I swear they start out with factory HP ratings and build from there. I assembled a stock spec 273 and it came out to within a few horses of the oem 235 horse claim. After modifications, who knows. It seems pretty generous.
I just punched in a known combo from IQ52 with all his detailed information, down to head flow at H20 at test. They came in 3 percent lower across the board. But yeah I punched in stock 1968 440 hp and specs, they came in at 379hp vs the factory rated 375.
