Bob,
My comments on our informal "filter study" were not intended to
specifically address your question about oil pressure changes based
on Fram filters, they were meant to show that there is a difference
in quality out there. The quality difference is not limited to the
anti-drainback valve, either. The Fram uses a single layer pleat and
cardboard end caps on the filter element, whereas the Unipart and Wix
designs are much heftier.
Indeed, the use of Fram filters in the "hang down" mode would not
require an anti-drainback valve. In fact, that's the orientation of
the filter in my factory GT V-8. The big problem is when they are
installed inverted, like on most late 4-cylinder Bs. At least BL
put in a standpipe to reduce the drainback through the outlet.
The MGC filter installation (also used on 1968-69 Bs) is really
lousy. The had NO standpipe and NO anti-drainback valve. If I were
not interested in concours originality, I would try to replace that
style filter with a remote "hang down" installation.
Maybe the single thickness of the Fram filter media has less
resistance to flow, therefore dropping the pressure a bit. The ideal
situation would be some resistance from a good filter element, with a
relief valve if the filter clogs up.
Here's a test. Get one of the old style cartridge type filter
assemblies used on 1962-67 Bs, and install it without the filter
element. Warm up the engine and check the oil pressure. Now you have
a reference point for what the pressure would be with no filter media
resistance. Compare it to your Fram and Wix data points, and see how
it looks. Couldn't hurt.
Cheers,
Paul (always curious) Kile
Paul D. Kile
kile_paul@aphub.aerojetpd.com
(916) 355-5162
GenCorp Aerojet
POB 13222
Dept 5784 Building 20019
Sacramento, California 95813-6000
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