I agree in part with RADAR at least in the tract that he is on. If we start with the 3K Rpm he suggests (you can pick what ever Rpm you want your scavenging to go to work) that means there will occur 1500 exhaust events divided by 6 cylinder for 250 exhausts per minute or 4.17 exhausts per second. This means each cylinder will generate an exhaust pulse every 1/4 second approximately. Because of the firing order (1 5 3 6 2 4)and the 720 degrees that is required to complete a full cycle of any individual cylinder we now have 240 degrees or 1/2 second between exhaust pulses in siamesed ports. Stepping back to the firing order we see we still have an exhaust pulse into the header every 1/4 sec so we become aware that optimum merging of the sequential pulses becomes more important than the size of the siamesed port. Because this post has gotten a bit extended I'll wrap it up by saying that making all primary tubes the same size will optimize the scavenging characteristics. The size and length will control thr Rpm range that the scavenging takes effect. Best Regards.
