the variables are different. from the two examples you gave.
here taken off afr site. 30 hp differece from same motors. are now gonna say afr heads are junk too?
480 HP
383ci
AFR Street 180 Aluminum Cylinder Heads
9.5
Holley 0-4779 750 cfm
MSD Distributor 36° Timing
Comp Cams 12-432-8 Hyd Roller Cam
1 3/4 Headers
93 Octane Pump Gas
Engine built and dyno tested by America
450 HP
355ci
AFR Street 180 Cylinder Heads
9.5
Holley 0-4779 750 cfm
MSD Distributor 36° Timing
Comp Cams 12-432-8 Hyd Roller
1 5/8" Headers
93 Octane Pump Gas
Engine built and dyno tested by AF