I notice several custom headers on the market. Some have cylinder 1 & 2 merging into a y-junction and 3 & 4 in a y-joint, then they merge into a y-joint and then into a collector. I also seen this on Yoshimura exhaust for motorcycles. The most common combo are 1 & 3, and 2 & 4 tri-y. What are the advantage(s) of combining 1 & 2, 3 & 4 tri-y over the typical 1 & 3, 2 & 4 set up? Of course this is probably depended on the engine size and modifications, but just want a base understanding of difference. Would the 1-2, 3-4 combo produce more top end or mid range torque?

 

Anyone?

 

wait for one of the header guru's like smsp or rmf to chime in