If you have a car that reacts quickly, then you could still use a delay box on a .4 pro-tree. But, there is no "slower" car when a pro-tree is used. Other than the Pro catagories and Alcohol catagories all other cars that use a pro-tree run on a preset index...such as Super comp, Super Gas and Super Street in NHRA and Super Rod, Quick Rod, and Hot Rod in IHRA. Of coarse Super Street and Hot Rod run on a .5 Pro tree.
TS1955