I think a single plane is ideal but in the end its not super important I don't think. A friend of mine is just getting the bugs worked out of his home built 85 mustang with a HX40 turbo. Its a stock 92 302(freshened) with a small cam, a dual plane intake, holley carb, and HX40 turbo running 6psi. The dual plane doesn't seem to be holding it back any as its making some steam.