Doesn't an "H pipe" or crossover pipe also help give MORE low end torque to the engine, as opposed to just using dual straight pipe? That is what I was schooled on, back in the day, for (street) cars.
An H or X was proven to make some extra torque over a straight pipe, but in general not quite worth the hassle by Freiburg/Dulcich/Westec Dyno in an Engine Master video on YouTube. (This was before they put every behind a pay-wall and hardly no-one gets to watch their stuff anymore.)
Found the video on DailyMotion instead:
https://www.dailymotion.com/video/x5s8nr8In short:
Straight pipe - Torque / Horsepower
366 / 363hp
H-pipe370 / 361hp
X-pipe370 / 362hp
