Pontiac Firebird 400
When the Firebird debuted, it caused quite a stir among performance-loving car buyers in America. It was a pretty coupe with a wide arrange of optional extras and one of the biggest engines you could get in a pony car – Pontiac’s 400 CID V8. Back in the late ’60s, GM had a rule forbidding manufacturers to produce vehicles with more than 1 hp for every 10 pounds of the car’s weight. This rule aimed at stopping manufacturers from making insanely overpowered models, and all GM’s products and brands had to follow this. The only exception was the Corvette (via Hagerty).
In 1968, Pontiac introduced the new Firebird with a 400 V8 engine, which was rated at 320 HP. Immediately after its introduction, car fans publicly asked the factory why the new 400 V8 engine in the Firebird is rated at 320 HP while the same 400 V8 engine in the GTO makes 366 HP. Pontiac didn’t reply, and soon the answer came from insiders at the factory. The new Firebird 400 weighed 3300 pounds. So, to make it eligible under the GM 1 HP per 10 pounds rule, Pontiac had to rate the 400 V8 engine at 320 HP.