----- Original Message -----
Sent: Thursday, September 21, 2006 12:57
PM
Subject: [FlyRotary] Fuel Pressure
Regulator Vacuum or Boost??
For the entire life of my rotary powered RV-6A, I have
flown with a "Boost Referenced" adjustable fuel pressure regulator from
MSD. As you know, it is desirable to keep the pressure differential
between the injector fuel rail pressure and the manifold pressure a constant
for best fuel injection control.
I flew for several years thinking that since my pressure
regulator was manifold reference that it was indeed doing this. Then the
light bulb came on - my fuel pressure holds rock-steady at 43 PSI - and does
not vary between idle and WOT! This certainly implies that the fuel
pressure IS NOT varying as a function of manifold pressure.
Then doing some recent research on fuel pressure
regulators, I noticed that some say they are "Boost Referenced" and other's
say "Vacuum/Boost Referenced". My conclusion (which may be
incorrect) is that while my pressure regulator is "Boost Referenced" it
is not "Vacuum Referenced". The difference (If I understand it correctly
) is that my regulator would increase fuel pressure IF it ever encounter
manifold pressure greater than ambient - since I am not used forced induction
that never happens - which in turn appears to be the reason I never see the
fuel pressure changing in response to manifold "vacuum".
So my question to those who realllllllyyyyyy know -
is it correct that for my NA 13B I need a fuel pressure regulator that
responses to manifold "Vacuum" or is the difference in description between
"vacuum referenced and boost referenced " just semantics in
advertising?
Thanks
Ed