Any exhaust crossover--"H-pipe" or "X-pipe" (even the exhaust crossover in non-Vortec intake manifolds, to a limited extent) promotes lower exhaust restriction by allowing the exhaust streams from both cylinder banks to share muffler volume.
It's like the difference between a dual-plane or single-plane intake manifold--a dual plane manifold has the carb sides independent, a single-plane allows more flow through the carb because both sides of the carb are shared by both cylinder banks. An "H-pipe" or "X-pipe" is like cutting a slot between the planes of an intake, allowing a limited amount of sharing.
Allowing the exhaust for the two banks of cylinders to communicate not only
lowers the sound level, it can change the tone as well. Some folks really hate the way an "X-piped" exhaust sounds. Some folks really like it. The real benefit, however, is the reduction in back pressure that the crossover ("H" or "X") provides.
Not
nearly that simple. Note that the Craftsman race truck pictured in this thread--which runs at high RPM--has an H-pipe.
Note the "H-pipe" on a high-rpm "race truck".
That makes me moist. I've had a Truck-Arm-coil-spring fetish for decades. Even considered adding a Truck-Arm rear suspension to my El Camino.
Most folks don't understand that the Truck Arm coil spring rear suspension was almost universally used in NASCAR (and the Craftsman Truck racing series) for DECADES; but it was
standard equipment on Chevy and GMC 1/2- and 3/4-ton pickups starting in 1960. I don't know when it went away in favor of ****** leaf springs again--certainly for the "new" trucks in...1972? I think they were selectively putting the leafs back under the pickups earlier than that, though.
Buddy of mine ran a '68 or '69 GMC 1/2-ton with the Truck Arm ass-end. He bought some cheap Add-A-Leaf "overload" springs, and was very surprised to find that he had coil springs back there, instead of leafs.
The '60 2wds had torsion bar front suspension, too. Again, that got dropped and was replaced with coils after a few years. Even the big trucks had torsion bars up front for awhile in the '60s. There were complaints of excessive suspension wear, and it all went away again in favor of conventional crap.
https://www.curbsideclassic.com/cur...olet-pick-up-trucks-the-first-modern-pick-up/