I'm preparing to have twice pipes installed in my 72 "refreshed" car. I'm using an L28 with SU's into a 6 into 2 header with the intent of running dual pipes to the rear. Do I need to have a cross over tube behind the collector to equalize the exhaust pressure. The old set did not have this but came of the stock manifold. The local "know-it-alls" are pretty evenly split on whether it should be done or not. Any of you guys running them using a cross over tube? I know years ago when I was a gopher at the muffler shop, we did it on the V8's when we did dual exhaust systems. Don't ever recall splitting a 6 cylinder unit.

As a side bar, the original (at least the pipes that came on the car) were 1 1/4, I am planning to use 1 1/2. Any thoughts there? It is only dumping 3 cylinders...

You will not need a cross over pipe on a L6, look at the firing order, on my twice pipe i run 1 3/4 inch, that equals to 2.5 inch single pipe in opening.

Chris

Twice pipes are a style/sound thing and adding a crossover will change the sound.

As I understand it, a crossover pipe is only necessary if ther are separate cylinder banks, I don't think it makes mutch of a difference with an inline engine.

As I said, twice pipes are a style/sound thing. From a performance standpoint they are not as good as a well deisgned single exhaust. Same is true for most V engine installs. A well designed single exhaust will develop more power and torque then a dual exhaust because you have more waves to tune with. Unfortunately, packaging considerations with a V engine make a well designed single exhaust extremely difficult and generally not worth the labor costs vs. the power improvements.