Hello Pete; The intake needed is correct at about 8 inches. Intake and bypass design is complicated and not as simple as it may seem. You need to figure out mass flow of the engine, air temp, tailpipe velocity, intake size, bypass ratios and many other things. A good design can loose as little as .5 lbs and a bad design can loose you as much as 25%. My best advice to you is to look at the BVM Bandit design as a good foundation. Bob has spent a great deal of time and money with an engineer to figure these things out.