oil pumps (not efi)

[Darrell Norquay]

At 07:20 AM 12/11/96 -0600, Tom Cloud wrote:

>The high volume pump does not increase pressure, so no more oil
>flows through the engine than for a normal pump, unless there's
>a loose fitting or such, right?

A high volume pump will, in fact, increase oil pressure in most cases. I say
in most cases since if bearing clearances are loose, it may not increase
pressure over stock, but it will have higher pressure over a stock pump,
which would be below normal in this case.  This is a band-aid solution,
however, if the engine has proper clearances, the high volume pump will not
be necessary.

> - same volume of oil will be pumped by stock and hi-vol pump (i.e.
>hi-vol pump will just recirculate and 'froth' the oil).  The only
>time the hi-vol capability will be needed is when the engine is
>very old or has an internal 'leak'.

WRONG.  Why the heck would it be called a high volume pump if it didn't pump
more volume per revolution?!?!?  If you carefully compare the stock pump
with a high volume pump, you will note the body of the pump is longer,
denoting longer gears in the pump, and thus more swept area of the rotors.
More area x same RPM = higher volume.  This will equate to higher average
oil pressure, all else being equal.  The only circumstance the oil pump
recirculates is if the filter is allowed to clog up, at which point there is
a bypass valve in the block which still allows oil to circulate, albeit
unfiltered.

> - you are advised to buy a hardened, stronger oil pump drive shaft
>when you get a hi-vol pump ...... this implies to me that there's
>more of a load on the shaft, hence on the cam gears, on the cam
>'bearings',on the timing chain and gears.  Why would you do that?

The increased load is proportional to RPM.  If you plan on redlining the
engine at 8000 RPM, I would recommend the hardened shaft, if you don't plan
on running above 5500 or 6000 RPM, don't bother. 

> - my 302 in my F150 with 107,918 (as of this morning) reads very >near the
same oil pressure it did when it was new (on the "A" of >"NORMAL", heh-heh).
It does this even when hot, down a quart and at >idle of 650 rpm (once
again, as of this morn).

All this means is that your engine is still in reasonable shape internally.
A high volume pump doesn't last any longer than a stock pump under the same
conditions.  

>Neither my mentor/guru nor my part$ guru could tell me why I should
>use a high volume pump.  Seems to me to really just be a waste of
>_precious_ horsepower and a source of unnecessary wear on the cam
>and related components.

This is true.  Having cleared up a few inconsistencies in your above
comments, there are very few reasons to use a high volume pump. To quote
David Vizard (How to Build Horsepower, S-A Design Books):

"Most stock oil pumps supply sufficient oil flow for modified street engines."

"In most engines, abnormally high oil pressure (above 45-50 PSI), increases
pump drag, absorbs engine power, increases the chance of oil entering the
combustion chambers, and does not provide improved bearing lubrication or
extend component life."

"Higher oil pressure will almost always do only one thing: rob horsepower,
often as much as 10-15 HP when pressures of 100 PSI are used."

BTW, don't even think of re-using the old pump.
regards
dn
dnorquay at iul-ccs.com