I could not find any post discussing this in the past, but I was bored, so I shoved a camera up my tailpipe (lol).
The m157 mufflers have a no restriction, straight through design. The Inlet pipe simply comes in the muffler makes a slight turn into a ~8' long pipe with ~6" of perforations, then it Ys into the 2 tips and exits.
IMO I don't think a muffler delete or any aftermarket mufflers could increase performance in any way... It would solely be for sound.
Having said that, this opens the door to a "muffler mod" similar to what people have been doing for years on other cars, such as the c6 z06. Simply cut an opening on the top of the muffler, and either replace the perforated pipe with a solid pipe OR easier yet, just put a butt joint clamp over some or all of holes (depending on the desired sound) and then reseal the muffler for a stock, un-molested look.
I could NOT get the camera to go into the resonators, (there was a lip that prevented it) but it appear the first few inches of the resonators are straight, perforated pipe as well. Does anyone with a resonator delete have picture of the inside of their resonator?


Video of muffler Picture of muffler:







Resonator:

 

Thanks for the info!

Your youtube link was not clickable but if you copy/paste the text it works.

 

People with bmw 335s are doing this and are achieving some nice sounding cars for minimal work.

 

Not surprising at all. Great to document.

At higher output levels (for OEM vehicles), the mufflers are usually not that restrictive, and changes are just for sound.

Similar to the Sports Exhaust option for the Porsche 911 (PSE), which is a straight through design with the valves open.

I do prefer the exhaust note of the M156 compared to the M157, miss my C63.

 

I can get a pic of the resonators. They look the same though. Straight thru. Both sets.

 

I figured they were, I was curious if there was any mixing between the sides??

 

Did you use one of those digital borescopes?

 

Yes, one of those cheap Amazon ones that connects to your phone

 

That is one reason why people just delete the muffler and replace it with straight pipe and call it the day!! Definitely you get a lot more V8 roar from it.

 

Yeah, the mufflers on these cars are pretty great already from the factory. I would only replace them with mini race mufflers for a louder sound.