Its not just zoomies Wayne. When you go from long under chassis headers to big tube, short runner fender exits, you get the same effect. Have to recalibrate everything and lower the idle. Seen it on every car I have ever built fender exits for. The word you are looking for though is exhaust BACKPRESSURE. That is what makes the choppy idle and correctly, zoomies have little to any exhaust backpressure.
