Listers:
I had many responses to my question regarding the apparent low oil pressure in
my fresh engine. Fully half of you suggested I may have a faulty gauge. Stand
up and take a bow, as you were correct.
I had many replies that included their respective oil pressures from their
Tigers. It is clear to me now that a well built, fresh SBF should have
approximately 35 psi hot at idle, and 45 to 50 psi hot over 2500 rpm. If your
gauge shows much more or less than these numbers, then you most likely have an
inaccurate gauge.
The evidence for the above assertion is mostly anecdotal, but compelling. Here
is what I actually found in tests:
I bought an oil pressure gauge from Paul Breuhan on eBay, and have been taking
some comparative oil pressure readings. I had a test line made up that
connects the gauge to the bottom of my remote oil filter adapter where it
leaves the block. There is a 1/2" NPT plug at the filter feed line and one at
the return line after the filter.
This was really convenient, as I was able to measure the oil pressure where it
comes out of the block before it hits the oil filter, and measure it again
from the other port where it comes out of the filter.
The block pressure right after the pump (where the stock filter reads the
pressure) at 2,000 rpm (hot) was 55 psi. My gauge in the car was reading
approx 40 psi.
The pressure reading after the filter was almost exactly the same as before
the filter, just a little below the 55 psi mark.
This didn't really tell me anything about the real pressure from my oil pump,
but did give a fairly accurate indication of the effect the remote oil filter
system has on the pressure getting to the engine internals after the filter -
almost none.
I had a conversation with an engineer at the local Aeroquip shop where I had
my test line made up... I was inquiring about how much I would have to pay for
a gauge with any degree of accuracy. He said they have gauges that are
oil-filled, and have a zero-100 psi range that they sell for about $75.00, but
that are not certifiable. (No sense taking one to a certification shop and
have it checked because they are so wildly unreliable.) He said they don't
call them pressure "gauges" - they call them pressure "indicators" and they
will often read 15 - to 20 psi different from each other on a line manifold.
At minimum, a gauge with any accuracy and that is certified would cost at
minimum $200 - $250.
Its not likely that the gauges Lord Rootes put on his cars were even as
accurate or reliable as the "un-certifiable" units.
So it looks like the different pressure readings being reported on the Tiger
List can in some respect be attributed to the relative inaccuracy of our
less-than-certifiable and likely very inexpensive stock gauges. I would think,
considering the money being spent on quality parts and assembly by most
listers, that oil pressures would be relatively similar from block to block,
and until someone checks a fresh, well built engine with a certified gauge, we
will not know what a good, accurate pressure reading should be.
I would be really happy with somewhere in the 50 psi range cold, and 35 to 40
hot at idle. I think I have that. I just didn't have a gauge that said so
until I got Paul's gauge. And who is to say his is or is not accurate? I had
my rotating assembly built and balanced by a reputable speed shop in New
Mexico. It was installed by a second mechanic who was a good parts replacer if
nothing else, and it was checked again by a shop that builds engines for many
NHRA and Nascar teams. It was pronounced fit and good to go. I have had two
new oil pumps in the pan, a high volume and a standard, and both read the same
on my in-dash gauge.
I think we can safely say that only substantial engine wear will affect oil
pressure readings. (Several respondents have engines with 100,000 to 200,000
miles on them with oil pressures in the above range).
Also, a well designed and assembled remote filter with AN8 lines will not
cause a substantial drop in pressure. (Mine showed only a 2 or 3 psi change).
An oil pump in good condition will make the same pressure as another oil pump
of equal condition. My oil pressure readings did not change appreciably from
the one in my car when I bought it with a well worn engine - through a rebuild
and a new hi-volume Melling pump, to a standard Melling pump currently
residing inside my oil pan).
So I am going to stick the 55 psi gauge in my dash and move on.
(Thanks Paul!)
Life is good when your o.p. gauge reads right where you want it. (regardless
of the real oil pressure! (O:) )
Dave
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