I would agree that the MP cam would make 11" of vacuum on a 340, wouldn't you agree that OP's combination is not sorted out and when the timing and fuel delivery is tuned properly it should make about 14" vacuum at idle?
I don't care how much of a magician you might be, a well tuned engine with a longer duration cam and tighter lobe separation is going to have less vacuum and worse street manners than The same well tuned engine with the only change being a shorter duration cam and wider lobe separation. They both contribute to overlap which is a major factor in street manners and idle vacuum. The cam OP runs is 11 deg overlap @ .050 while the cam you're suggesting is 29 deg @ 0.050". How can you honestly think this won't have an effect?
