Raspy exhaust between 3-4K rpm

[jsnppp]

I've read what feels like countless threads on this. Our 318is has a crappy rasp between 3-4K. I've crawled all underneath looking for a loose heat shield or bracket and no luck. Sound appears to be coming out of the exhaust itself.

It's a new bosal exhaust (I believe that is the brand, need to check, wasn't high dollar but wasn't free either) from the cat back. At the same time I put in a new cat.

Even though it's all new, it sounds the same as the ratty rusty one we pulled off.

Any thoughts? Or any recommendations for a muffler that works?

I know this is highly car specific but thought I'd throw it out there... Thanks in advance!

Jason

[roguetoaster]

How old are you? I ask as the M42 exhaust started to get annoying to me in that range when I was about 25. It only got worse when I added a Stromung. I also felt, as did my E30 friends, that the exhaust sounded about the same as my old stocker.

If you want to fix it you'll need to add a resonator. I suggest cutting a section of pipe out around 20", adding flanges and adding a 16" resonator. Probably an even better solution might be two smaller resonators in line. Clearly there is science involved in dialing out resonance, but you could just make a modular section and try a few options.

[jsnppp]

Ha ha ha - I'm 54! I actually don't mind a bit of a rumble, but what we have is a crappy tin can vibration noise that hurts the ears. Its sounds cheap, broken and well rice-y. Only 3-4k. Other than that it's actually nice.

Hmmm, I didn't think about a resonator. I'll look into that. I'm assuming between the cat and the muffler, I need to look underneath to see where there is space and can weld it in. I'll look into flanges too.

Any thoughts on a resonator brand? I think it's a 2" pipe but need to check, but a quick search on AMZN yields something like this: https://www.amazon.com/Universal-Res.../dp/B07NY4Y7NV

Supersprint muffler is nice (I see multiple threads on this) but pricey for sure: https://www.pelicanparts.com/More_Info/SSE3024715.htm I'll probably go resonator and see where that gets me...

Thanks for your reply.

[roguetoaster]

Ha ha ha - I'm 54! I actually don't mind a bit of a rumble, but what we have is a crappy tin can vibration noise that hurts the ears. Its sounds cheap, broken and well rice-y. Only 3-4k. Other than that it's actually nice.

Any thoughts on a resonator brand? I think it's a 2" pipe but need to check, but a quick search on AMZN yields something like this: https://www.amazon.com/Universal-Res.../dp/B07NY4Y7NV

Yeah, the that resonance noise did begin to be uncomfortable for me after 45 minutes or so on the highway. Fortunately, having "upgraded" to an M40 car it does not suffer from such a frequency.

I think the piping is listed as 55mm, so using 2 or 2.25" pipe stuff probably works fine. As to brand, it's a simple expansion chamber, so any inexpensive unit made of decent material should be okay.

[jsnppp]

I'm wondering too if anyone knows of a OEM or near OEM replacement muffler for the M42. PN 18129068568. OEM is available but pricey at ~$500.

https://www.ecstuning.com/b-genuine-bmw-parts/rear-muffler/18129068568/

Jason

[roguetoaster]

How about an ANSA BW6607, it's on RockAuto for $200 and $35 shipping, at least to me. You do need to clean and paint that exhaust if you want it to last since the material is inferior to OE, but it'll work just fine, and I'd bet that the sound is similar to your Bosal, which by extension is probably similar to OE.

I'm not sure I'd just buy another OE type muffler of course.