Our Engine HP ratings are very conservative. That’s why the numbers are very generalized/generic as a first impression. First and foremost the reason for these ratings is due to the fact that a dyno queen isn’t going to cut it in front of an AIRBOAT propeller. We care about the CURVE of the engine's performance in relation to the propeller's, and how it will perform in real-world applications.
    A perfect example. Our 454/500 on a dynamometer with cast iron exhaust manifolds (We were testing it for a offshore boat application) and full exhaust made 528HP at 6000RPM and 538LB/FT of TQ at 4000RPM. With Tuned headers and open exhaust made just under 600HP. But we rate it at 500HP in an airboat application.
   Let’s say we want this engine to operate at 5252RPM at maximum thrust for a prop that wants 1960RPM with a 2.68 Box. At that RPM the engine makes 510HP and 510#s of TQ. And not only is that the power that matters to YOU, but on any given day the engine will outperform it’s HP rating on anyone else’s dyno.
   Now an example on a more extreme end of an engine we dyno’d right after the 454. In this case it was a 377CID Small Block Chevy. The engine made 635HP at 7500RPM but only made 546HP at 6000. And if we put our Airboat tune-up for reliability the numbers would drop even more. Obviously not an airboat engine unless you only intended to race with a high ratio box, on a very light boat and High RPM/Low Mass propeller.
   Ask yourself this....Our 600HP engines make over 1600#s of thrust and swing a 4 Blade 82" Superwide...Do theirs?
   Below is an excellent example of a particular engine platform/displacement, with different head and camshaft choice. Hopefully this puts things in perspective, or at the very least gives you something to think about....

   This is the power curve many people preach that is required to move mass, and swing a prop. Usually has plenty of snap but you wonder why it has no real push. If you have this power curve we suggest you run a low ratio redrive, with a "soft" blade

   This is the engine that people who know how to make power in automotive applications tend to think will work in your boat. This is the engine that if it's lucky enough to break through "The Wall" of the prop will usually burn up under heavy use. If you want this power curve, we suggest you go to a light/"free" boat, a very high ratio redrive and a "soft" blade as well, that doesn't expose the engine's weak TQ curve. This curve tends to require the same prop as the "Torque Monster" just a different redrive ratio.

   This is what we build. This curve targets the use of higher ratio redrives with very aggressive props for maximum thrust. Developing a torque curve that actually makes a prop perform under airboat requirements is very difficult to achieve, and even harder to make reliable. This is why the engine combination and parts we use are over-designed to handle the stress that comes with it, and our engines of 100 less cubic inches usually outperform their competitors both in performance as well as reliability.