Mercury 2.5L + 044 Pumps Flow Rates
- Mike Hill
- 1 day ago
- 3 min read
The Buckshot Racing #77 EFI fuel pump, a high-performance Bosch 044-style replacement, is widely trusted for demanding EFI applications in marine and motorsport environments.
The spec flow rates for the pump are 79 GPH (300 LPH) at 43 PSI and 13.5 volts, 67 GPH (255 LPH) at 43 PSI and 12 volts, and 53 GPH (200 LPH) at 75 PSI and 12 volts. These values reflect real-world performance across different voltage conditions.
Since electrical system voltage varies depending on battery chemistry—lead-acid batteries average 12.4–12.6V, AGM batteries around 12.7V, and lithium iron phosphate (LiFePO4) batteries often sit between 13.0–13.4V—this evaluation assumes a practical baseline of 12.7 volts to reflect common high performance use.
At 12.7V and 43 PSI, the 044-style pump is estimated to flow approximately 71 GPH (270 LPH). Like all electric fuel pumps, its flow rate decreases as pressure increases, typically by 10–15% per 10 PSI.
Understanding this pressure-flow relationship is essential for designing fuel systems for Mercury 2.5L EFI engines, which vary in both fuel pressure and volume depending on model and modification level. Below are a few examples.
The Mercury Marine Laser or XRi type front injected motor requires approximately ~26 GPH (98 LPH) at 33 PSI at wide-open throttle (WOT).
At this relatively low pressure, the Buckshot #77 pump outputs over 74 GPH (280+ LPH), offering nearly 3× the required flow, ensuring excellent injector supply and pressure stability under load.
The Mercury Racing 260 EFI demands slightly more fuel at WOT, requiring ~28 GPH (106 LPH) at 39 PSI.
At this pressure, the pump continues to deliver around 70–71 GPH (265–270 LPH) at 12.7V, again offering a safe 2.5× flow margin, suitable for high-performance recreational and competition use.
The Mercury Race 280 ROS, 300 Drag, and S3000 versions require a higher flow of ~30 GPH (114 LPH) at 56 PSI, pushing the system closer to the high-pressure limit of the pump.
At this pressure, flow output is estimated at 58–61 GPH (220–230 LPH). The pump provides roughly 2× the required fuel volume, ensuring consistent WOT operation with solid headroom.
For heavily modified Mercury 2.5L engines producing 350+ horsepower, estimated fuel demand rises to ~35 GPH (132 LPH) at approximately 56 PSI, depending on porting, RPM range, and final tune.
In this case, the 044-style pump, delivering ~60 GPH (220–230 LPH), offers around 70–75% flow overhead, which is generally acceptable for high-output naturally aspirated builds.
For ultra-high-performance, a ~110 GPH (400LPH+) pump setup may be more suitable to maintain safe injector pressure and flow margin.
In conclusion, the Buckshot Racing #77 EFI pump provides robust flow performance across a wide range of pressure and voltage conditions.
With a real-world baseline output of 71 GPH (270 LPH) at 12.7V and 43 PSI, it is fully capable of supporting all Mercury 2.5L EFI variants—whether it's a stock Laser XRi, a tuned 260 ROS, a high-pressure 300 Drag, and would support fully built 350+ HP motor with the 1/2" input, no bends and no 90 degree fittings are recommended.
We would soft bends on your fuel hose to reduce flow distribution including airation in the lines that can be caused by hard bends.
With proper voltage management, high flow filtrs, and return-style fuel regulation, this pump delivers consistent performance and headroom even under wide-open throttle and race conditions.
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