Gene,
The bore spacing doesn't limit power output, per se. It DOES limit cubic inch potential, which in turn, CAN limit power. At the 500 CID range, there's no big advantage to the BBC with the 4.250" bore. It still needs a 4.25" stroke to get it there. Now, a 4.500" bore with the 4" stroke is a different matter. That's how "502" gets there. But a 505 Pontiac (IA-II based, 4.25" stroke) will make more torque than a 502 at the same level of tune. The 502 will certainly make more high-end horsepower, if the Pontiac is somewhat conventional in nature.
But comparing the Chevy to the Pontiac is apples-to-donuts. One is a great low-end/mid-range power plant (street applications is where it really shines). The other is a great high-revving power plant. And applying all the "goodies" available for the BBC today, is not a fair comparison, either, as there was a 20 year interruption in the developement of the Pontiac. Stick around a couple more years, to see what Tiger heads will do for the Pontiac. None are out there in max-developed form yet, unlike Big Chief. Forget the old rectangular port heads. Pontiacs have moved beyond that level of power, even with just Edelbrocks.
NOTE: Our shop doesn't care what color you paint an engine, we'll build it. We have mass experience with both BBC and Pontiac.
LSx engines do use at least two part numbers from the old small block Chevy. The lifter (factory hydraulic roller) and rod bearing. There are other engines from GM Powertrain Div. that use those same parts, though. That said, there is no design relationship between the old small block and LSx. LSx is actually much more like a Ford than it is like a Chevy. And the heads? Artwork, man! All in all, LSx is a great design, especially in the "modern world" of OHC and multi-valve heads. GM's "in your face" pushrod engine! Of course, this is just my opinion... I could be wrong!
Jim
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