As you may remember
, a couple of weeks ago I lost
most oil pressure. I dropped the pan and found the problem.
I safety
wired the culprit
up and put my engine back together and back on the back of the
Velocity and cranked her up and got significant oil pressure as
expected. I could see it pumping freely out a hose I left open when
I cranked the starter with pumps/coils/injectors
off
earlier.
Now, my question is, what is considered correct oil pressure at different
power settings? Before when I ran the engine at idle (on my engine,
usually 1500 - 1650 rpm, my oil pressure would be around 33-35 psi. I
remember this cuz
,
on my EM2
it
is preset to start flashing an alert if the oil pressure goes below 35 psi, so
I was always bumping up the idle a bit to keep it from flashing the
alert.
Now, however, it seems that at about the same RPM I am getting only
about 30 ish
PSI at the same RPM and have to rev up to about 2200 rpm to get the pressure
to 35 or above. IIRC
, when I apply power to about 6200 rpm the pressure goes up
to the mid 50's
or a little more...maybe hitting 60.
I had thought I read somewhere that the EM2
was set to alert on oil at 30, but Tracy
has had my unit a couple/few times, so I am thinking the 35 must
be correct for low pressure.
I am still sorting some final engine details out and this was
noticed.
There are only 2 oil pressure relief pressures used in stock engines.
1971-1991 (All) is 71.1 PSI.
1993-1995 Twin turbo 110 PSI.
The early relief valve can be disassembled and cleaned. Washers may be
added under the spring to increase oil pressure. 80-85 PSI cold would be nice.
Check relief pressure with shop air. Be sure the bleed holes are fully exposed
with the plunger fully compressed. This may be possible with the later (welded)
valve but I have never had one to play with. The pumps are powdered metal, so I
would not go much above 85 PSI for long life.
Unlike most engines, the rotary regulates oil pressure with a relief valve
in a leg near end of the system. So, the lowest pressure fed into the oil filter
stand and thus the filter is the relief pressure. Or, 71.1 pounds. Measuring oil
pressure from the stock locations gives you a reading of how much pressure there
is in the vertical gallery from the Banjo fitting (a flow disaster) to the
filter adaptor. So a pressure drop through the tiny filter is not reported. Keep
in mind you plan to use the engine at nearly 3 times the RPM of the normal
street engine. With 40 or 50 weight conventional oil, or 30 or 40 weight
synthetic you should show the relief pressure right after start up at fast idle
say 1,500 RPM. This with standard day ambient. As oil warms and drainback
improves, oil pressure should be rock steady at about 71 pounds. As oil
temps go up, expect at least a 5 pound loss of pressure due to oil foaming.
The recorded oil pressure is not what the bearings see. All of the bearing
flow is after the filter, so pressure drop in the filter element and galleries
reduces the reported number. The front rotor bearing failures can be attributed
in part to lower oil pressure. Thus in racing both ends of the crank are oiled
with an extra hose.
The other problem is that the top oil gallery is also the top dowel
gallery, and the dowels have threads inside so a puller works. And then 3
drilled 90s. A poor design for flow.
This data and much much more is available for free download from Racing
Beat's web site.
Also the Mazda Competition manual (old and poorly done) is available for
free download from the "Nopistons) web page.
Multigrade conventional oils foam readily, and burn poorly. So, if you must
use the OMP, then a straight weight conventional oil, or better yet, a
conventional racing oil like 40 weight Valvoline. The racing oils have more
Zink antiscuff and more anti foaming agent. If you premix, or have one of
Richard Sohns gadgets to feed the OMP from a container on the firewall, then you
can use a synthetic racing oil in the sump, and an ash free 2 cycle top
oil.
Got to work with a 20B this week. Oil pan and pickup a disaster.
Lynn E. Hanover