Modifying Big Bore Kits usually increases the engine displacement by 20%-40%, which requires the simultaneous upgrade of the flow and pressure of the Fuel Pump. For example, after the Harley-Davidson Twin Cam 96 engine was expanded to 103 cubic inches, the fuel demand increased from 4.8 L/min to 6.2 L/min. If the original factory fuel pump (flow rate 5.5 L/min, pressure 50 psi) was used, the air-fuel ratio would deviate from the ideal value of 12.5:1 to 14:1. It leads to a power loss of 8% to 12% and may even trigger a detonation. According to the test data from S&S Cycle, upgrading high-flow fuel pumps (such as the Bosch 044 series, with a flow rate of 7.5 L/min and a pressure of 58 psi) can increase horsepower by 15% and reduce the fuel injection error rate from ±5% to ±2%.
The high-pressure direct injection system puts forward higher requirements for the performance of fuel pumps. Take the modification of Honda CBR1000RR-R as an example. When equipped with a 78 mm large-bore piston, the direct injection pressure in the cylinder needs to be increased from 150 bar to more than 200 bar. The plunger diameter (8 mm) and stroke (6 mm) of the original fuel pump cannot meet the flow requirements, resulting in a fuel shortage rate as high as 18% under high-speed working conditions. The adoption of the Denso 280 L/h high-pressure fuel pump (with a plunger diameter of 10 mm and a stroke of 8 mm) can improve the stability of fuel supply by 30%, shorten the pulse width of the fuel injector from 12 ms to 9 ms, and increase the throttle response speed by 22%. The MotoGP technology transformation case shows that after the racing fuel pump of the Ducati Desmosedici GP23 was expanded to 1000 cc, the flow rate increased from 260 L/h to 320 L/h, the peak pressure reached 250 bar, and the air-fuel ratio fluctuation under the turbocharging condition was controlled within ±0.8%.
The cost-benefit analysis shows the necessity of upgrading the Fuel Pump. Take the modification of Yamaha MT-07 as an example. If the fuel pump is not upgraded simultaneously (the original factory cost is about 120 US dollars), the probability of piston ring wear due to insufficient fuel supply increases by 35%, and the maintenance cost may exceed 800 US dollars. The installation of the Walbro 255 L/h fuel pump (priced at $200- $250) can reduce the load current of the fuel system from 9A to 6.5A, decrease the motor temperature rise by 20°C, and extend the service life to 80,000 kilometers. Industry statistics show that in vehicles that have undergone cylinder expansion and modification, 23% of engine failures are due to insufficient performance of the fuel pump. After the upgrade, the failure rate can be reduced by 42%, and the investment payback period is approximately 1.2 years. Furthermore, the AEM 340 L/h electronic fuel pump reduces the idle flow rate from 40 L/h to 25 L/h through the integration of the PWM control module, improving fuel economy by 5%-7%.
Technological innovation is reshaping the matching standards of fuel pumps and cylinder expansion kits. Bosch’s newly released HDP5 series fuel pumps feature a two-stage impeller design. In engines with a 50% increase in displacement, the flow rate can reach 400 L/h (±1.5% error), and the pressure stability is 18% higher than that of traditional single-stage pumps. In the track package of the Porsche 911 GT3 RS, the fuel pump paired with the 4.2L horizontally opposed six-cylinder engine adopts ceramic-coated bearings, reducing friction loss by 30% and the flow fluctuation rate under extreme working conditions (at a speed of 9000 rpm) is less than 3%. Frost & Sullivan predicts that by 2026, the global market size of high-flow fuel pumps will reach 1.9 billion US dollars. Among them, 60% of the demand comes from the retrofit market. The main driving factors include the annual increase of 12% in the popularity rate of large cylinder diameter kits and the requirements of emission regulations for the accuracy of air-fuel ratio (the error limit is tightened from ±5% to ±3%).