Two problems with street use.
These regulators don't have the provision for manifold pressure, (vacuum)
compensation making for rich mixture during part throttle deceleration.
Fuel mixture needs to be ultimately controlled by the O2 sensor circuit.
Increased pressure only works once you override the O2 sensor control.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Don Hanson
Sent: Wednesday, August 28, 2013 1:00 AM
To: vanagon@GERRY.VANAGON.COM
Subject: adjustable rate fuel pressure regulator?...anyone tried one with
Digifant?

   I am no engine guy.   When I raced, I had an Engine Guy do my work and
one of the things that always got about 10-20 more HP (out of ~420rwhp) on
our dyno tuning days was a 'rising rate fuel pressure regulator" that he
always tweeked and made more power.   I assume it was changing the spray
pattern on the injectors, or something...

  Wonder if one, taken to the dyno and tuned,  would add power to a VW
motor?   I think the 928 I raced was a type of motronic similar to our
vehicles...

  They would do a pull then "add three flats"(turn the adjuster nut) to the
fuel pressure regulator setting and do another run...after about 5 runs they
wouldn't be getting any more power, so we'd call it good....and out would
come my checkbook, then away to the track...