When Paul Yaw was on Paul L's list we had this same discussion but for a PP engine.  He recommended starting with a 1.5" dia throttle body for each PP and stated that it should produce between 200 and 215 HP.  He is obviously a proponent of high velocity in the intake tract.

Ken Powell

Thanks Ken, that's re-assuring.  My TB is 1.57" diameter for each rotor, so I should be OK.  

 

Rusty