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APR FSI High Pressure Fuel Pump |
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| While modifying the 2.0T FSI
engine beyond factory power levels, it became quickly apparent that
an additional volume of high-pressure fuel was needed to make horsepower,
especially in the midrange (3000-5000rpm) of the powerband. To understand
why this fuel is needed for the midrange, one must first understand
how the fuel delivery system works in the 2.0T. A low pressure fuel pump (which varies from ~40-95psi) delivers fuel from the gas tank to the engine. Then, in order to spray fuel directly into the combustion chamber, a high-pressure, camshaft-driven pump pressurizes the fuel to upwards of 130bar (almost 1900psi !). 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 gets 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 dependant 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 is driven 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 at one-half engine rpm multiplied by three for the number of lobes on the high pressure cam lobe). Because of this dependency on engine rpm for the high pressure fuel pump output volume, the FSI pump is capable of flowing almost 370hp at 7000 rpm, but yet 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 is to change the volume of the pump’s internal pressurization chamber. |
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| In order to address the lack of fuel
in the midrange, the APR FSI fuel pump increases the volume of fuel
from the high pressure pump by 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. 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 for over a year now, with several hundreds of thousands of miles of combined usage. Each APR pump starts out as a brand new OEM pump, is modified with the new components by APR, and then 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. The APR fuel pump tester is a key element in the APR fuel pump production process. With the fuel pump tester, we are able to perform several tests to ensure every pump is working to the high standards we have set for it. First, the fuel pump tester allows us to perform the critical initial break-in of the new pump. Also, by bringing the pump up to the full operating pressure, we can confirm that the seals in the pump are properly installed and not leaking. Finally, a performance test is performed to make sure that the pump output is within specifications. This level of quality control ensures a lifetime of worry free miles with an APR FSI high pressure pump. The APR 2.0T FSI fuel pump requires APR engine management recalibration to allow for the increased size of the APR fuel pump to ensure flawless drivability and is included with your purchase. Currently, some APR Stage II and K04 turbocharger clients will be able to take advantage of increased horsepower and torque up to 25hp and 35lb ft with APR fuel pump specific engine management performance recalibrations. |
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