Using an on-line 1/4 mile calculator, the 45 hp. increase between the 6.1 and 6.4 will be .4 sec. (estimated) in the quarter mile. That is 4 car lengths!

Here are the projected times, per the calculator, based on a weight of 4,150 lbs:

6.1 (425 hp.- flywheel)= 13.12 sec.
6.4 (470 hp.- flywheel)= 12.68 sec.

http://robrobinette.com/et.htm