How to Install Rear Oil Pressure Gage

by Dave Knutsen

To attain a more reliable location for taking the oil pressure signal there
is a very simple process as follows(see photos below for more detail):

Drill about a 3/4" diameter hole in the flat web section in the center rear
of the block,just at the block and trans parting line. Using this hole as
an access hole, then drill and tap a hole for 1/8" NPT (National Pipe
Thread) in the passenger side oil gallery just in front of the rear threaded
1/4" pipe plug. Once this hole is drilled and tapped insert a brass 1/8"
by 3" or 4" pipe nipple with a good pipe sealant, preferably a non hardening
paste with teflon. The end of the nipple will extend out of the hole in
the web area and you can attach either an electric sending unit or a fitting
and steel braided line for a mechanical gauge. As a 10 to 15 lb.
difference exists between the front and rear of the block, this will give a
much more accurate reading of oil pressure going to the #5 main bearing.
A general rule of thumb is 10 lbs. of pressure per 1,000 rpm. As with any
modifications involving drilling or grinding, a very thorough cleaning and
deburring will be in order.

Another Solution

By Richard Henderson

I found another way to do the rear oil pressure gauge. I used a short elbow that I bought at the local napa and screwed it into the rear galley plug instead of drilling it in like Dave Knutsen. Napa has both the short and the regular 90 fittings.
Dave and I are good friends, and we talked about it first. He said that he didn't do that because he thought of clearance problems with the flywheel. I can tell you and you can look at the pictures that there is no problem at all. More than 1/2 inch clearance.
It is a lot easier, and no chance of getting any metal shavings into the motor. I still would recommend the stainless steel line braided line though. I have been running it this way in my car for over 4 months now. Also instead of running the line up the top, I ran it horizontally out the side and put a little silicone to keep it from vibrating on the block.