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DANIEL TINDER (10/6/2008)
Re: the original tread (H-pipe/exhaust tone);
I'm surprised no one mentioned the intake manifold crossover passage. Just restricting it slightly with a truck gasket produces a noticeable change in exhaust tone/volume. Unfortunately, any increase in power that might be expected from a wide open passage (as from the "H" pipe) would likely be nullified by the higher manifold/mixture temp?The addition of a H-Pipe into the exhaust system will reduce the ‘per side’ exhaust pressure which in turn would reduce any tendency for the exhaust to be using the crossover in the intake manifold as a pressure release. With this in mind, the intake manifold can potentially see a slight drop in temperature with the installation of a H-Pipe or anything else in the exhaust system that would alleviate some of the exhaust back pressure.
  Lorena, Texas (South of Waco)
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Dan, If I understand you correctly, you're asking if the crossover would act the same as an "H" or "X" pipe? It would but the crosssection is so small that it wouldn't have much effect. And, as you mentioned, opening it will raise the intake floor temperature. This isn't necessarily a bad thing in the midwest, in cold weather, but hurts on the dragstrip. The "X" pipe seems to be the best on a dyno, while the "H" pipe is easiest to install. Both help.
Frank/Rebop Bristol, In ( by Elkhart) 
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I wonder if there isn't some misunderstanding of how tuned exhaust systems work. I see people using the term 'backpressure' to describe flow characteristics in exhaust pipes.
My understanding is that when an exhaust system is properly sized, the exhaust gas pulses from the cylinders will actually cause a negative pressure wave to reach the exhaust valve when it opens. Of course, this negative wave will scavenge exhaust gas from the cylinder and improve power.
Exhaust pipe size is selected by engine size and cam characteristics. If a cam is tuned for power in the 2000-4000 RPM range, the exhaust pipe should be tuned for that RPM, too.
There is a formula somewhere on the 'net that helps pick pipe size. I think that 1 7/8" or 2" is good for 292's. Things like exhaust crossovers also have an effect.
Also, my Mustang V8 came from the factory with different sized mufflers (and an exhaust crossover). The different sized mufflers prevents harmonics from developing between the mufflers (causing a 'droning' sound at certain RPMs).
Also, Vizard's work reveals that the size of the crossover pipe should be smaller than the exhaust pipe. Finally, the tailpipes should be smaller than the exhaust pipes.
But I might have that wrong.
Best regards,
Paul Menten
Meridian, Idaho
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