Has this exhaust been modded?

[tadmcmichael]

New to the forums and I need some help! I bought a "like new" 2013 M3 with 1,600 miles on it. The car looks perfect in every way, but it does seem loud compared to other M3.

Looked through the diffuser and it looks like the top of the exhaust was opened and then welded back down.

1. Is this the "ACM OEM Exhaust" mod?
2. Should I be pissed seller did not disclose? Car is as stated otherwise.
3. I wasn't specific, but just asked seller if the exhaust had been modded. He said the "dealer had adjusted the baffles prior to delivery." I asked what was involved with that and he said "it was as easy as tightening a screw inside but don't hold me to it." Apparently he can play dumb even better than I can.

I bought off the internet, but I think it would have been highly unlikely I would have noticed this had I bought the car in person.

Sorry the picture is upside down, but it flips it no matter which way I attach it. Thanks.

[JsL]

Take a video of it revving. People on here can tell you quickly if it's Stock, ACM Mod (bypass) or OEM Mod (perforated pipe).

[tadmcmichael]

Thanks. Will have to do that tomorrow, as it will wake the kids (thanks to the loud exhaust!)

As best I could tell from the other threads, the "perforated pipe" had the center section cut out and modified and the ACM Mod had each side opened?

[msan]

Originally Posted by tadmcmichael

Thanks. Will have to do that tomorrow, as it will wake the kids (thanks to the loud exhaust!)

As best I could tell from the other threads, the "perforated pipe" had the center section cut out and modified and the ACM Mod had each side opened?

You are correct

[JsL]

Originally Posted by tadmcmichael

Thanks. Will have to do that tomorrow, as it will wake the kids (thanks to the loud exhaust!)...

You probably have ACM Mod. Does cold start shake the house and you can "feel" the rumble?

[tadmcmichael]

Originally Posted by JsL

You probably have ACM Mod. Does cold start shake the house and you can "feel" the rumble?

I will put it to you this way. The current exhaust has a very low WAF (Wife Acceptance Factor). Especially when I start it.

It does sound like a Messerschmitt barreling down the road though. Definitely puts a smile on my face when it revs.

Will get out there for a video shortly.

[tadmcmichael]

Give me the scoop here guys:

[NoSHAM3]

Definitely sounds modded to me. As to which method I cannot say as I don't have personal experience with either.

[JsL]

Originally Posted by tadmcmichael

Give me the scoop here guys:

That sounds like an ACM modded exhaust. You are basically running no muffler, as everything is bypassed inside the muffler.

Look at it this way, you've already started your wife off to a loud exhaust, so just get one that's a little quieter and she'll be happy.

[///M Power-Belgium]

Originally Posted by tadmcmichael

Thanks. Will have to do that tomorrow, as it will wake the kids (thanks to the loud exhaust!)

As best I could tell from the other threads, the "perforated pipe" had the center section cut out and modified and the ACM Mod had each side opened?

Oem exhaust mod => Perforated method is opened in middle section .
Oem exhaust mod => ACM is opened on both side sections .
How I know that ?
Because I did the mod. by myself => http://www.m3post.com/forums/showthread.php?t=733817
So I confirm that you are 100 % right That you have the ACM method or straight through wich is also the loudest mod for our Oem exhaust .
Enjoy...

[Helmsman]

Yep. sounds modded. Good for you OP, then you already have it done!

[tadmcmichael]

Yes, I was thinking about an aftermarket exhaust anyway. But....I had also planned on keeping the stock exhaust to turn it back to bone stock. It's much easier to sell a car with no mods.

I'm still pissed he didn't disclose (and about his fairy tail unicorn story of the dealer changing baffles for him). I also feel that the car has lost a small amount of value.

[NoSHAM3]

Originally Posted by tadmcmichael

Yes, I was thinking about an aftermarket exhaust anyway. But....I had also planned on keeping the stock exhaust to turn it back to bone stock. It's much easier to sell a car with no mods.

I'm still pissed he didn't disclose (and about his fairy tail unicorn story of the dealer changing baffles for him). I also feel that the car has lost a small amount of value.

You could easily trade for an unmodded exhaust.

[M3an V8]

Our resident ///M whisperer is spot on with the ACM type method. I have the perforated mod with Remus h-pipe( secondary cat and resonator delete) and it doesn't sound as loud as yours does.

[nick3753]

Originally Posted by tadmcmichael

Yes, I was thinking about an aftermarket exhaust anyway. But....I had also planned on keeping the stock exhaust to turn it back to bone stock. It's much easier to sell a car with no mods.

I'm still pissed he didn't disclose (and about his fairy tail unicorn story of the dealer changing baffles for him). I also feel that the car has lost a small amount of value.

I would be more worried about what else he may not have told you about. As mentioned, you can pick up another OEM exhaust easily for cheap, sometimes for free.

[tadmcmichael]

Nothing else so far except a K&N drop in air filter. I can't even find a rock chip on it. It's exactly what I would have ordered, except maybe the tan interior instead of the red. The red is definitely growing on me though.

When I took it for the first ride, I wasn't like "that exhaust is really loud." It was more like "that's the most badass thing I have ever heard." I just don't like any surprises.

[///M Power-Belgium]

Originally Posted by tadmcmichael

Nothing else so far except a K&N drop in air filter. I can't even find a rock chip on it. It's exactly what I would have ordered, except maybe the tan interior instead of the red. The red is definitely growing on me thought.

When I took it for the first ride, I wasn't like "that exhaust is really loud." It was more like "that's the most badass thing I have ever heard." I just don't like any surprises.

Think the cold start cycle was your surprise .

[Ezio]

I bought a stock e92 muffler locally for 100 bucks. So it's not to big of a deal to go back to stock. In fact your modded muffler is more worth that a non modded one. So you could also sell it.

[tadmcmichael]

Ok, maybe I need to be a little more glass half full on this one.

Probably a much easier sell for my wife to have only heard the exhaust loud as a baseline, versus switching to a loud exhaust later.

[tadmcmichael]

Contacted the seller again and sent him a link from here explaining the exhaust mod. He did seem genuinely surprised that it was a lot more than a baffle change. He seems willing to pay for me to purchase a used OEM exhaust to replace this one. Maybe I could keep the OEM for the street if the wife continues to complain and the ACM for the track.

Why is the ACM so much louder than the perf? If the ACM are equivalent to straight pipes, seems like the perf is also straight pipes although they cross?

[Flea7]

ok, I'm gonna say it....just man up and tell your wife to get ear plugs. ACM mod is not that loud.

[JsL]

Originally Posted by tadmcmichael

Why is the ACM so much louder than the perf? If the ACM are equivalent to straight pipes, seems like the perf is also straight pipes although they cross?

The OEM muffler has four chambers total: 2 helmholtz chambers and 2 resonator/absorption chambers.

Helmholtz chambers help with drone and volume and resonator chambers help with volume and rasp.

ACM mod bypasses all four chambers. "OEM Mod" or perforated pipe mod bypasses the two resonator chambers, but leaves the two helmholtz chambers alone. See diagram from Dinan's website.