It seems crazy that just by connecting the exhaust pipes you gain 12 - 15 rwhp.

Has anyone slapped in an X pipe and noticed a difference? Could you even notice a 5% increase, or is that something that would only show up on a time slip?

Cant hurt, the only problem I have with them is it seams that I could not get my exhaust up as tight as regular duals, but I also built my own x.

I doubt 12-15 HP per se but an X pipe works wonders accoustically for noise reduction which then seperately but related allows you to run a less restricted muff/pipe dia rearward from the collector flange which WILL gain you HP as any restriction down stream from the header collector flange (collector reducer/smaller pipe dia/quiet muffs) costs power & you're limited by amt of noise you (or the local constabulatory) are willing to tolerate. backpressure/pulse wave tuning is a primary tube issue only & is very critical to achieve an optimized combo EDIT pri tube length/dia

For what it's worth-------one of the car shows on Speed awhile back had some guys from "Heartthrob Mufflers" on & they broached the topic. Their opinion was that a regular cross-over pipe was more efficient than an X-pipe---something to do with reversion......

..Larry Sheppard (Mopar Performance) says for noise reduction only.
..i have read dyno tests on warm small blocks that only gained 12 - 14
Hp with open headers, but i don't know myself.

Punctuation aside, I thought it was an extremely well thought out and written answer It helped me a lot.

Feets you forgot to add something that would contribute to the OP solving his Q. It has taken me months of discipline and very hard work and perseverence for my grammer to evolve to the level that it is at right now . Sorry you're having a bad day but it's not my grammer. I'm a firm believer in an X pipe but not 12-15 HP by itself

I put an X pipe on my gtx with headers, 2 1/2" pipes and the giant 20" case dynomax super turbos and my exhaust is WAY quieter than I thought it would be. I haven't really driven it yet, but at idle and free reving it I am very pleased with the sound. This is on a stock 70 440 with an MP resto magnum cam.
Travis..

The concept is to provide a pulse from each side to aid in extraction & flow, similar to 180-degree headers. Placement, size, etc affect its efficiency, but if you've ever run a car with an H and then an X, what I noticed is the "smoother" exhaust note, and they make the RPM sound higher than it is. Everyone's "mileage" seems to vary with them, probably because of packaging/size/application variances; I'm not aware of anyone losing ET/MPH from one, but several people have claimed improvements. Hard to quantify though without a lot of data, and that's been hard to come by.
They do have an amusing side-effect though: even at only 6000 in the water box, most people will back away from my car, with concerned expressions on their faces; usually someone will come up to me later to ask if I'm turning 8,000 in the water and what my shift points are.

Thanks for the replies. I actually dont want it any quieter than it is now with headers, muffs (not sure what brand) and 2.5" exhaust. My only concern is getting more power, within reason of course. It sounds like I'm already there and will put the $500+ into the motor.

After running TTI 1 5/8"-1 3/4" step headers for a year or two with just collectors, I installed their 3" X-pipes ending with Dynomax Ultraflows at the rear housing. Overall, it added about 70 lbs. But after getting the overall weight back down and a little carb rejetting from the best I was able to get before, the car was at least .05 faster, possibly closer to .10. So it all stayed on despite being inconvenient for trans or center section swaps. I may eventually go to the Dynomax bullet style to save a little weight and gain a little room around the rear end yoke. (That will allow me to use more easily removable weight if I need move to the next lighter class.)

I didn't do back-to-backs afterwards, but I felt that the mufflers didn't hurt at all and that the X-pipe definitely helped. I can't help but think that each side actually helps scavenging from the other side through the "X" with the alternating pulses. (Just speculating why it helps. I guess basically what topside said.) I installed them as close as I could to the headers with the "X" directly under the very end of my 904 trans.

It works for Nascar! But each combo will have it's own results and may require a little jet tuning for best results.

I run the TTI stepped headers on a built 340 and just installed a X-Pipe with flow Masters and it made a nice difference. The car still has a nice growl and with the X-Pipes and the Flow Masters, I now run the same times in the 1/4 mile that used to run with open headers. It's tough to put a HP number to it, but with my setup I would say the 10 to 15 HP gain is reasonable. If you do go with the X-Pipe setup bear in mind there are several ways of doing it. The pipes can literally cross, or you could also cut a section out of each pipe and have them joined for a few inches, but still maintain the separate pipes.

Yes there is a gain H pipe gains more at low RPM and the X at high so it really is tomato tomato!
But do it!

We! Don't, "need" no... 'Punctiation!. Just messing with you Rapid Robert! I read your posts just fine. (maybe an NE thing?) Most studies have shown an improvement, wether utilizing x or h pipes over a straight dual exhaust. I don't have any data to back that up. Just scads of articles I read about the subject. Maybe contact TTI or other exhaust specialists, and see what they have to say?

It should also be said that all X-pipe designs are not created equal. Most are just jump on the trend/copycat designs, and some are truly awful. Even slight differences in X-over location, X-over size, angles, they all make a difference. This doesn't even get into some manufacturers lazy workmanship.

There was a good thread on this at Speedtalk a while back, and i think the general consensus is that it matters which one you get, where it is put in the system, and how well the rest ov your system is designed and built. The results CAN be good, and 12-15HP doesn't seem out ov reach, but do it wrong, or buy the wrong brand, and you'll quickly negate any benefit or possibly end up with less power.

But... done right or wrong, they sound damn cool, though some people dont like to lose that low old-school rumble. They quiet the system up, which again, some like and others dont.

My Charger picked up serious power going from no X-over 3" press-bend to an X-pipe 3" mandrel. The brand i used was a bad one and i would never use it again. It was cheap, and i got what i paid for. Sounded really mean, even with the junk 440.

My girl's 96GT Mustang went from the stock 2 1/2" H-pipe to a Dr. Gas 2 1/2" X-pipe and the difference was immediate, even going from Borla dumps (on the stock H) to a full Spintech cat-back (on the X). The sounds was/is absolutely glorious... even on a stock 215HP 4.6L.

I highly recommend Dr. Gas. You'll pay 3 times as much as Dynomax... but again, you get what you pay for.

Dr.Gas on my polara which I transferred from my charger years ago.Sounds awesome with the long case super turbo mufflers.