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 Post subject: X pipe question
PostPosted: November 29, 2017, 12:51 am 
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Toyotaphobe
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Location: Fort Worth, Texas
I'm helping a buddy stick an engine where it doesn't belong and have a question about placement of an X pipe in the exhaust.

The traditional position is after the cat and before the exhaust, but he's trying to keep exhaust extra quiet and mellow so he wants to put the mufflers after the cats and the X pipe afterwards. To me it seems that the X pipe serves the same purpose no matter where it's located in the system. Am I wrong - AGAIN?

I know from experience that the more pipe you have after the muffler the less harsh is the sound.

I have learned the X pipe also helps with the sound as well as smoothing out the power. I don't know why "balancing" the exhaust does that (balancing is what most people say the X pipe does), but in this case just making a better, smoother sound would be worth putting it in.

So what do you geniuses have to say?

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 1:16 am 
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Joined: June 8, 2010, 8:02 pm
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Location: White Rock, BC, Canada
Sound waves are just that, a wave. The difference between the highs and lows is what makes it loud. If you take an identical noise, and play it timed so that the highs overlap the lows of the other wave, they will cancel each other. (Imagine a speaker getting two signals once per second. One at +5V, one at -5V. It's not going to move). Also, exhaust is not a steady noise but pulses. So if you add more pulses to fill in the gaps it sounds smoother.

https://www.youtube.com/watch?v=fCio5K0WfHU&t=904s

I've never seen an Xpipe after the mufflers. I expect it would be best used before the cats and it's only packaging/emissions that puts it rearward of the cats in typical cars. (Edit: I say before cat is best because, if done right, should take the large peaks out making the mufflers have to deal with less. After the cat and mufflers, the sound waves/pulse are broken up.)

Cheers.

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 3:21 am 
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The only X pipes I've seen are installed after the cats and before the mufflers.

We were scratching our heads tonight and realized that a 2 in and 1 out muffler would simplify routing, but would that be as good as, or maybe the same as, an X pipe?

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 5:46 am 
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As a point of reference:

We just stuffed an H-pipe and twin 31"x2" glasspacks in my brothers truck, which is a MightyMax with the Mitsubishi 3.0 V6.

We put the H before the mufflers, no cat. Tubing size of 2.25", dual to the back.

Previous system was a Y into a single glasspack of about half the length of the replacements.

It's louder with the duals than with the single, a bit less drone, and slightly raspier at the higher end of the rev range.

It's missing the boat burble that it had when we ran it without the H with open headers.

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 5:55 am 
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As I recall, the stated purpose of the "x" or "h" pipe is to balance the exhaust for better scavenging of the cylinders. Better sound is just a side benefit.

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 11:38 am 
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Ideally you want the X or H right where a painted stripe burns off the header collector. The challenging part is there is usually transmission right there, so you end up putting it where it fits. X and H smooths out exhaust pulses through the tubes, which aids in scavenging, and also tends to smooth the exhaust note, the X being the smoothest (but more work to fabricate).

Magnaflow (and others, I'm sure) have a dual-in-dual-out muffler with an X inside which makes it easier, but placement OF that muffler can be an issue depending on your ground clearance.

Engine Masters (YouTube Motor Trend channel) did a dyno test of true duals, H, and X pipe. X made the most power, but only marginally better than an H pipe. True duals sounded the rawest.

I did an X pipe on my daily '77 C10, and I'm not sure it was worth the effort, but it's done.

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 12:07 pm 
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Serendipitously I found the answer to my question on another forum talking about an exhaust on a different V6 engine.

This is from a person who works at Dynomax.

"No problem. I might just know a thing or two about the Dynomax VT passive valve muffler :P"

"If you want the higher frequency exotic V6 sounds, you need to combine the banks in some fashion, preferably an X or a Y. Think of the difference between a Cobra or early Vette with sidepipes vs. a modern LS or Coyote powered car with a bank-connected symmetrical exhaust system."

"I would merge into a single 3" tube as close to the engine as possible while keeping the downpipes symmetrical in length. Then run 3" back to a single Dynomax VT muffler. Only running one valve will do more to prevent drone at light load and less total absorptive muffler volume will give you more of that Nissan VQ sound that you want at WOT."

So apparently merging the pipes through a muffler solves several problems. One the sound, two it is simpler, and three it minimizes drone.

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 Post subject: Re: X pipe question
PostPosted: November 29, 2017, 4:38 pm 
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Joined: September 19, 2009, 12:33 pm
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carguy123 wrote:
The traditional position is after the cat and before the exhaust, but he's trying to keep exhaust extra quiet and mellow so he wants to put the mufflers after the cats and the X pipe afterwards. To me it seems that the X pipe serves the same purpose no matter where it's located in the system. Am I wrong - AGAIN?


When exhaust gasses enter a traditional chambered muffler, they (generally) see an infinite volume - going from a 2.5" pipe into a muffler that's 12" x 4" totally disrupts the gas flow. After the muffler, the exhaust pulses are completely different, totally muted from what they were before the mufflers.

An X or H pipe is designed to utilize exhaust pulses on one bank to help scavenge the other bank. Because of this, it needs to happen before the mufflers at a point designated by the engine's characteristics. Software like PipeMax lets you input your engine and cam data and it will spit out recommended placement of the X or H pipe.

A 2-into-1 muffler will not act the same as a properly-place X or H pipe.

Generally speaking, larger diameter exhaust tubing equals a louder exhaust. But larger diameter doesn't necessarily mean more power. For a 300hp engine, dual 2" or a single 3" can flow more than enough to prevent any exhaust restriction. Running larger diameters than that just means it's louder.


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