A couple of years ago, I saw a manifold test in a magazine (Car Craft, I think) in which they tested several manifolds on a dyno mule (360, moderate hop-up) and the manifold that made the most horsepower was an M-1 single-plane, but it only beat the Eddy Air Gap by ONE horsepower, and gave away a bunch of mid-range torque in the bargain. Not a very good deal..
