Oil Pressure -1975

[Mike Barnard Sr No 36249]

I need a little advise from the experts. I just had a 383 stroker motor built for my 75 driver. The oil pressure guage shows 70lbs. at idle and holds at this after motor is warmed up and at highway speed. I have checked with the shop that built the motor and they say this is ok and will not hurt the motor.
They also told me during our conversation that they installed a high flow oil pump so that is why the pressure is so high. What is any one else's opinion? Do you think this will have any adverse affect on the enternal parts or oil consumption? Thanks in advance for any help.

[Joe L.]

Re: Oil Pressure -1975

Mike-----

A "high flow" (presumably, meaning a high volume) oil pump does not, by itself, increase oil pressure. However, as a practical matter, most, if not all, high volume oil pumps are also high pressure by virtue of the installed pressure relief spring. I've never changed or heard of anyone changing a spring in a high volume pump to a standard pressure and I don't know how that would work out.

Anyway, I regard a high volume and/or high pressure oil pump to be unnecessary for a street small block, including a 383.

70 PSI sounds a little high for a high pressure oil pump with the engine warmed up and at cruise RPM. However, it's in about the expected general range for a high pressure pump. You might also want to install a test gauge to ensure that your present oil pressure gauging system is accurate. 1975 uses an external, engine mounted oil pressure sender which is wire-connected to the dash gauge.

Frankly, at this point, I think your best bet is to just leave the pump as it is. Keep driving it and see if you have any oil consumption or oil leakage problems. If these develop, then you might want to change out the pump. If they don't, you're ok as you are. Many folks use these pumps for street applications and do just fine. I don't recommend using them, but that's in the case of someone wanting advice on how to build an engine. Yours is already DONE. Also, if I were you and with this pump installed, I would use oil of no heavier weight than 10W-30.

Certainly, the pump won't do any damage to the engine.

[Mike Barnard Sr No 36249]

Re: Oil Pressure -1975

Thanks Joe. I appreciate the feed back. I replaced the sending unit when I first started the motor and noticed the high reading and it checked the same.
I agree with you that the high volume pump probably isn't necessary. I may change it out to a standard pump just for piece of mind.

[kelly theaker]

Re: Oil Pressure -1975

i do not understand why Joe states that no heavier weight than 10-30 be used could you expand on the reason please, also i have heard that the high oil pressure is ok , it has been explained to me that it eats up horsepower, is this correct.

[Joe L.]

Re: Oil Pressure -1975

kelly-----

With most modern engines, including modern rebuilds of older engines, 10W-30 is about right under any circumstances. However, if one has a high volume/high pressure oil pump you definitely don't want to exacerbate the high oil pressure by using a heavier weight oil than is necessary.

With my "ZL-1", I'll be using 10W-30 or, possibly, 5W-30. Definitely.

[Patrick H.]

Re: Oil Pressure -1975

In addition, you may find that as the motor breaks in, the pressure "settles down" to a more reasonable level.

Patrick

[KEN BUTCHER]

Re: Oil Pressure -1975

Hi Mike, the Z/28 motors (LT-1,L-82) if I'm not mistaken had a diffrent pressure relief spring which produced higher pressure, which I think was about 60lbs at 2000 RPM. The stock 350 motor is about 35 to 40lbs at 2000 RPM. But myself I would like to know what kind of oil pump it is because 70lbs of pressure I think is a little high, and high volume seems to be perfurred over high pressure by race engine builders.

Just my two cents worth,think about it.
Ken.

[Duke W.]

Re: Oil Pressure -1975

"High volume" oil pumps are a hot rod myth. They are totally unnecessary! The higher the volume and pressure, the more power it takes to run the pump.

Chevrolet built at least 25 million SBs, many of which were thrashed mercilessly with the standard volume pump and a 40-45 psi relief spring.

Yes, they did install a 55-60 psi spring in the standard volume pump in SHP/FI engines beginning in late '63 and used the higher pressure on later mechanical lifter engines, but the "low pressure" spring never caused a problem in my 327/340, and it saw plenty of "heavy duty" service including race track hot lapping.

No street SB needs a "high volume" pump, or more than 40-45 psi pressure.

Now, if you build an 8000 rev racing SB with lose bearing clearances, which offer less restriction to oil flow, a "high volume" pump may be necessary to maintain the 70-80 psi desired oil pressure at peak revs, but this is obviously a VERY different application from any street engine.

BTW, the same argument applies to "high volume" water pumps. Most production engine water pumps are set up to provide more flow than is necessary for engine cooling in order to get good flow through the heater core at idle. For a high rev racing engine, flow, and the parasitic power loss associated with the water pump should be reduced by either underdriving the water pump, or installing a "low flow" impeller. A typical production water pump is likely to cavitate at 8000 plus revs.

Duke

[Jack H.]

AGREE, with Pat!

There are probably two variables in this equation: the specific oil pump used as well as the internal tolerances that were held in the engine build... Machinests/mechanics used to working on race cars typically have a pride factor that transcends typical factory production norms for engine component tolerance and internal/external balance.

When these tight 'printed' engines are first fired and driven, they can exhibit higher than normal oil pressure (even after warm up) for the break-in period. I wouldn't be surprised if your oil pressure starts to fall to more 'normal' ranges after you clock 500 or so miles on the engine...IF it was highly 'printed' when assembled.

[Mike Barnard Sr No 36249]

Re: Oil Pressure -1975

Hi Ken
According to the itemized bill I received the pump is a Melling. I checked with Summit Racing product's and was told by a rep. that the model no. I had was rated for 70 lbs. and should not be installed in a motor that had over 50,000 miles on the clock.