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...