044 Fuel Pump Flow Rates, Mercury 2.5 Liters
- Mike Hill
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- Apr 6, 2025
- 4 min read
Updated: Aug 5
044 Style EFI Pump Flow Estimates at Varying Voltage & Pressures
The Buckshot Racing #77 high-flow EFI fuel pump is an external inline, Bosch 044-style pump developed for demanding marine EFI and motorsport fuel systems. The term 044-style describes the pump’s high-flow external configuration and installation category; this is a Buckshot Racing #77 pump and is not represented as a Bosch-manufactured 0 580 254 044.
This pump is intended for properly designed return-style EFI systems where dependable fuel volume must be maintained as pressure and engine demand increase. It is well suited to custom and high-performance Mercury installations using large fuel lines, an external regulator and an electrical system capable of supplying stable voltage under load.
Published Fuel-Pump Flow Ratings
The Buckshot Racing #77 EFI pump is rated at 79 GPH, or 300 LPH, at 43 PSI and 13.5 volts. At the same 43 PSI pressure with voltage reduced to 12 volts, output is rated at 67 GPH, or 255 LPH. At the considerably higher pressure of 75 PSI and 12 volts, the pump is rated at 53 GPH, or 200 LPH.
These ratings demonstrate two important characteristics of an electric EFI pump: output changes with both fuel pressure and voltage. Pump flow does not decrease by a fixed percentage for every 10 PSI increase, so a generic pressure-loss formula should not be used. Final pump selection must be based on an actual pressure-and-voltage flow rating that matches the engine’s operating system.
A simple interpolation between the supplied 12- and 13.5-volt ratings would place output at approximately 276 LPH at 12.7 volts and 43 PSI. However, that figure should be treated only as an estimate because electric-pump response is not perfectly linear and installed flow is affected by wiring resistance, filters, fittings, hose length, fuel temperature and inlet restrictions.
Pump Voltage Must Be Measured Under Load
Resting battery voltage is not the correct value for evaluating fuel-pump performance. What matters is the voltage measured directly across the pump terminals while the pump is operating and the engine is under load. Voltage can be lost through undersized wiring, long cable runs, weak relays, corroded terminals, poor grounds and overloaded electrical circuits.
For comparison, Bosch specifies a 13-volt operating point for its current FP 200-7 high-performance external pump and lists current demand as high as 17 amps at 5 bar. This illustrates why a high-flow pump requires a dedicated fused relay, correctly sized marine wire and a clean, short ground path.
Mercury 2.4L and 2.5L EFI Applications
The Buckshot Racing #77 044-style fuel pump can be used in properly configured external-pump systems for many Mercury Marine and Mercury Racing 2.4L and 2.5L V6 EFI engines. Common applications include the Mercury 2.4L Bridgeport EFI, front-injected Laser EFI and XRi engines, 2.5L EFI Offshore, 260 EFI, 280 ROS, 300 Drag and S3000 race engines.
Mercury used different fuel-system arrangements and regulated pressures across these engine families. Mercury technical information identifies approximately 36–39 PSI for systems using an external electric pump and approximately 34–36 PSI for certain engine-mounted internal-pump systems.
Mercury Racing engines may also use higher-pressure race calibrations, including 56 PSI systems, depending on the ECU, regulator, injectors and original engine configuration.
For that reason, the engine’s required pressure must be confirmed before installation. A pump should never be selected only by engine name or horsepower. The regulator pressure, ECU fuel curve, injector calibration and return-system design must all match.
The pump’s published 200 LPH output at 75 PSI and 12 volts shows that it retains substantial flow at pressures above the common 39- and 56-PSI Mercury EFI operating ranges.
This makes it suitable for many stock, modified and naturally aspirated 350-plus-horsepower Mercury EFI combinations when the complete fuel system is correctly designed.
Horsepower support is not guaranteed by the pump alone; actual capacity depends on voltage at the pump, fuel pressure, injector demand, engine RPM, fuel type and the restrictions in the installed system.
Important Fitment Limitations
Some Mercury Laser EFI, XRi, Pro Max and related engines use an engine-mounted vapor separator tank with an internal high-pressure pump. This external pump is not automatically a direct replacement for every VST-mounted pump.
Engines being converted to an external return-style system require the correct plumbing, regulator, filters and electrical controls.
This pump is also not intended as a replacement for Mercury Optimax DFI, Pro XS direct-injection, modern FourStroke or other engine-specific high-pressure fuel modules. Optimax engines use a different fuel-and-air injection system and require the correct model-specific pumps and pressure specifications.
Fuel-Line and Installation Requirements
For maximum performance, supply the pump through a full-flow 1/2-inch inlet line with the pump mounted low and as close to the fuel tank or fuel cell as practical. The inlet side should use smooth, sweeping hose bends rather than tight bends, restrictive adapters or sharp 90-degree fittings.
Restrictions before the pump can reduce available inlet pressure and promote cavitation, vapor formation and aeration. These conditions can reduce flow, increase pump noise, destabilize fuel pressure and shorten pump life. Use a high-capacity prefilter on the inlet side and an EFI-rated fine filter after the pump, with both filters sized for the required flow.
The return line and regulator must also be large enough to bypass excess fuel without creating unwanted pressure. After installation, verify fuel pressure at the rail while the engine is operating under load. Static pressure at idle or with the key on does not confirm that the system can maintain pressure at wide-open throttle.
Final Technical Summary
The Buckshot Racing #77 Mercury EFI fuel pump combines high flow with strong pressure capability for properly configured Mercury 2.4L and 2.5L external-pump EFI systems.
Its published output of 300 LPH at 43 PSI and 13.5 volts, 255 LPH at 43 PSI and 12 volts, and 200 LPH at 75 PSI and 12 volts provides useful capacity for Mercury Laser/XRi, Bridgeport, 260 EFI, 280 ROS, 300 Drag and S3000 applications.
Reliable operation depends on more than pump size. A full-flow 1/2-inch inlet, smooth hose routing, high-capacity filters, a return-style regulator, properly sized wiring and stable voltage at the pump are essential for maintaining consistent rail pressure during wide-open-throttle and racing operation.
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