Crazyhorse---

If set up correctly, supercharged engines have proven pretty reliable these days. I hope you retain the blowers on your engines---you need a good amount of torque to keep that size of boat moving and you'll get it from a supercharged engine. :)

Do you plan on taking one of your engines to Earhart's dyno?

They've really impressed me with the way they idle and respond to throttle inputs. It will be interesting to find out the results from the dyno runs I'm planning.

Like Turbojack said, I've not heard of many reversion problems when running positive manifold pressure.

If we could idle at positive manifold pressure, or even atmospheric balance, reversion would not be an issue.

Late exhaust valve closing opens the door to reversion, but intake vacuum is the mechanism for pulling the exhaust flow backwards. Overlap completes the chain. The piston suction has generally not developed enough to reverse the dynamic column of exhaust gas mass in the first 15 degrees or so if crank rotation we are discussing.


With that said, yes, blown motors usually idle smoother than a given cam spec would on a NA motor. It's cause you are providing a stronger pressure differential across the throttle plates and carb jets (as well as no intake reversion). A NA motor would provide a far weaker vacuum signal to the carb.

A port-injected blower motor will show a less dramatic improvement in its idling behavior, but should STILL idle better than a NA one cause there will be no intake reversion taking place which causes erratic airflow in the (usually) large runners in a port injected intake.