Using speed it's down 31hp, ET it's down 51hp. I'm not sure how much loss there is driving the water pump, fan and alternator, plus header and ignition differences.
And that makes perfect sense. You add in those variables and the dyno is pretty damn accurate.
Plus, the fact that you tune your stuff makes HUGE difference. Out here, in the NW, most guys don’t even know HOW to tune. So they just drive the stuff and it runs what it runs.