[BRD1234]

When attempting to do this should I keep the pipe measurements the same or should I change any of them.
My plan was to go from the downpipes to these exhaust flanges that ar design sells to then stepping it out to dual 3" piping then joining that dual 3" to single 3.5" piping all the way to the back of the car (just like hpf).

The only thing i would do differently is just keep the piping straight and not worry about a resonator.
Can anyone give me any input or ideas or tips?
I have a friend who his whole job is strictly tig welding so I was told that all I'll have to do is supply him with the pipes and measurements.

[Dan_335]

I always wonder what the point of merging 2 separate exhaust flows into one is, surely the optimum setup is to keep the two banks separate all the way to the outlet, minimizing the amount of flow disturbance of merging streams?

regardless it sounds like its going to be loud with no resonators...

['___']

Originally Posted by Dan_335

I always wonder what the point of merging 2 separate exhaust flows into one is, surely the optimum setup is to keep the two banks separate all the way to the outlet, minimizing the amount of flow disturbance of merging streams?

regardless it sounds like its going to be loud with no resonators...

More cross section area, less weight and less frictional loss due to less surface area on the pipe walls all create a better flowing exhaust. If you merge the two at a shallow enough angle, there's very little disturbance to flow.

[HeavyMetalRocker]

Originally Posted by Dan_335

I always wonder what the point of merging 2 separate exhaust flows into one is, surely the optimum setup is to keep the two banks separate all the way to the outlet, minimizing the amount of flow disturbance of merging streams?

regardless it sounds like its going to be loud with no resonators...

Historically, inline 6's perform best under a single exhaust system. I really don't feel like getting into the science of it sorry... Performance aside, when you split an inline 6 right in the middle and run a true dual exhaust it sounds like complete shit... aka two 3 cylinder engines running side by side. Part of the reason the 135i and 1m sound so much better than the N54 335i's is because they run a single setup!

[HeavyMetalRocker]

Originally Posted by BRD1234

When attempting to do this should I keep the pipe measurements the same or should I change any of them.
My plan was to go from the downpipes to these exhaust flanges that ar design sells to then stepping it out to dual 3" piping then joining that dual 3" to single 3.5" piping all the way to the back of the car (just like hpf).

The only thing i would do differently is just keep the piping straight and not worry about a resonator.
Can anyone give me any input or ideas or tips?
I have a friend who his whole job is strictly tig welding so I was told that all I'll have to do is supply him with the pipes and measurements.

So honestly there's more to a performing exhaust than just welding some pipe together. Buuuuut if you're going to go ahead and do it, ask yourself what your end power goals are for your car. If you never plan on upgrading your turbos or really breaking the 500rwhp mark then you may find that it works better to use 3" for the full system as the 3.5" can have some serious fitment issues if you aren't precise in running the piping. Also, the HPF system has aluminum spacers that go in various places depending on e90 or e92 to adjust for the 3.5" pipe. As far as the resonator goes, if you want it to sound like a fart then you should probably leave the resonator off. If you want a smoother sounding but equally loud exhaust I would research some 12"-14" racing resonators. They don't reduce power output or volume, they just mask out that raw rasp that you get with no baffling. A resonator is also straight through opposed to a muffler that is designed to reduce noise with chambers and baffling. Let me know if you have any questions!

[Evil///M]

Originally Posted by '___'

More cross section area, less weight and less frictional loss due to less surface area on the pipe walls all create a better flowing exhaust. If you merge the two at a shallow enough angle, there's very little disturbance to flow.

Couldn't gave said it better myself!

[BRD1234]

Originally Posted by HeavyMetalRocker

So honestly there's more to a performing exhaust than just welding some pipe together. Buuuuut if you're going to go ahead and do it, ask yourself what your end power goals are for your car. If you never plan on upgrading your turbos or really breaking the 500rwhp mark then you may find that it works better to use 3" for the full system as the 3.5" can have some serious fitment issues if you aren't precise in running the piping. Also, the HPF system has aluminum spacers that go in various places depending on e90 or e92 to adjust for the 3.5" pipe. As far as the resonator goes, if you want it to sound like a fart then you should probably leave the resonator off. If you want a smoother sounding but equally loud exhaust I would research some 12"-14" racing resonators. They don't reduce power output or volume, they just mask out that raw rasp that you get with no baffling. A resonator is also straight through opposed to a muffler that is designed to reduce noise with chambers and baffling. Let me know if you have any questions!

I feel like the single 3.5'' piping would be easier though because it would be just one pipe to piece together instead of two. As far as the resonator goes Do you know of any decent companies? I've never had any experience with adding resonators.
I was just mainly going for the 3.5 HPF mimic because I really love the sound and tone.

[HeavyMetalRocker]

Originally Posted by BRD1234

I feel like the single 3.5'' piping would be easier though because it would be just one pipe to piece together instead of two. As far as the resonator goes Do you know of any decent companies? I've never had any experience with adding resonators.
I was just mainly going for the 3.5 HPF mimic because I really love the sound and tone.

The Vibrant Performance 12" or 14" seem to be the most popular weld-ins. I think the 3.5" dia only comes in 18" though.

[flinchy]

Originally Posted by ___

More cross section area, less weight and less frictional loss due to less surface area on the pipe walls all create a better flowing exhaust. If you merge the two at a shallow enough angle, there's very little disturbance to flow.

To match twin 3" cross section you'd need more like a single 4" from memory though no? Or slightly larger?

Either way i'd assume it's a bit (but not as extreme) like a v8 where an x-pipe smooths out the flow a bit

['___']

Originally Posted by flinchy

To match twin 3" cross section you'd need more like a single 4" from memory though no? Or slightly larger?

Either way i'd assume it's a bit (but not as extreme) like a v8 where an x-pipe smooths out the flow a bit

Sq rt(((Pi*1.25sq) + (Pi*1.25sq))/pi)=??? Should be a touch over or under 3.5 if memory serves me correctly. Then add in frictional loss due to more surface area and you have a clear winner for flow at 3.5" diameter. And to be fair, I'm still running an AE 2.5" quad setup anyway.

Edit: Who has a twin 3" exhaust?

[flinchy]

Originally Posted by ___

Sq rt(((Pi*1.25sq) + (Pi*1.25sq))/pi)=??? Should be a touch over or under 3.5 if memory serves me correctly. Then add in frictional loss due to more surface area and you have a clear winner for flow at 3.5" diameter. And to be fair, I'm still running an AE 2.5" quad setup anyway.

Edit: Who has a twin 3" exhaust?

Twin 3" flows 46% more than single 3.5"

Frictional loss isn't THAT high (boundary layers and all of all of like 1mm of low flow lol)

Not counting frictional loss... To match the cross sectional area of twin 3" you need single 4.25"

That's also not taking into account the slightly less flow needed towards the back of the car, narrowing could possibly help keep velocity up?

And the fact that twin 3" is massive overkill unless going vargas 3's maybe hahaha

[Tiago@VRSF]

There's Supras and GTR's putting down 1000whp on a single 3.5" exhaust, going any bigger offers no benefits, only weight & cost.

[HeavyMetalRocker]

Originally Posted by Tiago@VRSF

There's Supras and GTR's putting down 1000whp on a single 3.5" exhaust, going any bigger offers no benefits, only weight & cost.

+1

[flinchy]

Originally Posted by Tiago@VRSF

There's Supras and GTR's putting down 1000whp on a single 3.5" exhaust, going any bigger offers no benefits, only weight & cost.

They see gains going from 3.5 to 4" though (good motoiq article on it) even below 1000hp! - even like 700-800 iirc

3.5" is obviously plenty for what any n54 has ever made though haha

[BRD1234]

Thanks to everyone who responded to me and helped me decide on what I'm going to do.
I think I am going to do a single 3.5" all the way back then drop it off to dual 3" out. As far as resonators go I'm pretty sure I'm going to put one in to help cut down on the rasp.


It's about time for my neighbors to start hating me even more when I start my car in the morning at 6:30

[Tiago@VRSF]

Not sure if you've ever driven in an HPF car before but you're gonna hate you if it's your daily lol. The HPF exhaust sounds great from a far but it's the loudest/most droney exhaust made for this platform.

I'd definitely consider a good sized inline muffler.

[HeavyMetalRocker]

Originally Posted by Tiago@VRSF

Not sure if you've ever driven in an HPF car before but you're gonna hate you if it's your daily lol. The HPF exhaust sounds great from afar but it's the loudest/most droney exhaust made for this platform.

I'd definitely consider a good sized inline muffler.

I daily mine and LOVE it!!! because race car... lol I will say it IS loud inside as well though, not as loud as you would expect based on the outside volume though.

[BRD1234]

Originally Posted by HeavyMetalRocker

I daily mine and LOVE it!!! because race car... lol I will say it IS loud inside as well though, not as loud as you would expect based on the outside volume though.

how is it from the inside? I have a friend with a 2013 5.0 Mustang with literally no cats or mufflers or resonators and it causes everything to shake in a 500ft vicinity. I like loud exhaust but not deafening from the inside.

[HeavyMetalRocker]

Originally Posted by BRD1234

how is it from the inside? I have a friend with a 2013 5.0 Mustang with literally no cats or mufflers or resonators and it causes everything to shake in a 500ft vicinity. I like loud exhaust but not deafening from the inside.

Well nothing rattles inside of the car but you definitely cam hear and feel it! It's all relevant man. I have a straight piped harley and my wife says my car is louder. I've played drums and guitar for 27 years so my hearing may be a little biassed lol

[BRD1234]

Originally Posted by HeavyMetalRocker

Well nothing rattles inside of the car but you definitely cam hear and feel it! It's all relevant man. I have a straight piped harley and my wife says my car is louder. I've played drums and guitar for 27 years so my hearing may be a little biassed lol

Is the sound so loud that you cant hear your music playing with the windows rolled up or if you dont play anything that you get a headache?

[HeavyMetalRocker]

Originally Posted by BRD1234

Is the sound so loud that you cant hear your music playing with the windows rolled up or if you dont play anything that you get a headache?

I can hear my music, but I can also hear the exhaust! It's really all relevant man, I can say one thing and you could think differently. As stated before I've played drums and guitar for 27 years man. Heavy Metal, not quiet music, so loud noises don't really bother me that much!

[BRD1234]

Originally Posted by HeavyMetalRocker

I can hear my music, but I can also hear the exhaust! It's really all relevant man, I can say one thing and you could think differently. As stated before I've played drums and guitar for 27 years man. Heavy Metal, not quiet music, so loud noises don't really bother me that much!

I'm just going to do it! If I dont end up liking it I can add a inline muffler or something small untill I make it the way I like it. Time for some fabrication