You can try a couple of simple mods. Meister's case pressure increase allows a slight increase, maybe a few hundred RPM more, before the pump drops pressure. You have to modify the "overflow" or "cascade" valve to give more internal case pressure within the pump. Simply increasing the feed pressure (stronger auxiliary pump) does nothing as Ryan mentioned as the cascade valve will still maintain 62psi.
The cascade valve is a simple spring and plunger relief valve, factory set at 62 psi.
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An modified and adjustable cascade valve to increase the pressure will allow a few hundred RPM more stable rail pressure, but is not the only mod for this pump.
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Further increases can be had by increasing the metering valve flow. All the injector fuel passes through these triangular ports in the piston within the metering valve:
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Triangular ports x 3
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You can see the difference in the larger CP4.2 metering valve ports:
Sure, swap metering valves or carefully open up the larger, lower end of the triangle.
These mods together will offer slightly more stable output and rail pressure at higher RPM's, together with Rub's increased duty cycle on the metering valve.
Rub, please share your pump part number. Our American Passat has a slightly longer stroke eccentric shaft, which you may already have?
Meister, all CP4 series pumps have a dual lobe eccentric shaft, offering two strokes per shaft revolution, if that helps answer your question?
All the best!
Andrew
