Just made everything at least 3 decimals. I think some of the integer math was dropping the decimals for you.

select ((26.700*((504.682+14.566)/14.730)*(520.000/(460.000+64.000))*(1.00/POWER((1.00/(0.99877-(0.00000072531*504.682*64.000)+(0.00013027*504.682))),2.000)))+(19.500*((1751.84+14.566)/14.73)*(520.000/(460.000+67.000))*(1.000/POWER((1.000/(0.99877-(0.00000072531*1751.84*67.000)+(0.00013027*1751.84))),2.000))))

gives me: 4020.733146