Exhaust gurus: best location for an x-pipe & resonator(s)?

[butters]

I may have the opportunity to go to a custom exhaust for my S50. What I have now is junky, dual & separate all the way back w/crush bends and a single muffler (though that is a nice UUC system U with straight tips). It is way too loud, rough, and drones like no other.

I was figuring to just go mandrel bent SS with a couple resonators, but now I'm curious about X & H pipes and pulse balancing theory, and I do want to be sampling both banks with my O2 sensor. It seems that placement of the crossover makes a big difference, can anyone enlighten me on how to go about choosing a location? I suppose I'm limited by the length of the O2 sensor wire, but my options could be as close as possible to the headers, as far as possible, or somewhere in between. Also do I have the realistic option to go with a crossover and skip the resonator, or would that still be obnoxious?

The other thought I had after seeing some e46 M3 products is that I could skip the X or H crossover and simply merge into a single pipe (acting as a large X), use a larger single resonator, and either get one with 2 outlets or add a split to hook back into my UUC "catback".

Is there any glaring pro/con of X/H + dual resonators vs. merging into 1 and splitting again for the rear muffler? Any suggestions on how long to make the single pipe section, either with resonator length or res+pipe length before a split? I suppose the only real way to know is if research has been done on our inline-6s. I didn't find anything very specific via google and forum searches.

[Supadave]

I'm no expert on gas theory, but I would run a x pipe in the middle of the exhaust system, two resonators and maybe a muffler.

You will want to run your 02 sensor as close to the collector as possible.

Are you N/A?

[The Dark Side of Will]

For 8's, the X should be as close as possible to the ends of the collectors, while being an equal distance from both merges.

However, "end of the collector" is defined by header theory, not by where the joint in the pipe is.

IE, find the collector length that gives you the best power curve and put the X right at the end of it.

Headers by Ed is a good source of "rule of thumb" type header design info. Burns Stainless will spec header designs (primary size/length, collector size/length) for a small fee if you give them some engine data.

[digger]

IE, find the collector length that gives you the best power curve and put the X right at the end of it.

+1

pipemax will tell you this length

http://www.maxracesoftware.com/pipemax36xp2.htm

[Jand3rson]

You don't need an X-Pipe at all on a BMW 24V exhaust system. An X-Pipe is meant to equalize exhaust pressure across 2 separate banks of exhaust outlets. BMW inline-6 engines are configured with 1 single bank of exhaust outlets on the head, hence no need for one.

And resonators aren't going to reduce the volume of your exhaust note, mainly just change the tone. The might alter the decibel level slightly, but mostly what they're going to do is change the tone of the sound.

[butters]

You don't need an X-Pipe at all on a BMW 24V exhaust system. An X-Pipe is meant to equalize exhaust pressure across 2 separate banks of exhaust outlets. BMW inline-6 engines are configured with 1 single bank of exhaust outlets on the head, hence no need for one.

I've done a fair amount of research but I'm not going to claim to be some kind of expert, hence why I'm asking the question. However, I will say that from what I've read pulse tuning and exhaust scavenging do apply to 6-cylinder engines. My headers have, as I'm sure most any inline-6 headers have (in fact I've never personally seen it done any other way aside from the craziness of turbo manifolds... have you seen any other 6-into-1 collectors?) two separate banks. Just because they're next to each other doesn't make them parts of the same bank, in terms of exhaust tuning. I know for a fact that BMW runs an H-pipe in the factory M20 and S54 exhausts. No manufacturer is going to make any addition like that unless it pays back either in sound difference or tuning. If the exhaust is run as truly "dual" all the way back, X & H-pipes do make a difference. I can promise that it sounds junky and doesn't feel all that great if you don't merge the pipes somewhere, because that's what I currently have. I'll have to report back with results once it's all done, there's a good chance I'll get dyno runs before & after.

And resonators aren't going to reduce the volume of your exhaust note, mainly just change the tone. The might alter the decibel level slightly, but mostly what they're going to do is change the tone of the sound.

Resonators most certainly will reduce the volume of drone and can have a dramatic change on the overall volume if they're designed to. I simply need to cancel out some of the aggressive, annoying wavelengths.

[Jand3rson]

Not claiming to be an expert here, either. Just stating what I've been told. Curious to see your results!

[LuckyHenriksen]

I've done a fair amount of research but I'm not going to claim to be some kind of expert, hence why I'm asking the question. However, I will say that from what I've read pulse tuning and exhaust scavenging do apply to 6-cylinder engines. My headers have, as I'm sure most any inline-6 headers have (in fact I've never personally seen it done any other way aside from the craziness of turbo manifolds... have you seen any other 6-into-1 collectors?) two separate banks. Just because they're next to each other doesn't make them parts of the same bank, in terms of exhaust tuning. I know for a fact that BMW runs an H-pipe in the factory M20 and S54 exhausts. No manufacturer is going to make any addition like that unless it pays back either in sound difference or tuning. If the exhaust is run as truly "dual" all the way back, X & H-pipes do make a difference. I can promise that it sounds junky and doesn't feel all that great if you don't merge the pipes somewhere, because that's what I currently have. I'll have to report back with results once it's all done, there's a good chance I'll get dyno runs before & after.



Resonators most certainly will reduce the volume of drone and can have a dramatic change on the overall volume if they're designed to. I simply need to cancel out some of the aggressive, annoying wavelengths.

Amen. Glad to hear someone know what they are talking about!

[smooth]

butters,

what did you ultimately decide to do? I'm in a similar situation and finalizing the exhaust for my 24v swap. I've got a stock obd2 exhaust. I am thinking of putting an x-pipe after the manifolds so I can locate my o2 sensor there. There's an h-pipe after the cats. Not sure if I should leave that be or delete it.

did you figure where the optimal location for the x-pipe would be?

[butters]

because my headers are off-the-shelf and unequal length, I couldn't put much design into the system, and I put the X as close to the manifolds as I could. In your situation I would leave the H-pipe in place, and put the X somewhere convenient for the O2 sensor.