Equal-length exhaust discussion: new S55 sounds

[aBMWfan]

Originally Posted by rk_titanium

Dual 3” merging to a single 3” and out is less flow than oem on these cars. All sound aside, this design doesn’t add up.
Removing one of the valves is also going to trip your cel unless you’re planning on leaving it plugged in and zip tying it off which is....

I agree. Sorry it needs the merge the dual into a 3.5 inch pipe at least. You don’t want to mess up the flow

[Frode D]

I'm also curious why they don't use 3.5" pipe.
2x2.5" equals 9.8cm2 and one 3" equals 7cm2.
3" equals 9.6cm2...

[doughboy]

Not sure about the maths there?

2.5" dia = 31.6cm2

So 2x2.5" = 63.2cm2

1x3" dia = 45.6 cm2

1x3.5" dia = 62.1cm2

But it won't make any tangible difference to performance.

[Lifestyler]

1x 3" rear can handle easy 600hp.

But when i would build this I do sure 3.5 after The Y.

[e28bimmer]

Stock pipes are 2.5in so this can't flow any less than stock. You have to keep in mind that exhaust flows in pulses not constantly, and it only pulses once at a time so taking 2 2.5in pipes merging in to one 3in pipe will not cause an exhaust restriction. This is not "the most HP possible" exhaust system, if you want the most hp possible then sound quality gets put to the wayside. This is a sound quality setup, which by the design, is very unlikely to have a negative effect on hp. Dyno numbers will show in time I guess...

[Frode D]

Originally Posted by doughboy

Not sure about the maths there?

2.5" dia = 31.6cm2

So 2x2.5" = 63.2cm2

1x3" dia = 45.6 cm2

1x3.5" dia = 62.1cm2

But it won't make any tangible difference to performance.

Sorry, I was mixing inches and centimeters.

[Flange]

Originally Posted by DansM

Is the solution to a better exhaust a set of instructions from people to take it to an exhaust shop? Or is there an actual replacement being fabricated and sold?

Hopefully this time next week, Milltek will have something they’ll be able to produce for sale....

[RMDZidane]

OEM exhaust is ~65mm, or ~2.55in.
.....just sayin'

I'm with ntg on the sound being worth it. I have fast cars, my wife's F80 M3 is not really one of them so a slight decrease in hp is not making a difference to me

[MyFragileHalogen]

Performance would still matter for those who track there cars (lap times, 1/4 times). Also if it has to be louder than OEM exhaust setup to achieve it that could be another negative factor. Regardless, pretty awesome what you guys are figuring out.

[spool twice]

unless we have side-by-side dyno's, it's really just guessing. Something tells me it would be negligible since it's a small portion that's technically a crossover point which has a scavanging effect.

happy that more are starting to discuss this however, this is great and will only serve as a motivator for others to join in on development.

[spool twice]

Originally Posted by Lifestyler

We finally made it.

Imo one of the best sounding s55 I have heard.

Car runs catless dps
Full custom midpipe
Paired with MPE titanium muffler

There is a minor tone (at sec. 6) that we don't like, and I already get a solution for to eliminate this.

So stay tuned

#INKEDCUSTOM

I ended up listening to this through my home surround system, this thing sounds epic and actually has Porsche flat-6 tones past that 6 second mark

[Lifestyler]

Originally Posted by spool twice

I ended up listening to this through my home surround system, this thing sounds epic and actually has Porsche flat-6 tones past that 6 second mark

Thx for thumbs up bro.

We figure the noise at 6 sec
Out soon. Solution is already in production 👍

BTW this is in stock mapping, because Winter tires and 600hp not possible to go WOT without wheelspin... 😅

[Judd]

The .5" diameter isn't that much of an issue provided the exhaust is allowed to flow in a more direct direction with minimal deviation to maintain as much laminar flow as possible. Each bend will add an equivalent friction coefficient equal to a straight length of pipe.
For example each 90 degree elbow would add an equivalent friction coefficient of an additional 24" of straight pipe (guesstimates here, I would have to run the simulation for accuracy), multiple bends will disrupt and reduce (turbulent vs laminar) the flow rate significantly more than a 0.5". And yes I do these calculations with fluids/gases on a daily basis.

[Insane435]

Will we be able to get the eq sound using catless downpipes? Does it matter which set of downpipes gets used? I assume all are the same in terms of length

[Lifestyler]

Originally Posted by Insane435

Will we be able to get the eq sound using catless downpipes? Does it matter which set of downpipes gets used? I assume all are the same in terms of length

It's very hard, but IAm very close on a solution, just scroll through the thread and check my progress.

[jpsimon]

This top gear setup replaces the secondary cats, I’d bet that alone will make up for any negligible difference compared to stock.

[doughboy]

Originally Posted by Flange

Hopefully this time next week, Milltek will have something they’ll be able to produce for sale....

Have you had any feedback from them yet?

[SOM_M2C44]

Sounds really good. Love that RB/2JZ sound.

[OGMthree4real]

Subscribed!!

[OGMthree4real]

Originally Posted by ntg44

In the mean time, I recorded a few standing revs. After a couple hundred miles, my exhaust is breaking in really nicely.

Mmmmmmm sooooo good

[GT_Juls]

The wait is really killing me.

[Flange]

Originally Posted by doughboy

Have you had any feedback from them yet?

I dropped the car with them on Friday (7th) so I don’t expect anything until the end of this week / early next.