performer rpm vs airgap horsepower

The latest hot Rod issue (November 2011) has it again...

About a 4HP increase at 6,200RPM and overall an average 2.1HP over the whole power range (2,600 to 6,400)...verses the Performer RPM.

One thing they did say was...maybe the results under a hood in a hot engine compartment would be different (verses the dyno room with good air flow).

Paul