As stated above, 1hp/10lb was the GM mandate. When the top brass first saw the 3400 lb 67 Firebird 400, they knew it had the GTO engine, and the engineers tried to underrate the Firebird 400....on paper.
The engineers attempted to convince the top brass that the Firebird engine was detuned, but the top brass knew DeLorean (and Pontiac) all too well. To appease GM, the engineers came up with a cheap way to limit the throttle opening on the Q-jet, and that made GM happy.
In every original road test where a Firebird and GTO squared off, the Firebird was always 2/10's quicker. Of course, the road testers already fixed the Firebird carb to allow full throttle.
By the way, not only were the engines the same between the GTO and Firebird, and the Firebird weighed less, but the RAIII/RAIV Firebird exhaust manifolds outflowed the GTO RAIII/RAIV versions by about 5 hp.
