OK, that answers my question. By going with 1-7/8" OD pipe (.049 wall), it would be tuned for about 7800 rpm. Obviously, this is too high for our purposes. I'll go with 1-5/8 (.063 wall) to shoot for 6700 rpm peak power. This is typically the rpm I see on ground roll and early climb before I start adjusting the prop down to a lower rpm to transition to cruise climb.
Have you used the header designer tool available from Burns Stainless? You need to know all the timing numbers, rpm, etc. I may give it a try and see what I come up with. I have a test p-port housing that I made up to see if the tube could be welded to the inner liner. So, I can use that with a spare rotor to verify the EVO and EVC numbers.
Mark