I see no problem with the air mass calculation.

For VE I use a value in the range of 0.87 to 0.95. The lower is for a stock 930 cam with a muffler. The higher is an all-out effort with no muffler.

For BSFC I use this curve:

For 500 HP @ 5000 RPM I get (372.9 x 365)/1000 = 136.1 kg/hr of fuel, or 2.268 kg/min

For a target A/F of 11 that is 11 x 2.268 = 24.95 kg/min air or 55 lb/min, which is about what you were getting with your unofficial squirrel calculator. The pressure ratio is what is jacked.