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

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW