When I bought my AMC Javelin, it had an SP2P and an Edelbrock 600 on top of the 360. The car ran a best of 15.1 to 14.9 in the quarter at Spokane Raceway. I later switched to a Performer and a Holley 600 (and ok, swapped to 3.15 gears from the 2.87) and picked up almost a full second in the quarter plus gained the ability to bark second gear. I used to have a timeslip in my wallet for my best run of 14.2 @ 99 mph, but it faded away.

(Yes, I realize that's slow. But the car was just my basic daily driver street car.)

SP2P's work better on 318's, Ford 302's, and Chevy 305/307's. Big cubic-inch engines are strangled by them. I'm not kidding! The ports are literally the diameter of a dime! When I swapped from SP2P to Performer, I was shocked at how tiny the ports were on the SP2P.