[DeTomaso] High-Anything Ford Oil Pumps

[Tony DiGiovanna]

Jack,
First, thank you, a million times over, for all your shade-tree articles in
the POCA newsletters.  I enjoy them immensely and know they are the result
of endless hours of thought, persistence, inquisitiveness in the garage and
behind the keyboard.

I was reading the one in this September's newsletter regarding high-pressure
and high-volume oil pumps.  I'd like to add my thinking to the perplexing
rev-limiting phenomenon reported by some, although I recognize I have no
definitive answers...

>From what I think I know of positive displacement pumps and hydraulics, I
believe a pump that is restricted by an orifice does not exhibit either
cavitation or surge.  Cavitation is experienced at a location where there is
a sudden drop in pressure.  Surge is a phenomenon associated primarily with
compressible flows and centrifugal pumps at low flows.  The only phenomena I
would expect by heavily restricting the flow out of a high volume/pressure
oil pump is high pressure and high input shaft load.  Furthermore, the power
loss shown in the dyno curve is around 100HP at 6000RPM.  I would expect any
mechanical source of 100HP loss to result in obvious problems, like severe
heat damage and broken parts in short order.

Therefore I postulate the rev-limiting to be a phenomenon associated with
oil-pressure related valve train performance.  i.e. the engine is making
100HP less, not dissipating it somewhere internally.  It's not clear from
the article what kind of lifters are in Liebenow's engine.  Could excess oil
pressure lead to valve "float" by way of pumping up hydraulic lifters or by
defeating valve lash in solid lifters??

Food for thought.  Comments welcome.

Best Regards,
Tony "always uses std pumps with no problems" DiGiovanna