleback-only will require you to cut at the midpipe-axleback joining area. This is normal and is also what BMW does to install the first-party M Performance Exhaust. I would put zero concern in that, specifically.

The recommendation is to start with a midpipe since that gives you the most volume change, as you're removing resonators and secondary cats.

It'd be tough to say one kind or another without having you actually listen to them and see which you prefer. Most people like single midpipes the best as it tends to give a more "deeper throaty" sound compared to equal length or X-Pipe (stock midpipe is an X-pipe config).

If you think you may swap downpipes in the future (this can cause warranty concerns so I'd only recommend if you don't care about that), it's recommended to get a resonated midpipe. If you're not going to swap downpipes, you can get unresonated.

As for axleback, that becomes trivial once you get a midpipe swap as your axleback is already cut from the midpipe, it's just a few screws and some hangers and it's off. Many people actually keep the OEM axleback as it does quite a good job at eliminating drone and is already a straight-piped design with valves open. You'll want to add a valve controller.

TLDR: Midpipe first, then decide axleback.

[ratedpg909]

Definitely midpipe first. It makes the biggest difference. I went midpipe, valve controller, axle back, downpipe in that order

[PYCg80]

Berzerker and ratedpg909 - these posts are why this forum is gold. Appreciate the sound and clear thoughts.

I'm in LA, so I think maybe it's time to find some of these meetups and other places to try and get an earful in person. My week 45 build can't get here soon enough....

[OGOverkill]

Anyone have sound clips of the akrapovic Evolution Link Pipe set in titanium with the stock axle back?

I was going to go with AA catted DPs as I don't want a huge sound increase, but think this may be a better route.

[PYCg80]

Follow up questions on single pipe midpipe mod -

(1) would getting a resonated midpipe defeat the whole purpose if this was your only mod and you were looking for sound deepening/volume? Or do aftermarket ones still offer better sound due to increased airflow, different resonator properties, etc.?

(2) do the secondary cat/resonator deletions from changing the midpipe create any regulatory issues down the road (e.g. smog testing, emissions compliance, etc.)? USA, California. Hoping the primary cat staying in place is sufficient if this is my only mod.

[nosbocaj]

Midpipe + valve controller 100%. Then go from there.

[Swest15]

Originally Posted by ratedpg909

Definitely midpipe first. It makes the biggest difference. I went midpipe, valve controller, axle back, downpipe in that order

What downpipe did you go with?

[ratedpg909]

Originally Posted by Swest15

What downpipe did you go with?

Active autowerkes GESI catted.

[Info@mad-us.com]

Originally Posted by PYCg80

Follow up questions on single pipe midpipe mod -

(1) would getting a resonated midpipe defeat the whole purpose if this was your only mod and you were looking for sound deepening/volume? Or do aftermarket ones still offer better sound due to increased airflow, different resonator properties, etc.?

(2) do the secondary cat/resonator deletions from changing the midpipe create any regulatory issues down the road (e.g. smog testing, emissions compliance, etc.)? USA, California. Hoping the primary cat staying in place is sufficient if this is my only mod.

1. No resonated will just smoothen out the tone it will not reduce the volume a significant amount.

2.Technically yes but there is no sensors to check the secondary cat so only a visual inspection would be an issue. Never heard of anyone having an issue before.

[meechy6ix0]

So I’ve heard it mentioned that the stock muffler is a straight pipe design, but I’m confused on this. With the valves open, there is still the opening that leads into the muffler, so how is that a straight pipe? Whatever exhaust goes into the other opening is straight piped, but some of the exhaust flow does go through the muffler.

[Info@mad-us.com]

Originally Posted by meechy6ix0

So I’ve heard it mentioned that the stock muffler is a straight pipe design, but I’m confused on this. With the valves open, there is still the opening that leads into the muffler, so how is that a straight pipe? Whatever exhaust goes into the other opening is straight piped, but some of the exhaust flow does go through the muffler.

With the stock valve controller its only open around 50% so I guess you could say the muffler has the potential to be straight pipe.

When the valve is half way open it does cause some back pressure and forces some of the air through the muffler pipes.

With a valve controller the valves are 100% open so the air flows through the path of least resistance which would be the straight pipe section of the muffler. I won't say no air is passing through the muffler but it should be very little if it is.


The same goes for our axle back

[Berzerker]

Originally Posted by meechy6ix0

So I’ve heard it mentioned that the stock muffler is a straight pipe design, but I’m confused on this. With the valves open, there is still the opening that leads into the muffler, so how is that a straight pipe? Whatever exhaust goes into the other opening is straight piped, but some of the exhaust flow does go through the muffler.

Actually, neither exhaust opening (taking one side, for example) go directly into the muffler. The valve is actually behind both exits from the exhaust, so when the valve is opened, nearly all air is going directly out.

It's not 100% straight-piped, so there's some air that's going to be backpressured into the muffler, but the path of least resistance is straight through to the outside, most of your air is going to not go through the muffler. Pic attached

[meechy6ix0]

Originally Posted by Berzerker

Actually, neither exhaust opening (taking one side, for example) go directly into the muffler. The valve is actually behind both exits from the exhaust, so when the valve is opened, nearly all air is going directly out.

It's not 100% straight-piped, so there's some air that's going to be backpressured into the muffler, but the path of least resistance is straight through to the outside, most of your air is going to not go through the muffler. Pic attached

Originally Posted by Info@mad-us.com

With the stock valve controller its only open around 50% so I guess you could say the muffler has the potential to be straight pipe.

When the valve is half way open it does cause some back pressure and forces some of the air through the muffler pipes.

With a valve controller the valves are 100% open so the air flows through the path of least resistance which would be the straight pipe section of the muffler. I won't say no air is passing through the muffler but it should be very little if it is.


The same goes for our axle back

Ah, I was thinking the flow going into the muffler route was more restricted but didn’t know it had that much of an effect. That’s awesome to hear! Thanks for the explanation!

[mike@x-ph.com]

I'd start with a single midpipe + sst valve controller

[tom @ eas]

Originally Posted by PYCg80

Berzerker and ratedpg909 - these posts are why this forum is gold. Appreciate the sound and clear thoughts.

I'm in LA, so I think maybe it's time to find some of these meetups and other places to try and get an earful in person. My week 45 build can't get here soon enough....

IMHO, the Evolution Racewerks Midpipe + Awron EVC is the perfect combo. Instant attitude at the press of a button while keeping that OEM+ appearance from the outside.

[Info@mad-us.com]

Originally Posted by meechy6ix0

Ah, I was thinking the flow going into the muffler route was more restricted but didn’t know it had that much of an effect. That’s awesome to hear! Thanks for the explanation!

It is but the valve being half open or semi closed changes that. This is why people are spending big money on valve controllers.

[PYCg80]

OK this may have been answered somewhere else, but instead of reading 6,234,342 posts, I bet someone here has the answer:

Is there a way to modify the valves so the OEM/valve control in the center console is retained, but still get the benefits of the aftermarket controller's full open functionality?

[tom @ eas]

Originally Posted by PYCg80

OK this may have been answered somewhere else, but instead of reading 6,234,342 posts, I bet someone here has the answer:

Is there a way to modify the valves so the OEM/valve control in the center console is retained, but still get the benefits of the aftermarket controller's full open functionality?

Yes, that's the Awron Smart CanFlap Exhaust Valve Controller:

▀▄ eas | AWRON - Smart CANFlap Exhaust Valve Controller for BMW
https://g80.bimmerpost.com/forums/sh....php?t=1991762

[darkforest]

Regarding the discussion on valves and muffler function, so single midpipe with valve control set to fully open should sound the same on stock vs aftermarket mufflers? Since they are both acting like straight pipes with valves 100% open?

Im deciding on whether axle back is worth it. I have a MAD single with SST valve controller.

[ratedpg909]

Nah it won’t sound the same. I had the valve controller and midpipe first then added the axleback. It was noticeably deeper with the axleback and less burbles at lower speeds than stock. It wasn’t much louder at all.

[Berzerker]

Originally Posted by darkforest

Regarding the discussion on valves and muffler function, so single midpipe with valve control set to fully open should sound the same on stock vs aftermarket mufflers? Since they are both acting like straight pipes with valves 100% open?

Im deciding on whether axle back is worth it. I have a MAD single with SST valve controller.

Well like I mentioned, and from what you can see in the pic, there's still some air that's going to go through the muffler, probably 80/20 or something around there.

A third-party muffler will also have smaller silencers, maybe thicker or thinner pipes from the midpipe, different thickness of the walls, different shaper, travel distances for the air, etc, etc.

There's a lot of changes that can be done with an axleback swap. What the OEM axleback does a good job at is reducing/eliminating drone while not decreasing the sound all that much because of the flaps-open state being *mostly* straight-piped. A valve controller, as you have, gets you fully opened valves too, completing that kind of "setup"

If you want a bit more volume with more things like pops/burbles to be more pronounced, an axleback swap might be worth it, but you really should try and find one to listen to so you can compare. Try checking out your local cars & coffee.