Center counterweights on a crank

[flapjack]

I've noticed that some cranks come with center counterweights and others don't. I want to say nitro burners have them but pro stock and top alcohol don't. What is the deal with that?

 

[flapjack]

I've noticed that some cranks come with center counterweights and others don't. I want to say nitro burners have them but pro stock and top alcohol don't. What is the deal with that?

I'm guessing it's for less reciprocating mass on the higher revving engines. That and better balance in the extreme torque fuel burners.

 

[flapjack]

Someone filled me in on this. Has to do with different balance needs for a TF engine. This makes the crank heavier and as such crank life shortens. Lighter reciprocating mass means one doesn't need the full eight counterweights.