The SCAT crank that I used costs about $2500 so it isn't cheap but 440Source sells a low buck lightweight crank. Theirs isn't nearly as light, but it sells for $900.
Holy crap that's a lot of money for a SCAT crank! Every SCAT product I've ever messed w/ was WAYYY cheaper than that. The Callies magnum crank that's in my hemi was $1800.
It'd be nice if it was easy to do a back to back test and see just what a lightweight crank is worth as far as power and/or ET at the track. Obviously that isn't feasible, but I bet the power per dollar is pretty low. I built some sb chevy roundy round motors w/ SCAT Ultralight rotating assemblies. While they were pretty light and impressive looking when on the engine stand, I don't think it was necessarily worth the money.
