I'm not saying there is only 28 hp of loss, you are.
I'm saying that 30 lb injectors are good for ~385hp. You can spin it anyway you want. A certain amount of gasoline can only make a certain BTU which can only make a certain HP. That is fact.
Here's some valid numbers...
Injector size (lb/hr) = (horsepower x BSFC)/(no.of cylinders x duty cycle)
30 (lb/hr) = (385 x .5)/(8 x 80%)
Even if you up the duty cycle to 85% it's still only 400 hp....
Either the formula is wrong or the dyno. You decide, since according to you, there is no way in hell he can only have 28 hp in loss....