In 1968, a Pontiac Firebird equipped with a Ram-Air 400 V8 made a claimed 325 horsepower,
while the same exact engine in a GTO made 360.
Why? GM had a rule in the 1960s that its cars couldn’t make more than 10 horsepower for every pound of car (the only exception being the Corvette). The Firebird weighed around 3300 lb, while the GTO weighed 3600, hence the discrepancy.
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1968 Firebird vs 1968 GTO