i just dyno'ed my 580" motor.the test headers were 2" to 2 1/8 with a 3 1/2" collector.then i tried my headers that i will use in the car.they are custom kooks 2 1/8 to 2 1/4 with a 4" collector.my bigger headers made the exact horsepower and 5-6 less ftlb of torque.it was a supprise to me......

68 cuda formula S 588" bb 5sp
70 CUDA CONVERT 500" 5SP (SUBLIME)
70 CUDA CONVERT 500" 5SP (PLUMCRAZY):TOO MUCH HORSEPOWER, IS ALMOST ENOUGH!