So I have a 2.5 inch mostly mandrel-bent true dual custom exhaust system on my 5.4L supercharged 2V truck. Stainless JBA shorty headers into a pair of Catco 2200 series high flow cats, through the piping and into a Magnaflow DIDO 11379 4x9 oval 11" body muffler.

At the time of the install a couple of years ago, my exhaust guy's Magnaflow catalog incorrectly indicated that the 11379 muffler had a perforated Tru-X core. In other words there was an X pipe built into it. Well I found out that's not true, as the 11379 11" body muffler is actually two straight through pipes. Only the 14" and 22" mufflers contain the Tru-X core in the DIDO configuration. So I have basically been running divorced true dual pipes with no crossover.

Fast forward to last friday, where I had my exhaust guy install what was supposed to be a Magnaflow 10791 2.5" Tru-X X pipe crossover into my existing system. He spliced it in, rebent one of the pipes to fit, and repainted the pipes black. He said the X pipe might make it a little quieter, and reduce interior drone a bit.

Previous to the X pipe install with the divorced duals, it had a nice aggressive exhaust note but an extremely tolerable level of interior drone. Adding the X pipe to the system alone, it has a louder idle, a less aggressive/more muddy exhaust note, and 3X the interior drone! Holy crap is the drone unbearable. It buzzes through the interior right after take-off, and gets extremely bad in the 1600-1900 RPM range.

What gives here, seems like it works fine for everybody but me? I'm gonna have to have it remodified again and go with an H pipe instead. I thought X pipes were supposed to help reduce drone. And correct me if i'm wrong, but the X pipe he installed doesn't look like no Magnaflow Tru-X to me.

 

New one for me...

 

The X pipe he installed doesn't look like a Magnaflow unit. Notice how it's square-shaped in the center. The Magnaflow Tru-X has defined pipe shapes that intersect at the center to truly look like a X.

I had a Ebay special X pipe that looks similar to the one I just got installed. It had the square shaped center and also droned like a mother. It seems like that square open chamber would promote drone in the same way a hollow open chamber Flowmaster muffler would. And I think it has become way worse in my case since this X pipe is sitting right under the cab of the truck. Without the X pipe it was quiet when you needed it, and loud when you wanted it. Thoughts on my theory?

Here's what a Tru-X looks like (i'm sure you already know)

 

Yeah, I noticed an increase in drone too when going from an H-pipe to the X. I still like the overall tone that the X-pipe helps make.

 

It was not S/C, but my 2001 5.4L NA Screw I installed the Lightning Bassani Dual system on, with the X pipe. Had to cut the factory Y out and change to a system that looked more like the L / HD system with the dump in front of the rear wheel. The Bassani X pipe was more defined in the round X look, rather than a stamped box look to it.

The Bassani X pipe with 2 SI/SO mufflers did not cause cab drone. It was loud at WOT, but at cruising it was mellow.

 

Thanks for the input fellas, keep it coming if you could. I'm leaning towards changing the setup to a H-pipe.

Here's the before/after X-pipe videos if you want to hear the difference the X-pipe alone makes. Watch with headphones for best quality.

Before
http://www.youtube.com/watch?v=CFUi3...&feature=g-upl

After
http://www.youtube.com/watch?v=ZjxyO...&feature=g-upl

 

It seems like with the X pipe the idle and low RPM exhaust note became a bit beefier, but it seems to have lost some of its aggression revving it into the higher RPM's.

What do you guys think, should I just go with an H-pipe and be done with it?

 

From what I recall, the H pipe did not add anything with the scavenging effect, it was only an equalizer.

The other thing, the '03 and older L and the HD had the X pipe right at the front of the dual SI/SO mufflers.

The kit in the picture above is installed as it would be on a L or HD, and the additional pipe is added to the front ( had I got a HD version, the pipe would have been in the kit ).

Don't know if this still holds true on a S/C 5.5L 3V motor or not, just know what I had found out before.

 

Here's my 2 cents....an inexperienced muffler guy.....to find the correct spot to place either an H or X, is to run a small line of paint down the side of the exhaust pipes 9both pipes), drive the truck for 10-15 minutes. Where the paint has blistered is where the "area of confusion" is......meaning that is where to install the H or X. Incorrectly placed when combined with thinwalled pipe (less than 16ga), the reverb(drone) is going to be increased and heard.

 

I think they both sound like crap.................Who would want to listen to that?

 

My X and H sounded identical at idle and low RPM. At mid to high RPM is where the difference was. X is not as choppy sounding, and sounds a little smoother.

Now thinking back, I also had no crossover to start with. The H and X both made more rumble in general over no crossover at all, but to me they sound a lot better than no crossover.

Long story short, I think you will have the same problem with the H pipe.

 

 

Thanks, guy! I know I am old, but regardless of all the CAD engineering, mfg, etc, etc (which is very good- don't get me wrong) sometimes the ol fashion way of doing things may not be "cool" or even "High tech", but it always seems to work when everything else fails.

 

So today I took the truck back to the exhaust shop and had the stamped X-pipe cut out and had a H-pipe section fabricated in its place. They used a short 3" long section of 2.25" pipe flattened into an oval shape to create the crossover between the 2.5" pipes. The crossover is a bit further forward than the X was, and is as far forward as possible which is good.

Interior resonance is still worse than the crossover-less /divorced duals configuration but a bit less than the X-pipe. It is also in a slightly narrower RPM range now. Having a crossover is better than none so I figure i'm going to have to deal with what drone there is. Heck, I may even switch the setup for a pair of SISO Magnapacks down the road who knows

After H-Pipe sound clip:
http://www.youtube.com/watch?v=MojZUhEsKyI

 

Here's a couple of pics of the H-pipe





11379 4x9 11" body DIDO muffler