Thread: Exhausting questions

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I'm certainly no expert on the subject, but have thought about it some and tried to make sense of it.

The problem of loading one side or the other of a dual exhaust system has to do with the firing order of the motor. On a small block Chevy, there are two times in the 720 degree cycle that one or the other side gets two shots at a time. In the firing order 1-8-4-3-6-5-7-2, cylinders 8 and 4 fire together on the right side of the motor and load up that pipe while the other pipe has nothing going on in it. Halfway around the cycle from there, cylinders 5 and 7 fire together on the left side of the motor and load up that pipe while the other pipe has nothing going on in it.

If we connect the pipes in some way and allow the two-cylinder exhaust slugs (8-4 and 5-7) a way to disperse into the other (empty) pipe, we can equalize pressure in the system and perhaps attenuate the exhaust note.

I have read that as long as the pipe is ahead of the mufflers, it will work. This makes sense to me. There is little restriction in the system until you get to the mufflers, so all the pipe from the exhaust valve to the muffler would see the same pressure (or vacuum), sort of like in a hydraulic system where the same pressure is seen throughout the system.

As I think about the size of an "H" pipe, I think it should be as large as you could make it (up to the size of the parent left and right pipes) simply because you have TIME to deal with in the system. I would think that a smaller H pipe than the exhaust pipes would take more time to transfer the slightly higher pressure from one side of the system to the other and may not be as effective as a larger pipe. I don't know for sure, I'm just thinking out loud. At 3000 cruise rpm's, there are 100 pulses per second going down each pipe, so you don't have very long to equalize them.