[AstroWill]

"Back pressure" is a huge mis-conception.. and is commonly misunderstood.
It is not desirable anywhere in the system.

Most of the pulsed flow technology applies to the pipe BEFORE the muffler. Once the exhuast pulses enter and expand in the muffler..the scavenging effects mostly end. The output side is far less critical, but still needs to be adequate for volume of CFM output.

I think these really sum it up.
It seems that the header/manifold size seems to matter for scavenging, then the rest really doesn't matter as long as it flows well enough with the least amount of back-pressure.