Greg's remarks on use of the Buick stroker crank constitutes excellent
advice on every specific. I can only add a couple of detail comments and
holistic observations. Going to an extreme stroke suggests adoption of
a different power production range than the stock use, one more compatible
with a broad torque peak (or plateau) achieved at low RPMs. Selection of
an appropriate transmission and differential combination can make such
an engine suitable for the application. Such an approach also finesses
some of the other issues by making them less critical. A generous radius
on the reduced-diameter main bearings is, I agree, very desirable. Nitriding
the crank would add strength and reduce flexion at an cost of increased
brittleness, making a generous radius more critical. The radiused area
is not a direct bearing-load surface, so it could be shot-peened after
nitride treatment to improve load bearing in shear, then lightly polished
to remove surface irregularities without removing most of the benefit of
peening. The bearing surface itself should not be shotpeened, of course,
so this is an operation requiring skill and care. Running a lower engine
RPM would limit the friction losses at the bearing surface as well as
reducing the criticality of engine breathing in limiting power; a relatively
high valve lift can be used, complemented with long induction runners, to
augment low end power without requiring large/multiple valves.
My own inclination would be to resist stepping up to a larger bore, and to
instead optimize the engine to generate buckets of power from low RPM and
throughout a modest RPM range. This approach would probably keep the engine
operating within its structural limits, though certainly I know that more
RPM equals more power...
Greg correctly focusses on the problems of crankshaft torsional loading,
and all I can suggest there is to pay attention to crankshaft balance, and
in particular to make sure that the crankshaft weights in primary opposition
at webs 1 & 8 are as proportionally balanced as possible, with balance
concerns diminishing as one moves toward the center web. And, of course,
put the best available harmonic vibration damper on the engine, even if
it calls for a reduction in flywheel mass to compensate.
-lar
"Nay, even the sins of lying and perjury are nowhere punishable by laws; unless
in certain cases, in which the real turpitude of the thing and the offense
against God are not considered, but only the injury done unto men's neighbours
and to the commonwealth." - John Locke, A Letter Concerning Toleration (1689)
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