I'm not sure how much interest there is, but if it's any help, I could post up some more info, carrying on from where I left off, detailing stepped primaries (I think merge collectors speak for themselves most likely) - and about the only other thing that might be of interest - since most racers now have to fit under a certain noise level, what can be done to drop the noise down, without affecting the exhaust scavenging (in short, generally any time you add mufflers, you add back pressure and as soon as that is present most of the power increase from exhaust scavenging go down the drain, there are ways to 'trick' the exhaust into behaving like it's an open pipe not too far past the collector, but it actually has mufflers further down and so the noise can be dropped under the required level. I didn't 'invent' any of this obviously, it's been worked out by people a hell of a lot smarter than me, but I do have some info I could share if anyone wants?