Cheers, not sure how a setup like this would compare to a 4 into 1 with the same length primaries etc, I guess there would be less resistance to flow due to less bends, although would there be turbulence at the collecter and I am also guessing that if there was a scavenging effect in a 4 > 1 system then the effect would be weaker as it would draw on all pipes at once in comparison to only one at a time for a 4 > 2 > 1 ??

also another thing to think about is the initial angle of the exhaust coming out of the exhaust manifold. I have notice in both of the extractors that I have for A series, the inner 2 exh. pipes turn sharply straight at the manifold.

qik1000, if you do decide to get them custom made, see how much clearance you have to play with (also check if you plan on changing carbs, manifolds etc later on, check those clearances too) and steer towards making them as straight as possible when they come out of the head, or atleast a smoother bend then the headers I have seen so far...

Hope the ideas help mate.