Hi there, hope someone is able to help me. I am trying to find some info on early intake manifold designs, for Ford 4 cylinder engines, otherwise known as the T-, A- and B- engines. These engines came standard with two intake manifold inlets, and 4 exhaust manifold outlets cast into the block. I have found lots of pictures of after-market dual-carburettor manifolds. These used dual intake runners, with two general systems. In the first system, the carburettors mounted on a common plenum, which then opened into the intake runners. In the second system, the carburettors were mounted at the top of the intake runner, with a cross-over pipe linking the intake runners. Does anyone know the theory behind this cross-over pipe, or seeming balancing of the intake runners? Is one more effective than the other? Can anyone point me to a source that might explain the principles? Cheers Bret W.