[Formulajones]

Originally Posted by Dragncar

The 390 HP 428 was the highest rated factory HP of any Pontiac in the muscle car era. The 1970 D port 64 head 455 was rated at 370 HP. The RA IVs were close to that also.
They are all under rated. But its still sad that 390 HO 48 headed 428 with dished pistons never made it into a GTO or Firebird. And they all had cast rods, just sad. And we never got a 455 with real compression and real cam either.
Pontiac always had one hand tied behind their back.

It really wasn't just Pontiac, but all of them dealt with the same cubic inch limit up through 1969. It wasn't until 1970 when that was lifted so by then with other manufactures going to 450+ cubes it only made sense Pontiac would do the same. I mean lets face it, with the cubic inch limit lifted it killed the playing field for the 428, or anything smaller than 450 cubes for that matter if you wanted to keep up.

Besides, 242177P answered Steve's question at the very beginning of this thread about the HP wars and the reasoning behind the ratings. It was all weight related.
And as you said, pretty much all those HP ratings are under the mark anyway and in most cases doesn't represent what the engines really made from any of the manufactures, not just Pontiac. It's kind of a dead topic that's been hashed out for decades since.