[25stevem]

The advantage of running higher ratio rockers are greater lift and about 4 degrees more duration over the nose of the cam lobe.

A motor with a longer / bigger stroke then it’s bore size gets starved for air faster as the rpm’s go up then a motor who’s bore is bigger then it’s stroke, even when where taking about lightly reworked iron heads.

With a motor like above its best in terms of max power ( both torque and Hp ) to run valve lift greater then where peak air flow takes place into and out of the heads.

Most post 1967 stock iron d ports attain peak flow at .550” lift.

If you run a cam of .500” lift rates with 1.5 rockers and replace them with 1.65 rockers you will then have .549” lift.

Getting back to added 4 degrees of over the nose duration produced from going to 1.65 rockers, the great thing about that is this added duration does not really have much effect on the idle quality of the motor, nor degrade low speed torque.

The only question left then with a 4.210” stroke motor is weather or not to run 1.65 rockers on the exh side also since this can help or hurt power.

In general if your running iron heads With 1.66” exh valves with no decent level of porting work and you have added 1.65s to the intake side then you should also run the 1.65 rockers on the exh side of the motor also.

Many times even if your heads have 1.77” exh valves there are so many other interrelated factors taking place ( cam, headers or not, compression, running open headers or not, that the only way to nail down what the motor responds to in a positive way is by empirical testing, as in doing a A vs B test.