I see 2 issues right off the bat with these manifold. The first is the flange thickness (which someone already mentioned). I think there would be too much stress on that thin of metal. My Magnus is at least 1/2" thick.
The second problem is the runners. A good design will have tapered runners and velocity stacks. Tapered runners will increase velocity due to the pumping action of the incoming air flow. When i used to port out 2 stroke engines, you always wanted to make sure the intake tranfer ports were larger at the base(crankcase) than at the window in the cylinder to avoid a reverse pumping action.
Here is a link for everyone to enjoy:
http://www.turbonation.com/intake.htm
While these ones on ebay may improve performance, they certainly could be improved.
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