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Lately in the drag racing scene here in Australia, we have seen a bit of a trend towards cam driven mechanical pumps, with PRP producing billet brackets to mount the USA made Kinsler branded pumps.
My question is, how different are these to tune for? Since the flow is directly proportional to the camshaft RPM, the potential flow rates, and hence the available fuel pressure would vary quite a bit throughout RPM.
How is this compensated for? Do these systems simply use a traditional fuel pressure regulator to cap the maximum pressure, and you simply increase the duty cycle at low RPM to compensate for the pumps lower flow rate?
I'm keen to learn how these work!
The actual fuel pressure that the engine sees is no different. While the fuel flow is obviously linked to engine speed, you still use a regulator to control fuel pressure. You do need to be a little careful though due to the fuel flow at high rpm which can overcome the return capability of some regulators. There are specific regulators available that are designed for mechanical pumps such as this - https://www.aeromotiveinc.com/product/belt-drive-pump-efi-regulator/
OK, so since the pressure is held at a constant then there's essentially no difference in tuning and electric vs mechanical pump.
Keep in mind that we are talking about cam driven mechanical pumps for return-style port injection. Direct injection uses cam driven pumps and dynamically change fuel pressure and injection pulsewidth. So make sure you keep that in mind for any future projects.