Even a cam that gives you only 8 or 9" vac. at idle (900 rpm's) will still operate the booster and, it should be well above that value when driving or coasting. I suggest you connect a vac. gauge and get a reading at slow idle, fast idle and maybe above 2000. Depending on final drive ratio and where you do most driving, any cam over the factory (H.P.) grind would not be my own choice. Nothing quite like getting a 'chirp' in all four gears - - and 15" vac. at idle.