Ahhh, data!  Nice job.  Contribution to JVV reviewed and accepted.

I'll repost the data I collected from my used fuel pressure regulator (FPR)
for comparison:

applied vacuum  Michael, new FPR        Michael, used FPR       Scott, used FPR
("Hg)           (psig)          (psig)          (psig)
15              31              32              29
0 (atmosphere)  38              39              37

The conclusion I would draw is that if one is unsatisfied with their FPR
performance (i.e. because it
doesn't meet the specs in Bentley) they should think twice before buying a
new FPR.  In this statistically
challenged study of 3 FPRs, an idle manifold vacuum greater than or equal
to 15" Hg was required for
the FPR to meet the Bentley spec (and one of these FPRs was brand new).
Anecdotal evidence from the list
suggests that 10-12" Hg is a more typical manifold vacuum at idle for our
engines (although Jay Snyder has
reported 15" Hg for his engine).

The MityVac tool (a hand-actuated vacuum pump) Michael refers to below is
pretty useful for diagnosing engine problems.
I bought the model with the gauge (a key feature) from HarborFreightTools
for around $50.

Scott Terry
'85 Westy "Pearl"
Santa Barbara, CA

>Hi all,
>
>Well, I finally replaced my fuel injectors and fuel pressure regulator.  I
>thought that I would publish my measurements for inclusion into Scott's JVV
>(Journal of Vanagon Vacuum -- It really sucks!).  I don't know the ambient
>pressure at the time of measurement -- Durham is in the middle NC, halfway
>between the coast and the mountains, so it is probably a nice average.  My
>vacuum guage read 13" Hg with an eyeball rms average.  My original fuel
>pressure regulator measured (with Robert's guage -- uncalibrated) 32 psig
>with the vacuum and 39 without.  My new Bosch fuel pressure regulator read
>31 with the vacuum and 38 without.  Still a little high, and not much
>different then the old one.  Maybe I wasted my money.  Oh well, at least I
>have a spare now.  For fun, I hooked my (uncalibrated) Mity Vac hand pump
>and guage directly to the fuel pressure regulator, and noted the fuel
>pressure to see what it would take to get down to 29 psig:
>
>"Hg            psig
>22             29
>17             30
>15             31
>
>Michael Townsend
>Durham NC
>90 Carat