Well, initially, the 7.3l was like 200-250hp and Ford's first attempt at turbo engine in the pickups. In the last 22 years, Ford has made numerous changes from the 7.3 to the 6.7 to where the 6.7 now has output over 400hp and torque exceeding 800fl/lp. The 6.7 was a Ford design, not an adaptation of another company's engine as was the 7.3 Within the constraints of the EPA, appears Ford has done a damn fine job of building a diesel Super Duty that doesn't need the upgrades the 7.3 loved.
Could some parts be made differently and increase the numbers? Sure, but Ford didn't build just one or 100 trucks like an individual buyer but designed the trucks for 100,000's and for the last 7 years. For the average owner, 400 plus hp and over 800 ft/lb of torque is more than enough.
With the electronics and EPA, you can create more havoc improving the 6.7 than you want to deal with trying to solve them. Does an increase of 50 or 100 hp and similar torque values justify the cost and lose of warranty coverage? Do you need this increase to make a run to the local grocery store? Probably not, but to some, they want the "old school" mods thinking it looks good and makes them king of the hill. Can you make the truck better than Ford, sometimes but rarely does it happen.
Just my $.02. I had rather spend money on other goodies than re-engineering something that is pretty damn good from the factory.
