An X-Pipe is, you guessed it, shaped like an x, and allows the exhaust to flow down the path of least resistance. At lower revs, turbulence is formed as exhaust gases try to shuffle past a second column of gases coming from the other side. While always producing more power than the restrictive factory system, the potential gains are not seen until higher rpms are reached. This is where an X-Pipe stands apart from the rest. Exhaust gas is pushed out harder as the engine spins faster. The X-Pipe merges this chaos into two uniform streams, allowing a smooth flow from engine to tailpipe.
Both streams keep each other up to speed, which draws even more spent exhaust out the cylinders. X-pipes provide a boost in horsepower and a higher tone akin to an exotic car.
An H-Pipe is also shaped like its namesake and relies on exhaust expansion to balance the cylinder banks. A small section of tubing in between the main pipes provides an area for gases to expand into during exhaust pulses. Only a small amount of exhaust flows from one stream to the other as both sides push back and forth in the center section. H-pipes feature low restriction, so gains in performance are noticed from low rpm and give the exhaust a deeper, muscle car-like tone.
While both X and H pipes serve the same purpose, they use different methods to build power and economy, all while providing a distinctive sound. Think of an X-Pipe as being at home in a high-winding modern V6 or V8 while an H-Pipe conjures memories of tire-shredding torque in classic American iron.
From a pure horsepower standpoint, the X-pipe will always make more horsepower than an H-pipe will. That does not mean the X-pipe is the right choice for your vehicle application. If you have a lower performance engine, or an engine that does not have a lot of compression, you may find that you put the X-pipe on and it makes more peak horsepower all day long, but it doesn’t mean that the vehicle is going to perform better because it lacks backpressure now. The loss of that backpressure will hurt low-end performance, so the torque and the acceleration of the vehicle will then lag, and you will find that the vehicle then got slower. It doesn’t mean it isn’t making more power; this just means it’s not producing the power where it needs to be produced in that engine combination.
Many ask if the best spot to mount an X-pipe or H-pipe section is up front just behind headers (or exhaust manifold), toward the rear in front of mufflers, somewhere in the middle, or anywhere there's room. Exhaust system experts say the best spot to put your section is generally toward the front of the exhaust system near the transmission.
Old-school racers swear by a crayon trick to find the exact optimum point in the system. What they do is use the crayon to draw a thick, waxy line along the whole length of the exhaust system. After heating up the exhaust system by taking a short drive, an inspection of the system will let you see where the crayon wax stops melting. Whatever spot that may be, that's the optimum place to start your section. Others say if space is tight or the underbody of your vehicle doesn't allow placement in the optimum spot, mount the X- or H-pipe wherever it's realistically possible. You may lose a slight bit of performance by doing so, but you'll still gain compared to not having a crossover exhaust section at all.
Here's some more to read. Has pix too!
http://www.superchevy.com/how-to/ex...y-horsepower-but-which-is-best-for-your-ride/
