Thanks for the info Tom!!

I found the old saved files from the older GM Powertrain information I had saved on these engines. Including these GM Marine power charts. The 375 HP engine used the factory truck cam and achieved its power with a freer flowing intake and exhaust and a different rating system. The 425 hp used a hotter cam and in some years a forged crank. The forged crank was later dropped. The factory light duty truck/van/SUV engines are 340 HP and 455 TQ. What that tells me is with the intake/shorty headers, exhaust and tuning this 8.1 should be getting close to the 400 Net HP and 475 Net TQ range. That is approaching direct injected 11:1 compression 6.2 HP levels without reving as high, without a cam phaser or direct injection.

375 HP


420 HP (Mercruiser 425 HP) I love how the TQ curve starts over 400 ft/lbs down near 1,000 rpm and it hangs over 400 ft/lbs even up at the 5,200 rpm redline. Downshifting into 2nd accelerating to pass should be a breeze compared to the stock truck cam.