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Burns, According to what we learned years ago from drag racing is that lower rpms need long runners and high rpms need short runners. This is all based on the fact that a column of moving air has momentum. When the intake valve closes the moving air stops at the valve but father up the column the air continues to move and push against the air immediately behind the valve. This "stacking" of air leads to an increase in pressure at the valve. When the valve opens the air enters the cylinder uner pressure rather than a vacuume. That, in turn, puts more fuel/air mixture into the cylinder during the intake stroke. The long column of moving air will continue to enter the cylinder even as the piston rises as it begins the compression stroke until the valve is finally closed. The trick here is to balance the length of the runners with the rpm. This "super charging" effect works very well at 1 and only 1 rpm. Any other speed and the pressure pulse and the valve timing will be off a little. Mopar used the twin four barrel carbs on the cross ram intake to good effect years ago. It was availible in two different runner lengths depending on what your anticipated application was. They worked very well in a narrow rpm range, either high or low, depending on the runner length, but outside of that range they didn't function any better than a good cast aluminum intake. If you know the rpm at which you entend to run you JD, you could "do the math" and determine what runner length (and diameter) would function best. As far as "swirling" you don't want turbulence in an intake manifold. You want clean, straight movement of the air column. Turbulence is only needed in the combustion chamber. That is why most high compression engines use a "squish area" between the head and the piston top. This set up squishes the air toward the spark plug and is supposed to induce a swirling effect to better facilitate combustion. Try it and let us know how it goes. Jerry
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