A*b6*
I flew behind an IO-360-A1A + Hartzell (M20F), then an IO-360-A3B6D + McCauley (M20J), and now I have an IO-360-A1B6 + Hartzell (RV-7).
I personally
DID notice a pretty significant difference in feel with the counterweighted crankshaft.
FYI, the only difference between an -A3B6 and an -A1B6 is how the prop is indexed relative to the engine.
The "D" engine, i.e. the -A3B6D or -A1B6D, means it has a single-drive dual mag. As you may know, on my RV-7 I have one Slick mag and one Lightspeed Plasma II. With a dual mag, you'd be forced to go with either the dual mag or dual electronic ignition. Don't believe you can use a single mag with an accessory case set up for the dual mag (please correct me if I'm wrong).
In any case, I'm not sure what else to tell you. I'm very happy with the angle valve IO-360-A* series engines, and I'm very happy with the counterweighted "B6" crank setup, despite the higher weight & cost.
I'm also happy with my Hartzell 72" prop. Heavy, but good CG and fast. While my last Mooney did have a McCauley, I haven't flown the RV-7 with a McCauley prop, so I don't have any perspective there.
)_( Dan
RV-7 N714D (708 hours)
http://www.rvproject.com