Ed;
I started with a
fixed pressure regulator at 42-43#, which would normally be fine for NA.
When I was having trouble getting the engine to idle right with
Tracy’s EC2; he
mentioned that his programming was set up assuming a manifold pressure
referenced regulator. TWM was kind enough to trade me straight across
for one that was pressure referenced – pressure at idle now is low 30’s, and
it helped getting good idle.
I guess “boost
referenced” means just that; for MAP above normal
atmospheric.
Al
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Thursday, September 21, 2006 9:58
AM
To: Rotary motors in
aircraft
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?