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BBC oil pressure port

5K views 18 replies 5 participants last post by  chasracer 
#1 ·
Is the larger plugged port above the oil filter a good spot to check oil pressure? If so, does anyone know what size pipe thread that is? I should have done this during the last oil change but forgot. I'd like to have the adapter to my low pressure idiot light switch (on at 30lbs.) I do have a gauge hooked up to a small port close to the front but I'm sort of curious how much higher the pressure it back near the pump. May have to run a temporary gauge to that port and run it until it's hot and see how low it goes. Sad to say my front port is going down to 30 when running hot at idle in gear.
 
#2 ·
The last big block I had, I put my line in at the oil filter,
but cannot remember the size fitting used. In my opinion
you should get the near the same reading at both
places, and I don't think 30 lb pressure at hot idle is anything
to worry about.
 
#3 ·
the port is 1/2"npt that is the location your guage should be hooked to. the fwd ports are not there for gauges, they are there for machining the passages in the block.
honestly 30psi hot idling is very good. What grade oil are you running ??
 
#4 ·
OK, I don't know why but for some reason I had the gauge up in the front port from the start years ago. Thing is that it lost almost 10lbs at hot idle since the rebuild. Just got back from a test drive after thrashing it a bit on the interstate and it was down to 27lbs. It does go right up to about 45lbs at about 1000 rpm and hovers somewhere around 50-55 at higher revs. And it is a stock Melling pump ... with the "corvette spring". Should I have changed the pump with the rebuild? It only had 11,000 miles on it. I suppose I should have at least opened it up and looked inside. Still have the high volume high pressure pump that was in it originally on the shelf. That one was shooting the oil over and missing the rockers. Oh the oil, dang I forget what I had in it at first but since the pressure was lower than before, I filled it with straight 30W.
 
#5 ·
your pressures are normal for a stock pump and 30wt oil. oil pressure is somewhat governed by bearing clearances. Do you recall what your rod and main clearances are?? also what is the side clearance on the rods??
 
#6 ·
Sorry no I don't remember any of those clearances. I wanted a higher than stock idiot light in addition to the gauge and I guess 30lbs was a little too high. I think the stock ones don't warn you until it down to about 7lbs if I remember correctly. Wow just looked at Summit, it doesn't show the pressure for my light, but they have some that don't light until below 3 psi!
 
#8 ·
both of mine are 1/2npt, but then again they are factory high hp corvette blocks .
 
#9 ·
Hmm, isn't that odd? I wonder for what reason they would make them larger? Where do you hook up an oil cooler?

I got a 1/2 to 1/8 adapter at Lowes but they don't carry the 3/8 to 1/8. Last evening I passed my first auto parts store to make it to the one that always has fittings dirt cheap, but they were closed. To Autozone, no. Advance auto, no. Back to O'Rilieys (the place I passed) and this kid was trying to look it up in the computer and asked me for what make and model car. This was after looking at all the Dorman fittings. I told the kid that he won't find it on his computer, just go back to the loose fittings, and I followed him. He found it in about 5 seconds!

By the way, my gauge jumped up about 15lbs. when warmed up in the driveway. Haven't got it out on the highway to see what it shows after it's hot but I think I'll do that now.
 
#10 ·
After 20 or so miles at about 3K, in gear at an idle it came down to 30, the new sending unit flashed the light, then it went up 2 or so lbs and the light stayed off. Although it was cool out, only about 70°. I imagine that oil light will be on at every stop when it's hot out. Maybe should have got a 20psi sending unit.
 
#11 ·
I have my o/p gauge hooked up above the filter. Stock Melling pump,stock spring, 18-20 psi @ 1000 rpm hot. Bearing clearance was set @ .0025 on both rods and mains. From what I've read over the years, 10 psi per 1000 rpm is more than adequate. I was advised NOT to install a high volume pump by my machine shop for the very reason you mentioned. All the oil goes to the top end and starves the bearings.
 
#12 ·
I don't think I ever said that last sentence, I'm certain.
*****
(All the oil goes to the top end and starves the bearings.)
*****
The reason I removed the HVHP pump that the "perfect" machine shop man installed is because it shot the oil over the rockers letting them run dry until they chewed themselves up. I personally think that last sentence is BULL. If you have oil pressure, it's going everywhere, well maybe over the top of some rockers if it's too high, but I see no way possible how all the oil can go to the top and starve the bearings below unless some modifications are done to restrict oil to the bearings.
 
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