Engine dyno software. Anything good on the Internet?

It's no oversite. It's the way the system applies limited and generalized info to it's calculations. Think about simple math: 10.346 + 5.987 + 25.976 + 3.500 is 45.809. Now let's "generalize" those numbers a little so it's 10.346 + 6 + 26 + 4 = 46.346. Simple rounding of four simple math operations and we got 1% error.
Now do that for flow characteristics of ports, and intake combinations, and carburetor efficiency, and exhaust port and header design - and apply those to every calculation that goes into calcuating torque and horsepower along a series of RPM from 2K to 6500. It will still plot trends, and sometimes it gets pretty close to dyno cell reality but it's not gospel. And dyno cell reality isn't reality.