I found out about crankshafts the hard way as usual; if I'd a had half a brain I just would have copied current practice but no...
With my air cooled 370 engine the original crank/rod/piston brings the transfer cutouts in the piston down below the top of the liner cutouts at BDC, so that at BDC the window height is reduced by about 9mm. Does that make sense? There isn't enough meat in the piston to just raise the cutout, and anyway if you did the transfers and exhaust would short-circuit at TDC.
Still with me? Anyhow, the bottom of this window is formed by the outside diameter of the crank wheels, so I figured that by pork-chopping the crank and making the curve of the remaining crank webs slightly eccentric I could pick up that 9mm I was losing at BDC, as well as lowering the PCR a bit.
So I modified a crank, having to add some tungsten to maintain balance. Once on the dyno I found that the power had indeed changed, but not in the right direction. Torque was down at higher rpms, everywhere else there was little change.
I made two stupid mistakes, the first being a lack of research. I would have found that the effect of odd shaped cranks to cause extreme turbulence and disrupt breathing at high rpms was known of more than 50 years ago. The second mistake was to not take a close look at the current designs - if I had I would've seen smooth full wheel cranks either encased in sheetmetal shells (a la Honda) or with the holes and other iregularities filled and faired with plastic packers.
So, back to square one. The lumpy crank was obviously a dud, but I still wanted to see if a larger window had anything to offer. I ended up using a 9mm longer rod and a barrel spacer, these giving both window area and crankcase volume. I filled all the balance holes in the crank with pressed in aluminum plugs and radiused the inside corner of the crank wheels. I had to use a fair bit of tungsten to get balance with the crank mods and the longer, heavier rod.
Back to the dyno and the horsepower lost was back, plus a small increase. I know a lot of engines still use pork chop cranks and I think if rpms are moderate they are fine. But if rpms are highish (even as low as 8.5 or 9k) I really think there are measurable horsepower benefits to a streamlined crankshaft.