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 1 horsepower for every 10 pounds of car (the only common exception being the Corvette, the other secret exception were 427 SS Chevelles sold on Indian reservations). The Firebird weighed around 3300 lb, while the GTO weighed 3600, hence the discrepancy.