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Thread: Return vs Returnless Fuel System

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    Default Return vs Returnless Fuel System

    I'm planning a Sniper EFI install for my '69 Nova. I need to decide to go with either a return style fuel system (PN 19-165) which requires a new tank (costs more) or a returnless retrofit system (PN 12-300). With a return style system, fuel pressure will always be regulated to a consistent pressure at the fuel rail. With the returnless style, the fuel pressure is regulated at the pump in the tank, so when there is high fuel flow, pressure drop through the line will go up, reducing the pressure at the fuel rail, and thus the flow rate through the injectors, causing a lean condition. My understanding from emailing Holley tech and Chris at is that with a returnless system the Sniper ECU relies on the WBO2 sensor to sense a lean condition and then increases the injector pulse width to compensate.

    To make matters worse, at low load and fuel flow, such as at idle, the engine will be under vacuum. So if the fuel rail is at 60psig (74.5 psia) and the intake manifold is at 7.3 psia (15 in Hg), the delta pressure across the injector, which is what determines flowrate, is about 67.2 psi. When the engine goes WOT, fuel flow goes up, increasing pressure drop, the manifold pressure also increases. If we get 14.5 psia manifold pressure, and let's say 3 psi of pressure drop, we are at 71.5 psia at the fuel rail, for a delta pressure of 57 psi across the injectors.

    My question is has anyone run the returnless style fuel system with the Sniper EFI? Any poor running or lean out at high load, such as flooring the throttle from idle? Anyone have experience running both of these fuel systems that can compare the performance? I know the OEMs use a returnless style, but in that case the pumps are usually pulse width modulated to increase pump speed as fuel demand goes up, which is not the case with the Holley retrofit system.
    Last edited by NovaDude; 08-02-2018 at 03:38 PM.

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