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?