[iPredictioNz]

Hello, so I was wondering if its possible to get the high pitch sound from the single turbo i6 or the s55(with AA equal length midpipe) on the n54 without going single turbo.

It is possible to get something like an equal length mid pipe but for the n54?
Why does it work on the s55 but not in the n54(or at least seems to lot work)

Does anyone has a link to buy some piece of exhaust to achive that glory high pitch sound?

Also if its not possible I wana know why, just curious at this point tbh.

[oVeRdOsE.]

I dont have a specific video , but I cross few time to time and the easiest way is a '2 to 1' aka single exit at the downpipes.

so 1 post cat (if you want to keep the smell down) , 1 resonator and 1 single exit muffler.


This is what I'm planning to do, but im single.
So 1-2-1 . HFC, vibrant resonator, and valved universal muffler. 3''.


Now I didn't see any cheap single mid pipe+muffler setup, only custom. Closest one is Cobb, but uber expensive. VSRF is also 1 mid, but 3.5'' and I saw 0 video that make a twin sounds good. Always wraspy unless you change the muffler and add a resonator. But at this point, get the car to a custum shop.

[iPredictioNz]

I get it, its a 2-1-2 setup with equal length downpipes I guess?
Or non equal to correct the unequal length of the 2 diferent outlets?

The mid pipe+muffler+resonator thing its an easy thing for me, I have a really good custom exhaust shop near me.

[bapsespace]

Originally Posted by iPredictioNz

Hello, so I was wondering if its possible to get the high pitch sound from the single turbo i6 or the s55(with AA equal length midpipe) on the n54 without going single turbo.

It is possible to get something like an equal length mid pipe but for the n54?
Why does it work on the s55 but not in the n54(or at least seems to lot work)

Does anyone has a link to buy some piece of exhaust to achive that glory high pitch sound?

Also if its not possible I wana know why, just curious at this point tbh.

Hi, I've been thinking about this exact problem for a while and I'm doing some research on it.

Short answer: Yes, it's possible.

Detailed answer:

S55 and S58 engines make their sound from the difference in length of the two downpipes, which, as Active Autowerke says in their patent (US11248511B2), is between 12 and 16 inches (30-40 cm). The AA mid-pipe corrects for this difference to obtain the high-pitched fundamental note of the engine.

N54 Length Difference: ≈ 4-8" (10-20cm)

I haven't done any accurate scientific measurements so far, but comparing the sound of the N54 to tests on Engine Simulator, and by looking at the two downpipes, this seems to be a good estimate. I'm planning to do a proper 3D scan of the engine and the exhaust to get actual measurements. It's possible to make a mid-section that corrects the length, keeping in mind that the length correction must be done before merging the two pipes in a Y X H pipe, resonator, or whatever.
Ps: The front turbo going to the inner pipe is the longer one.

Downpipes Are Not the Only Length Difference

This part is probably not too important since even AA seems to allow lenght differences after the X-pipe. Still, if you look at the E9x exhaust after the X-pipe, the two pipes take different routes. This time the rear turbo, outer pipe, is the longer one, but being after the X-pipe, it shouldn't matter too much.
At the end, the rear muffler acts effectively as an H-pipe with a long connecting pipe. This again alters the waveform. However, since that tube is also muffled inside, it doesn't interfere much. Also, I wouldn't remove that since that precise length is there to disrupt the stationary waves that occur at specific rpms (aka drone).

Turbo Collectors Minimal Difference

Looking at the turbos, you can clearly see that cylinders 2 and 5 have a shorter path to each turbo compared to 1 3 and 4 6. This makes for a little rasp, according to the simulation, but it's barely noticeable. Also, a key difference from the N55 and B58 is their cylinders are collected immediately to the turbo with cylinders 3 and 4 being the closest. That alters the sound again.

Dual or Single Exit

Single or dual exit makes exactly no difference except for one thing: A single exit means a single, larger exhaust pipe, which means a deeper note. Meanwhile, dual exit means two smaller pipes, which allows you to hear only the higher harmonics (mainly responsible for rasp or noise). That's where resonators are used to get rid of the higher-frequency harmonics. For example, the 2JZ or RB26 with a single exit and resonators at the end produces a nice, clean sound that clearly highlights the engine's fundamental note.

Actually, the RB26 comes from factory with an unequal-length downpipe. There's an aftermarket equal-length option that brings out the natural tone of that great-sounding engine. You can hear the difference here. Close your eyes, and you'll hear a BMW


Why No Companies Make an N54 Equal Length Exhaust?

Possibly for these two reasons:

They don't think there is enough market to justify the development and production investments.
More importantly, the AA patent pretty much states that you cannot use sinusoidal curves to lengthen one pipe of the exhaust to equalize it, as that is their invention... so nobody else besides them can do that.

As for now, the only somewhat similar attempt is this exhaust. However by the sound, this is even more unequal (similar to S55 and S58), but it's now out of production anyway.

Right now, I'm trying to come up with my own solution. If I'm ever able to make it work, I'll make it available to the public if people are interested in having a good-sounding N54.

[oVeRdOsE.]

single and dual exhaust will do a difference in sound.

We work with RWDI engineers for our sound study on massive air handling units on hospitals and labs and air speed because you reduce the total available duct size do a massive difference.

Same will happen on single exit or dual. People will go 3'' or 3.5, while the dual will be 2x 2.25 or even 2x2.75.

the single exit will ''whistle'' way more if less area and more air speed (also more pressure lost ).

I also did not do a wave physics analysis, but based on the report I receive on my HVAC design, I'll assume there's a difference, and you can surely see it on youtube videos.

does not mean you'll get the N55 sound, but it's damn close with a ST + single exit.

[bapsespace]

Today I noticed something really interesting:

As I mentioned before, the two exhaust pipes take slightly different routes after the X-pipe. In particular, the outer pipe, connected to the rear turbo with the shorter downpipe, has a greater length.

Roughly measuring the pipe length difference from this picture, it appears to be around 15-20 cm (6-8 inches), VERY similar to the downpipes differnce.

Could it be that BMW initially designed an equal-length exhaust but ultimately decided to place the X-pipe in the middle ruining it for other reasons?

It seems like replacing the X-pipe with two straight tubes, then merging the pipes where the rear muffler would reside (either with an X-pipe or a single-exit merge) could potentially perfectly equalize the sound.

Like this: