Well, I've finally taken delivery of my Z3 racer. It's got a set of 6-into-2 headers, but there's no exhaust after the two collector pipes. My plan is to fab a two into one pipe and route that back to the rear sub frame and end the exhaust there with a clamp and a down turn/muffler depending on track noise requirements. So what I'm wondering is how long should the two go before they merge and also how big should the merged pipe be. This is on a 2.8l with the power band of 3500-7000 rpm. Thanks,

James