Components & Sound Impact

[I6V8]

I currently run a Stromung Muffler on my '89 325is with the rest of the exhaust system stock.

I sounds pretty good, deep, no drone and easy to live with but it's not necessarily what I would consider the best sounding stock M20, which - to me - is this car, maybe a little less loud:

https://m.youtube.com/watch?v=WBYK1CFTWGg

The video lacks detail so I'm wondering if any remaining OGs here can hear what this setup likely consist of. Is it straight piped, Y pipe mid section AND headers?

Another setup that sounds great (similar-ish) to me is this South African vendors equal length header + dual-x pipe exhaust:

https://www.instagram.com/reel/Ct_Yk32xg_j/

Dual x pipes almost never get mentioned for M20s (sound unreal on S65) but what I like is the smooth idle and right amount of upper notes in the mix.

Has anyone here in the US experimented with dual x-pipes?

[hopeful]

I recently got the Turner system from ECS, tbh it sounds a lot like the first one you posted. But there's a lot of drone under 3k.

[varg]

Videos in shops and tunnels... everything sounds way better in shops, tunnels, valleys. When it gets out on the road without the enclosed space altering its sound, that's when you'll find out of it sounds good or not. I haven't figured out exactly why so many BMW I6s sound bad, it appears it's mostly down to OEM unequal length manifolds and unequal length dual tube exhaust systems which are a recipe for the buzz/rasp, as are chambered mufflers.

[Northern]

I don't think there's much in the way of mufflers/resonators in that video. I think either the midsection is straight piped, or the catback is.

[I6V8]

hopeful do you have a sound clip of yours? Would love to hear that idling and revving warmed up.

varg you make a good point about the amplification factor. That said, I know what my car sounds like in a tunnel and factored that in if that makes sense. The sound signature of my car is more muffled in the midrange and higher frequencies.

I remember from my E46 M3 days, the catless headers sounded like they changed the sound in the same direction I'm looking for here (but added rasp and drone).

My problem is that any of the combinations I've heard so far in clips (including headers + full straight pipe) aren't close enough to that first clip to be at least a likely candidate, hence the original question.

Hopefully others recognize what the mid and end section might be.

[McGyver]

Time for a thread jack!

About 2 years ago I picked up a set of RD exhaust manifolds from the 2nd reproduction run. I recently found what appears to be a RD center section designed to connect the manifolds to a cat back. This center section only has a resonator, no cat. It also doesn't have a bung for an O2 sensor.



The car will have a stroker with a cam. It will initially run Motronic 1.3 with a chip tuned for an Alpina C2 2.7, as MarkD thinks its pretty close to my build. The car will eventually run MegaSquirt 2.

varg, as the resident tuning expert, and digger, as the resident engine building expert, I was hoping to get your thoughts/opinions.

How bad of an idea would it be to have the O2 sensor only reading a single bank? I assume its not ideal, but it would be very simple to cut a hole and weld on a bung.

Assuming the O2 sensor should read from both banks, should I try to make a little crossover tube like the stock system? Would it be better to modify the part where the two tubes are welded together at the front to make something like an x-pipe? Would either option have a noticeable impact on performance or sound?

The stock system has a little crossover tube with the O2 sensor in the middle:


Supersprint uses an x-pipe with the O2 sensor coming in from the side:

[varg]

I would not call myself an "expert" though I would use a crossover if practical. In the end all it does is make sure you're getting the average of 6 cylinders instead of just 3 of them which is of debatable importance.

[digger]

that RD centre section looks to maybe have a crossover of sorts where the pipes are welded together longitudinally? i would put the bung there it that's the case. reading off all 6 is better but 3 works if needed