yes this is an old idea and well known, and yes he tried several lengths, the idea behind that is that a sudden change in the exhaust pipe volume, and length, disrupts the pulse frequency and strength, and can generate a secondary frequency that may disrupt the original primary sound/pressure wave, in fact I called the guy up after reading your thread and he said that he had found that mounting the mufflers so one side of the trucks exhausts muffler was mounted slightly further forward that the other side,made even more difference, and the (X) pipe definitely mellowed the exhaust tone, he found that out purely by accident, when he needed to cut out a section of exhaust pipe he damaged backing up into a guard railing, and after making a temporary repair with his friends mig welder just so he could drive the truck, he damaged the exhaust pipe on only one side on a trip to a friends home that was out of state, moving that one muffler about 16" FORWARD UNDER THE TRUCK, and leaving the other were it was, originally mounted under the truck,made a noticeable improvement, the difference seemed to be that now with the total distance being changed by that 16" between, each leg of the exhaust pipe exiting the (X) pipe the frequency on each leg changed enough that it further dampened out any potential drone
To get rid of drone (pipe resonance), you need to cancel out those specific pipe resonant frequencies.
Ive always been amazed at the number of guys who think the only options they have in components , they can use on a car, involve buying and installing parts listed in a catalog. if you have minimal fabrication skills and access to a decent welder your able to fabricate a huge variety of changes and improvements rather cheaply, that can make a very significant improvement in how your car runs and sounds
adding a dual (X) to the exhaust system has proven to reduce the decibel level and spread the torque curve on several corvettes, Ive done that mod to the exhaust on,as it tends to increase the cylinder scavenging efficiency,and reduce the exhaust back pressure, and I read that modifying headers in a similar manor is worth .2-.05 seconds on several cars, so don,t think a bit of thinking outside the box as they say won,t pay off in a bit more power or power over a wider rpm band. thats potentially 5-30 hp gains available due to changes in the exhaust even after you install a low restriction exhaust behind the headers
the use of an (X) pipe located as close to the headers collectors as the space under the car permits like the pipes shown above that feed back to a muffler like the one below mounted as far to the rear as room under the car permits , has been repeatedly shown to reduce drone, and yes on some applications youll want to feed the two exhaust pipes out to two separate low restriction mufflers to further reduce the noise
http://www.superchevy.com/how-to/ex...y-horsepower-but-which-is-best-for-your-ride/
MUFFLERS like this absorb and dissipate much of the exhaust pulse strength
INSTALLING AN (X) PIPE IN THE EXHAUST ON A DUAL EXHAUST CAR
http://pypesexhaust.com/p-13194-dyno-tests.html
Hot rod (oct. 2000)
355 SBC
9:1
trickflow alum heads
2.02''/1.06'' valves
comp
magnum
286 hyd. cam (236/236 deg @ .050'', .490''/.490'' lift, 110 lsa)
edelbrock performer rpm intake
demon 750 cfm carb
3'' dual pipes
flowmaster "big block" mufflers
hooker 1-5/8'' long tube headers
Headers Headers with X-pipe
RPM HP TQ RPM HP TQ HP gain TQ gain
3000 219.8 384.7 3000 231.2 404.7 11.4 20.0
3100 224.5 380.4 3100 235.3 398.7 10.8 18.3
3200 229.7 377.0 3200 242.6 398.2 12.9 21.2
3300 234.6 373.4 3300 252.0 401.0 17.4 27.6
3400 240.1 370.9 3400 262.1 404.9 22.0 34.0
3500 246.5 370.0 3500 271.2 406.9 24.7 36.9
3600 255.5 372.8 3600 280.5 409.3 25.0 36.5
3700 269.1 381.9 3700 290.3 412.1 21.2 30.2
3800 283.8 392.3 3800 300.3 415.0 16.5 22.7
3900 295.5 397.9 3900 308.6 415.6 13.1 17.7
4000 307.6 403.9 4000 317.4 416.7 9.8 12.8
4100 320.7 410.8 4100 326.9 418.8 6.2 8.0
4200 332.6 415.9 4200 337.0 421.4 4.4 5.5
4300 343.5 419.5 4300 345.7 422.2 2.2 2.7
4400 351.8 419.9 4400 352.9 421.2 1.1 1.3
4500 358.7 418.7 4500 358.7 418.7 0 0
4600 362.5 413.9 4600 363.7 415.2 1.2 1.3
4700 367.1 410.3 4700 369.5 412.9 2.4 2.6
4800 371.2 406.2 4800 375.8 411.1 4.6 4.9
4900 374.8 401.7 4900 380.1 407.4 5.3 5.7
5000 376.7 395.7 5000 381.8 401.1 5.1 5.4
5100 378.2 389.5 5100 381.1 392.5 2.9 3.0
5200 380.8 384.6 5200 381.5 385.3 0.7 0.7
5300 383.8 380.4 5300 384.0 380.5 0.2 0.1
5400 387.0 376.4 5400 387.7 377.0 0.7 1.4
5500 390.0 372.4 5500 391.9 374.3 1.9 1.9
5600 394.8 370.3 5600 395.6 371.0 0.8 0.7
5700 397.2 366.0 5700 400.0 368.6 2.8 2.6
5800 397.1 359.6 5800 402.9 364.9 5.8 5.3
5900 393.3 350.1 5900 401.2 357.2 7.9 7.1
6000 388.0 339.6 6000 394.8 345.6 6.8 6.0
peak HP gain 25.0 @ 3600 rpm
peak TQ gain 36.9 @ 3500 rpm
AVG. HP from 3000-6000 rpm 7.99
AVG. TQ from 3000-6000 rpm 11.1
AVG. HP from 3000-4500 rpm 25.8
AVG. TQ from 3000-4500 rpm 17.2
71RS/SS396
