As this engine has the intake and exhaust manifolds in one flange I have to build the Intake and exhaust at the same time. Using Solidworks I sketched up the flanges and got them laser cut out of 10mm mild steel. Shopping around I found that Stainless Design was pretty good on price and and had good service (also have a work account with them).
I started looking around for Extractor calculations to get the right size pipe diameters and primary lengths. I found it hard to find a reliable formula as some of the sizes seemed too small or too long. In the end after talking to a few people I just went with best guess. My first design was 4-1 style extractors but after reading a few forms and doing some research I settled on a 4-2-1 design. Lucky there is quite a bit of room in my engine bay.
In the end the Intake is 38mm, Exhaust is 32mm Diameter for the first 315mm then 40mm after the join with a total length of 1100mm finishing with a 50mm section