I think what is going on here is when someone puts a part on a car and sees that the manufacturer says that it will give the cara 5 hp increase. So that is addes to the total power of the car. Like this pullies = 15 hp, fullexhaust = 25 hp, cold air = 10. 10 + 15 + 25 = 50 so now the car is at 275 hp.
http://reality.sgi.com/staheri_corp/mycar/bop.html is a good test on common parts for the 302.
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90 GT 150k on the motor never had the valve covers off, 1 5/8" headers, x-pipe, 2chamber flowmaster,fms aluminum ds, 3.55, best time on 245/45/17 2.08 60', 13.906 @ 98.98