H-Pipe and X-Pipe Exhausts

Discussion in 'The Champagne Room' started by SRT-Tom, Jan 10, 2022.

  1. SRT-Tom

    SRT-Tom Well-Known Member Super Moderator Article Writer

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    Oct 2, 2011
    southern New Jersey
    Motortrend has an interesting article comparing Flowmaster and Magnaflow mufflers.

    Also in the article, it discusses H-pipes and X-pipe exhausts. Here is an excerpt from it:

    "Whether you choose a Flowmaster or Magnaflow muffler, either will benefit from some type of crossover pipe, and here's why. In a V-8 engine, the firing order from bank to bank does not always alternate, but repeats. This is to help compensate for crankshaft/bearing loads and balance concerns, and it means that cylinders on the same bank often fire consecutively. For example, in a small-block Chevy, cylinders five and seven are consecutive, as are four and eight. With all Ford V-8s, it's cylinders four and two, and seven and eight. Classic Mopars are eight and four, and five and seven. The Gen III Hemi fires four and two, and six and five consecutively, and even an LS (the engine with the least to gain from an exhaust crossover) fires cylinders two and six consecutively. At higher rpm, the behavior of these events acts as one longer pulse—a single slug of exhaust twice the normal size that can pile up and cause a restriction. Moreover, as the camshaft's overlap of the exhaust and intake lobe increases, the greater the positive effect exhaust scavenging—and a crossover pipe—has (see this Engine Masters dyno test of crossovers vs. straight pipes on a mild 5.3-liter LS with a 2.5-inch exhaust and a small cam).

    The key to reducing backpressure from these consecutive bank firings is to merge the cylinder banks with a balance pipe—what we call an h-pipe or x-pipe. When an exhaust pulse encounters the crossover, the flow capacity of the alternate bank is shared, and a well-designed balance tube can act like an extra highway lane to relieve backpressure. Here, the type of crossover matters somewhat; a simple h-pipe crossover pays a smaller dividend due to the sharp right angles the exhaust must follow (the larger the crossover diameter, the better), while an x-pipe is better than an h-pipe at higher engine speed because it's like a traffic intersection where no turns are needed. So which muffler is best on an engine with serious power, Flowmaster or Magnaflow? Chances are, it's the one that's attached to a three-inch diameter dual system with an unfettered three-inch x-pipe."

    Magnaflow vs. Flowmaster: Attempting to Settle the Eternal Muffler Debate (motortrend.com)