i eventually plan on building up a pretty mean street car..but at the moment i'm poking around hearing many opinions and forming my own..my question is..how would a lightweight crank fair power-wise as opposed to a lighter than stock crank..for instance i know scat makes a crank in a 3.48 stroke that weighs 42lbs(i believe) and then you'll also find that they(scat) make a crank with a 3.48 stroke that weighs roughly 75lbs(i believe)..would the crank that weighs more translate into more power because of more centrifigual inertia or would the same power be made given all other aspects of the motor were the same (compression ratio,combustion chamber size, valve size, cam size)...i guess basically what i'm asking is would a lighter rotating assembly make more power or the same as a heavier rotating assembly just at a higher rpm..thanks for you time and input in advance..
lucas

 

Just the opposite:

Lightweight rotating parts require less hp to accelerate, which is what we're doing most of the time when our foot is in it, so more hp is available at the flywheel. At a steady engine speed, rotating weight (inertia) doesn't matter.

The 42 lb. crank will show some gains in a 300 rpm per second acceleration dyno run, and more gains at 600 rpm per second over a 55 lb crank. I don't think any 75 lb SBC cranks are available. If so, they'd be useful only for something like a stationary generator engine.

Unless you need the strength (42 lb Scat cranks don't come in anything but "strong"), are revving quickly, and plan to use other lightweight parts inside the engine, the extra $ for the superlight probably are a waste. Spend your money on cubes and heads.

My $.02

 

Wouldnt there be a slight advantage out of the hole when droping the clutch because there is more inertia?

Another point is, not only is accelerating increased with the lighter crank but deceleration when shifting. Also the lighter crank will cause less windage because they have shaped counterweigts and slice through the oil instead of slaping it like most cranks with square counterweights.

 

cool thanks for the input..i was thinking that the lighter-weight crank would be the more efficient because it would take less power to rotate and it would rev faster..i guess really in the end it comes down to what can the pocketboot handle..i eventually plan to run a all motor setup probably consisting of like a LT4 top end and i was thinking possibly while having that done just kinda cleaning up the motor maybe having the cylinders cleaned up and the journals cleaned as well..but who knows when i'll get around to that..for right now its paying off my current bills before creating others..thanks again for all of your input(s)
lucas