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When calculating fuel pump requirements for larger injectors what is a good margin to have of pump flow vs Inj flow.
6 X 42lb/hr injectors can flow 252 lb/hr.
1 X Bosch 044 can supply - 445 lb/hr @ 55 PSI
This pump will obviously be well and truly enough for these injectors. Is there a margin that is ideal to factor into a return fuel system to ensure adequate flow rate through the rail?
While I wouldn't call it a hard and fast rule, I try and maintain an excess flow potential of around 25%. This isn't essential and provided your pump can outflow the injectors at 100% duty cycle then you should be able to maintain pressure, however it's recommended to have some level of excess to ensure you maintain pressure, and also when installed in the car you'll often find the pump flow drops from the manufacturer's stated flow figures due to voltage supply and/or flow restrictions presented by the lines.
Bringing this thread back from the archives:
My build consists of 4 x 1,350cc/min injectors for a 2.0 turbocharged engine that will run on both gasoline and E85. My goals are for 625hp and the crankshaft (about 525 at the wheels). I will be running a base pressure of 55 psi. My injectors are 1300cc/min at a base pressure of 43.5. I'll be boosting up to 20psi. The pump that I currently have is an Aeromotive Stealth 340lph. It will be wired with the appropriate gauge wiring and relay to ensure a good supply of current from the electrical system.
Should I consider a larger pump? Will this pump have sufficient headroom to fulfill my goals?
In a perfect world, the Aeromotive Stealth 340lph will support your fuel requirements on pump gas but you might run into problems with E85 (https://www.aeromotiveinc.com/tech-help/faqs/faq-340-stealth-fuel-pumps/).
A quick back of an envelope calculation suggests it may be marginal for max'd out injectors at "base+100% reference" pressure as there will be a proportionately increased fuel flow and reduced fuel supply* due to the higher than spec' pressures. E85 would make that worse, as would anything that affects the theoretical flow.
However, as you are unlikely to reach that point you should be fine, but there may not be much margin left in reserve. Is there a flow Vs pressure Vs applied voltage graph available - I didn't see one on their site*?
Ah, did find one - at a nominal 13.5V, flow will drop to ~250l/hr at 75PSI (base plus 100% reference boost) with a current draw of just under 12A.
Thanks guys. I'll opt for the E85 Walbro 450 then. Anyone want a lightly used Aeromotive Stealth 340 for cheap?