Modification of the 2.0T FSI engine far beyond OEM power levels requires an additional volume of high-pressure fuel especially in the midrange (3000-5000rpm) of the powerband. To understand why this fuel is needed for the mid range, one must first understand how the fuel delivery system works in the 2.0T FSI.
APR High Pressure Fuel Pump Internal Parts
A low pressure fuel pump, which varies from ~40-95psi, delivers fuel from the gas tank to the high pressure fuel pump. Then the high pressure, camshaft driven pump pressurizes the fuel to upwards of 130bar (almost 1900psi!) in order to spray fuel directly into the combustion chamber. Unfortunately on cars that have many modifications, the stock fuel pump cannot flow enough volume of fuel to maintain the system pressure and the car suffers from the familiar "fuel cut" that so many modified customers experience.
The limitation of how much volume of fuel the high pressure pump can flow is dependent upon the volume displaced by the pressurizing cylinder inside the pump and the number of times the piston reciprocates inside that cylinder. Since the high pressure pump isdriven off of the engine camshaft by a three lobe cam the piston of the pump cycles at 1.5 times the engine rpm. (Engine camshaft turns atone-half engine rpm multiplied by three for the number of lobes on the high pressure cam lobe).
Due to this dependency on engine rpm for the high pressure fuel pump output volume, the FSI pump is capable of flowing almost 370hp at7000 rpm but only 158hp at 3000rpm. The graph below illustrates the maximum horsepower potential of the stock fuel pump compared to the APR FSI fuel pump. Also on the graph are stock and APR Stage III horsepower numbers. Clearly, the stock pump is insufficient for the output generated by this upgraded kit. The only way to address this issue while maintaining a pump that fits in the stock location isto change the volume of the pump's internal pressurization chamber.
Fuel Pump Potential
In order to address the lack of fuel in the mid range, the APR FSI fuel pump increases the volume of fuel from the high pressure pumpby over 40%. Simplified, this is achieved by modifying some key internal parts within the pump. Changing these components requires precision machining of the new components with special surface treatments as well as enlarged, redesigned seals. Using inferior components on this critical part can lead to many problems from gasoline in the engine oil(from a bad seal) to complete engine failure (from a seized piston in the high pressure pump).
To give an idea of the tolerances involved, the final surface finish on the piston inside the fuel pump is so critical that it can be damaged by touching them with bare hands. The tolerances between the piston and the new barrel the piston rides in can only be measured by a multi-million dollar machine which uses air volumes to measure the part clearances to within microscopic levels.
Fuel Pump Components
The components used in the APR pump are also of a high caliber. The piston and barrel of the new pump are made of a certified and heat-treated bearing-grade stainless steel and have a special diamond like coating. The seals used in the pump are made of a high performance, filled polymer with a high modulus spring to retain the seal forces throughout the life of the product. The cross section of the seal is also of a proprietary design to maintain integrity over many years of use.
APR FSI pumps have been track tested since 2006 with several hundreds of thousands of miles of combined usage. Each APR pump starts out as a brand new OEM pump and is then modified with the new components by APR and undergoes a rigorous testing process on our high pressure fuel pump tester. Once a pump passes our standards it is serialized and shipped to the customer.
When it comes to a critical component that can mean the difference between winning a race and not finishing at all, motorsport teams must use the best components available. Motorsport teams around the world have put the APR High Pressure Fuel Pump though brutal and demanding testing and have proven again and again there liability and performance you can expect from each and every APR High Pressure Fuel Pump. The initial success of the R-GTI and APR's own motorsport team have lead other noteworthy teams around the world to rely on APR.
A second option is to send your existing HPFP to APR. Your pump will be tested, cleaned, rebuilt, tested again, broken in, serialized, and shipped back to you the same day! In most circumstances barring unusual occurances.