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Old 01-09-2009, 12:52 PM
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SBC HVP oil pump, low pressure

ok, ive built engines for years, but i have my own problems with a new motor i put together recently. the oil pump i have in my 350 4 bolt is supposed to be a hi volume pump but only puts out about 35-40 lbs when cold and is terrifyingly low when warmed up, only about 15-20 lbs.
my inline 6 has a hi volume pump in it and has 75 lbs when cold and 35-40 when warm. what am i missing here? do i have a bad pump or what? do they even sell a hi pressure pump and hi volume? and what kind of psi difference should i be seeing? i dont want to hurt this motor., and i dont have the money to go back into it if i kill it. thx for the help

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Old 01-09-2009, 12:55 PM
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What's the part number on the oil pump box - if you still have it?

What is the pressure at WOT or 5,000rpm when hot?
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Old 01-09-2009, 01:14 PM
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That is the exact problem I had on my 307. It turn out to be a bad distributor. It turn out the bottom part of the housing on the groove oil travel around it, then into the lifter gallery. It did not seal properly, and it leaked back into the oil pan. Let me tell ya, It was pain in butt looking for that low oil pressure. I replaced all the bearings and still the oil pressure very low. The pressure read 50-60 psi cold, and 5 -10 hot at idle. After replacing the distributor the oil pressure jumped to 80 psi cold 40 psi hot at idle.
Hope this will help you.
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Old 01-09-2009, 01:34 PM
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Here's some pump mods that can be done for performance and other Info. Used to be another good article with pics on another site but Pics are gone.
http://www.chevytech.com/2c63.html
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Old 01-09-2009, 02:37 PM
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"where" is the sender reading psi on the oil galleys does change the readings....

sounds like your reading the psi after the mains "and" cam bearings leakage PSI loss....

if it is only 15-20 at say 3000rpm, there is a problem
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Old 01-09-2009, 03:15 PM
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im still getting pressure rise on engine revs, but mayb e only about 10 psi. the car came with a 307 and the distributor is straight out of that engine which is an hei i slapped in a few years ago to get rid of the old points style it origonally came with. and the 307 had good oil psi. 55 cold and 25-30 hot idling. the only thing different is the arp pump shaft that i bought at a local performance shop.
the sender is in the same spot as the 307 next to the distributor. the engines bottom end is completely rebuilt, and i trust the man (ive known him for years and is quite competent at engine machine work and building), who not only did the machine work (.040 over), but assembled the short block as well. the engine was given to me when the shop changed hands from being an auto machine shop to a transmission shop and the owner was clearing out the leftover engine parts and all to make room for all the equipment and all needed to run a proficient transmission shop.
so at least at this point you all can understand why the oil pump i had obtained is questionable. it belonged to someone else i knew and not that i didnt trust him, but i still opened it up and checked to make sure all was ok, which from what i could tell did. the only thing i didnt check out was the regulator for psi. im sure this is the issue, but i know there are others out there who have more info and knowledge of oil pumps than i do which is why i brought this up... thx for all the info and help.
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Old 01-09-2009, 03:24 PM
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i hope its not a melling m55hv pump. they castings were changed few years ago and they crack. melling doesn't recomend or warrantythem for anything besides a stock engine
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Old 01-09-2009, 06:08 PM
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RARELY the oil pump is at fault. How much hot idle oil pressure? How much at cruise RPM? Mechanical or electric oil pressure guage? Are you sure it is good?

Are the front oil galley plugs sealing? Are the main/rod bearing clearances correct? New cam bearings? Are they installed correctly? If any of the groove behind the cam bearing is uncovered.....pressure will bleed by.
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Old 01-10-2009, 07:23 AM
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test with the oil psi guage off the I6 motor...
next test, swap on a new regular mellings pump....

still reads low=parts error or build mistake in the rebuild
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Old 01-10-2009, 10:26 AM
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forgot...

do check that the pump mount bolts are not to long,,,
botteming out and not truly sealing the pump to the block surface...
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Old 01-10-2009, 12:42 PM
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What was the oil pressure before you added the HV pump?
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Old 01-10-2009, 05:07 PM
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this is a fresh .040 engine. the builder i know and have known for roughly 20+ years and have installed his engines before and have had no issues. the gauge is the same as from when the 307 was in the car and its a mechanical gauge.
the pump was used., but was told it was ok. mind you, i mentioned above the cold and hot pressures all at idle in gear and what the pressure rise was at cruise...
the one thing that i did notice was about the front galley plugs, which in all honesty, i thought were all there and the guy who assembled it told me he cleaned out all the oil galleys and always replaces with new on assembly, and usually rechecks all his work with a fine tooth comb so to speak. as far as clearance, i didnt check that because like a said this was a pre-assembled short block that was built .040 and given to me when ownership changed hands from the machine shop that it used to be to a transmission shop that i was shop foreman for. a stock oem pump is only 20 bucks, its gonna have to wait till the money starts coming back in, and for that matter the car can sit till then or till i get my taxes done because, at that time im also going to be putting in new diff gears and a lock-right locker setup to use it for drag racing. the motor with a stock cam still screams and with the 700r4 i built for it is an amazing difference from the old stock 307/th350 combo it used to have and at that time with the car having 3.08 gears still ran consistent 10.00's and has run a best of 9.88 in the 8th mile. and the only things on the 307 was a factory aluminum intake, same hei thats in the 350 now, and a jegster header-back exhaust kit i bought when i saw how chocked up the 307 was with the factory exhaust.
im not looking to go any quicker than low 8's in the 8th, cause if i break into the 7's, i gotta put a cage in and i dont want to do that and i still want to keep the car streetable to a degree.
1 of the reasons i built the 700r4 for it. and yes its pretty damn stout and will hold, and i got rid of lockup so theres 1 less thing to fail ( ive had a 700r4 built the same in my 76 with a inline 6 that my dad and i put together in 1996). it works flawlessly and has over 150,000 miles on it since then and, with no lockup, i have absolutely no sediment in the pan on services like i normally see on 700's with lockup.
anyway, i hope you can see that im quite particular about how i do things, and try to take the most care in what i do to ensure that what i have lasts.
again, i still appreciate all the comments and suggestions, thats why i still come around here. its been a great site to help and be helped with on my own problems. cheers!

p.s.
when i do pull the motor back out i will be checking clearances and everything else just to be sure, you can count on that.
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Old 01-11-2009, 11:14 PM
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Old 01-12-2009, 06:12 AM
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coolio, i have already gotten more than i really expected in the 1st place. lol.
it was more curiosity than anything, cause with what i had mentioned, im going to be pulling the motor back out to investigate and make sure everything is in check. im like everyone else, i dont know it all, and i could always learn from others that have been through this kind of scenario to where this is a first for me... rock on hotrodders!
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Old 01-12-2009, 05:28 PM
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Be sure to post back what you find. It may help someone down the road.
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