Pontiac Firebird 400
In 1968, Pontiac introduced the new Firebird with a 400 V8 engine with 320 HP. Immediately after the introduction, car fans publicly asked the factory why the new 400 V8 engine in the Firebird is rated at 320 HP. In comparison, the same 400 V8 engine in the GTO made 366 HP (via Hemmings).
Pontiac didn’t reply, and soon, the answer came from the insiders from 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. Despite the underrating, the new Firebird 400 was very fast, especially if equipped with an optional Ram Air induction system.