The performance of the Fuel Pump directly affects the engine’s power output and therefore the top speed of the vehicle. Experimental findings show that if fuel pressure is decreased from the factory default value of 400 kPa to 300 kPa, the turbocharged engine’s power is decreased by 18% (e.g., that of the Volkswagen EA888 Gen3). This lowered the top speed from 250 km/h to 228 km/h (SAE International 2022 Test Report). The BMW M4 Competition example illustrates that where the fuel pump flow is under specification (15% less than the nominal of 140 L/h), the ECU applies the torque limit protection, and the top speed is electronically limited to 275 km/h (the factory design original is 290 km/h). And 80%-100% throttle response delay is extended by 0.4 seconds (BMW Technical Bulletin SI B16 04 23).
The unstable fuel supply caused by fuel pump aging is the predominant reason for rapid attenuation. Statistics from the United States’ NHTSA show that out of the complaints regarding the drastic speed loss due to Fuel Pump failure between the years 2018 and 2023, 37% of the vehicles exhibited fuel pressure fluctuations (±12%) at a speed of more than 180 km/h with the air-fuel ratio outside the theoretical limit by ±0.8 (the standard value ±0.2), resulting in power loss of as much as 22%. In the usual case, since the fuel pump impeller of the 2021 Porsche 911 Carrera S wears out (the flow rate degrades to 78% of the original value), the measured top speed drops from 308 km/h to 287 km/h. And the 100-to-200 km/h acceleration time goes up by 1.2 seconds (track test data from “Auto Motor und Sport”).
The top speed can be increased by the fuel pump upgrade performance. Hondata has done research on the Civic Type R and shown that the Fuel Pump replacement with 30% of flow rate increase (from 130 L/h to 170 L/h) and ECU tuning are able to enable the top speed to exceed the electronic limiter and be increased from 272 km/h to 291 km/h. Meanwhile, the pressure of turbocharging rose from 1.2 Bar to 1.5 Bar (monitored by the data logger). During the Nurburgring circuit test, the Mercedes-Benz AMG GT Black Series employed a two-stage variable displacement fuel pump with a maximum capacity of 200 L/h, with a speed of 325 km/h, which was 7% more than the standard model. The fluctuation rate of fuel pressure was controlled within ±1.5% (±4% for the original pump).
Economic cost analysis shows there is a breakpoint between ultra-fast fuel pump optimization performance and return rate. A 2023 study by the Department of Mechanical Engineering, University of Michigan, said that an increase in the flow rate of a fuel pump by more than 20% of original design means that every 10% more increase in flow rate only brings 1.2% quick gain, while the increase cost reaches 35% (e.g., installing a new fuel line and high-pressure injection system). For example, the Subaru WRX STI owner increased the Fuel Pump flow rate from 150 L/h to 220 L/h and the top speed from 240 km/h to 255 km/h (an increase of 6.25%), but the total modification cost was $1,800 (labor cost included), and the return on investment was only 1:0.3.
Compliance risks should be thoroughly examined. The EU ECE R134 regulation calls for the top speed of mass-produced vehicles not to exceed the tire speed grade (e.g., 300 km/h for Class Y). Modifying the Fuel Pump to cause the vehicle to exceed the limit can invalidate the certification. In a German 2022 TUV penalty case, the owner of an Audi RS6 was found to have illegally modified and was penalized €2,500 for fuel pump upgrading, which resulted in an over 305 km/h top speed (factory original top speed was 250 km/h). The industry advises using the Fuel Pump kit tested to ISO 11452 certification to have electromagnetic compatibility (signal error <0.5%) and mechanical stability (vibration test amplitude <0.3mm).