Learn me: Inline 6 exhaust

My exhaust is trashed, full of holes and leaking. 

Going to take it in to get an exhaust system built.

What's the best setup for an inline 6? Dual or single exhaust? 

I do not want raspy

Specs: Naturally aspirated 3.0 24v with 2 exhaust manifolds 

Single

Only reason I would entertain duals is if you had a setup like my truck, with dual manifolds.  Otherwise single is gonna be better flow.

If you don't want raspy use a nice big resonator and properly sized muffler and you should be good. 

BMW S52 cars came with a 6 into 2 with a crossover. Stock they are nice and mellow. Mine is 6-2-1 which I like even more but it's a "bit" louder than stock.

I have an Ireland Engineering exhaust on my BMW M535i.  It has dual downpipes from the engine, running through a two in, two out catalytic converter and two in, two out mufflers.  I think it sounds pretty good and isn't raspy.  It looks like this: https://www.iemotorsport.com/product/stainless-steel-exhaust-system-e28-535i-e24-635csi/

Single, free flowing and K&N.

6-3-1, pay attention to the pairings.

Jaguar E-Types had a fantastic, mellow non-noisy exhaust that just sounded so right......separate pipes all the way to the back, two mufflers, two resonators. Front three cylinders fed into one exhaust manifold, back three into the other.....

Jaguar E Type 61, exhaust sound - YouTube

Think of musical instruments. Two instruments playing at 250 Hz do not sound the same as one instrument playing at 500 Hz.

Do you prefer the sound of 2x 3-cyl or 1x 6 cyl?

preach said:

6-3-1, pay attention to the pairings.

That will be difficult with two exhaust manifolds.

Almost all inline sixes are 6-2-1 exhaust, in part because super long exhaust manifolds crack more easily, and the nice thing about sixes is that, besides being basically split evenly front to rear, having 240 degrees of separation in each half of the engine means that there is no chance for weird blowback effects to occur with one cylinder blowing exhaust into another.

3 cylinder engines sound gnarly like angry sixes, because most sixes are set up as two threes.   I like the 6-2-1 approach with one caveat: Make sure the pipes between the manifolds and the Y pipe are equal length.  This is super important for good sound and why a lot of V6s sound like garbage.

Dual manifolds 

Garrett makes wonderful mufflers for inline sixes

How do you make it sound like a flat six?

VolvoHeretic said:

How do you make it sound like a flat six?

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/1987-e30-coupe-rally-build/143918/page9/

Sitting behind his car in line, it sounded eerily similar to a certain rallycrossing 911.  

And by eerily I mean awesomely

Here is a video I made 20 some years ago and which I just uploaded onto YouTube of what 3 liters of 6 into 2 sounds like. Pretty close to Darth Vader's TIE fighter.

Edit: I misread your original post. So, this is what you DON'T want your car to sound like? I suppose two Cherry Bomb mufflers with 6 into 2 like my brother had on his old 3.8 XK150 Jag is also a NO NO.

"6 into 2 dual exhaust with 2 tiny turbo mufflers which were too quiet until the hanger bolt nut fell off at highway speeds and they ground on the asphalt for a couple hundred feet. Now just right. Filmed with mini VHS camcorder."

preach said:

6-3-1, pay attention to the pairings.

There is no traditional 180° separation pairing of cylinders in an I6.  1 and 6 are 360 degrees apart.  Closest pairing of any two cylinders in the firing order would be 120 degrees, then 240.

I think the slant six and Ford six guys have tried various pairings with the I6 and seem no real improvements. 

Grouping the front 3 and rear 3 is the best you can get, and thats likely how his is already set up.

In reply to Mr_Asa :

Traditional cylinder grouping is simply 720/N, where N is the number of cylinders being grouped. So the traditional 4-cyl in a 4-2 pairing would be 360* (1-4, 2-3) separation. Doing a 6-cyl in a 6-3 pairing would likewise do a less common and more challenging to design, build, and fit 360* (1-6, 2-5, 3-4) separation. Hence the 'pay attention to the pairings' comment. The traditional 6-2 grouping would do be 240* (1-2-3, 4-5-6) separation.

The Goodparts header on my TR6 is 6-3-1 with the 1-6, 2-5, 3-4 pairings.  Richard tested a bunch of arrangements and found that to give the best overall balance.  The autocross car in Virginia had a 6 to 1 header that split into two pipes.  Not the best combo, but it did give very nice high-end power.  Fitting anything bigger than a single 2.25" pipe through a TR6 frame is a tight fit.

Of course, none of this helps yupididit unless he buys a new header.  In his case, I'd go single pipe.

there is only one answer -

So for the folks saying 6 - 2 - 1, where are you collecting from 2 to 1? And what size do you recommend? Resonator or nah? 

Any recommendations on a got cat? I Think mine is pretty much done. 

In reply to yupididit :

1-3 and 4-6 is common on the OEMs, but for full scavenging you might want to go by the first three on the firing order as a group with the second three as the second group.

Gonna be a good mess of snakes.