Humberto is right, the motors are different. And dconnor has a point, too. If the boost is high enough, the 307 will start to lose flow just when you need it, leaving more of the burden on the 340. There will still be more flow than if the 307 was on its own, and at much higher pressures, the 307 might not contribute anything. Sully runs the combo, and it works, at least up to pretty good boost levels. Of course, the 307 is still putting out 30 gallons/hr at 80 psi. How much higher will the pressure go? (The two pumps together will put out about 67 gallons/hr at that pressure! Lots of horsepower!) Of course, the pump curves are taken at the pump discharge, and don't allow for pressure drop through the fuel lines. Still, that seems to be a lot of pump.