[alberg30] Re: AT4 and props

[Gordon E. White]

From: "Gordon E. White" <gewhite at crosslink.net>

      I am no expert on marine engines vs prop pitch, but I do know a
thing about internal combustion gasoline engines. It is probably not
going to hurt the Atomic Four to turn at its rated cruise RPM - just
below its max torque on the power curve. It actually puts more strain on
the crank and bearings to lug it well below its rated RPM than to run it
a little faster. Diesels are sometimes designed to turn lower RPMs than
gas engines and they have stouter crankshafts and different bearing
design.
    I don't mean to suggest twisting the Atomic Four to 5,000 RPM, but
unless it has significantly bad oil pressure or other problems that
you'd want to take care of, I doubt you are going to do damage to it at,
say, 2,400 or more. (most high RPM troubles come first in the valve
gear, but the Atomic Four is not going to get anywhere near high-speed
valve float.)
    Low RPM running puts more strain on the crank than high. Model T
Fords used to regularly break crankshafts if lugged at low RPM. I have
done damage to my race engine by running it at too low RPM and stepping
on the gas. Something analogous is going to go on in the A-4 if lugged
at too low speed. Remember what happened when you started to drive and
got into high gear (stick shift) at too low a speed? It bucked. Bad for
engines and drive lines.

                                    - Gordon White A-275


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