I think the collector effect begins to change as the nitrous goes up, somewhere around 200/250 shot, nitrous being alot like a blower or nitro, introducing it's own oxygen into the cylinders. You'll notice that the true 10.5 big inche 3 stage nitrous motors still run collector headers but they are short primaries, like 24" long into collectors, gaining on the bottm end but not losing it on the top end. also the A fuelers run zoomies but they are running nitro which also introduces oxygen into the cylinders.
Just a guess because i don't run nitrous or nitro
Zip.