Hey everyone,

Put a brand new stroker 383 motor in my car this spring. Broke it in and put about 1000 miles on it. It has a hv pump with a stock pan(came from the builder that way). Engine runs super strong with no noises as far as I can tell. When I start it up cold, the pressure goes to 45-50 . But after it warms up after driving it for a while it dips just below 20. When I am cruising on the highway at part throttle it is at 45-50 and if I let off the gas while coasting on the highway it will go to 35-40. But as soon as I slow down and stop at a light, it drops to just below 20. If I put it in park it will go to 22-25. Is this normal? or a problem? It is a brand new motor and I have changed the oil and filter after the initial break in. I guess I am most worried about bearing failure in the engine, but since it is brand new is this likely? I ran a couple of spirited bursts on the side roads but no drag racing or heavy red line racing has been done. Just want to know the best step by step course to take from this point on . Also running 10w-40 for oil. If it is bearings what should I look for if I have to drop the pan? Sorry for all the info but figure the more info you have the better chance you may be able to help. I have no experience in engine building, or diagnosing engine problems so any help on what exactly to look for and locations would be very helpful. Thanks in advance!!!!

10 psi per 1000 RPM is fine.

Could be your gauge is off at the low end. I'm using a stock GM center console pressure gauge in my 69 350. Cold startup at idle is 55 to 60 psi, running down the highway at 2500 rpm hot is 45 to 50 psi, idle (700 RPM) cold is 20 to 25 psi, now for the scary part. Idle hot is less than 10 psi at 650 to 700, jumps right up to 20 at 1000 rpm. Engine has done this since new (1985). Put about 40K miles on it, mostly just cruising, with some random thrashing added in. Never had any issues with the engine. Just rebuilt the whole engine, new pistons, ring, bearings, HV/HP oil pump etc. mainly to up my HP alittle, figuring as a side benfit it would resolve the oil pressure issue. All the old bearings removed looked like they were new, not a single gouge or other mark in them. When I was done the oil pressures are exactly the same as before. So I'm blaming it on the gauge. Maybe one day I'll buy a new gauge to see if its off.

From your description, your oil pressure is fine. Enjoy driving the car. 10 psi per 1000 rpm is the correct benchmark.

Originally posted by mark67ss:
Hey everyone,

Put a brand new stroker 383 motor in my car this spring. Broke it in and put about 1000 miles on it. It has a hv pump with a stock pan(came from the builder that way). Engine runs super strong with no noises as far as I can tell. When I start it up cold, the pressure goes to 45-50 . But after it warms up after driving it for a while it dips just below 20. When I am cruising on the highway at part throttle it is at 45-50 and if I let off the gas while coasting on the highway it will go to 35-40. But as soon as I slow down and stop at a light, it drops to just below 20. If I put it in park it will go to 22-25. Is this normal? or a problem? It is a brand new motor and I have changed the oil and filter after the initial break in. I guess I am most worried about bearing failure in the engine, but since it is brand new is this likely? I ran a couple of spirited bursts on the side roads but no drag racing or heavy red line racing has been done. Just want to know the best step by step course to take from this point on . Also running 10w-40 for oil. If it is bearings what should I look for if I have to drop the pan? Sorry for all the info but figure the more info you have the better chance you may be able to help. I have no experience in engine building, or diagnosing engine problems so any help on what exactly to look for and locations would be very helpful. Thanks in advance!!!! Sounds right on to me!!

Are you sure you don't have a stock pump and not a HV? Your oil pressure is exactly what a stock pump would do but a HV. pump would almost double the pressure at every RPM.

Hello,

Correct me if I am wrong but

Hello,

Correct me if Im wrong but I thought a HV pump means high volume. I dont think that it has an effect on pressure just the volume of oil it moves. I think they sell high pressure pumps as well that get you more pressure but move the same amount of oil. Maybe I need a higher pressure pump with the stock pan I have. Any thoughts or should I leave well enough alone.

hey Mark,
I was just about to post this same question myself when I spoted your post. My 67 does the same thing. Its a newly rebuilt motor with about 7K on it.. I am running an autometer electric guage , are you running an electric or mechanical? I always have at least 10 psi per 1000 rpm so I think im alright. so it runs anywhere from about 20 psi to 60 when warmed up. Freeway driving ill run a stout 51 psi but at idel she drops to 20.

To put the question out there to you others with insightfull knowledge. Is there iany difference in the accuracy in an electric guage to a mechanical one. ???? I prefer electric to mechanical as they are so much easer to plumb :D

Hey Dragon,

Know what you mean. Glad to see I am not the only one concerned with this problem. I get the same exact thing. Almost freaky the way you describe it. Anyways, I run a mechanical gauge. I dont like electric because of the gremlin factor. Me an electronics dont really mix too well so I try to use mechanical where ever I can. I have had to replace a sending unit twice on my tranny gauge,which is electric and a pain in the butt.

I think Oger hit the nail on the head. Oil pressure is fine, nothing to worry about, BUT the pressure is more consistent with what I would expect from a stock oil pump.

As for the pressure vs. high volume question. Volume and resistance to flow determine pressure. They are directly related.

If volume and resistance in an engine all remain the same pressure will also remain the same. If you increase only volume pressure will increase. If volume remains the same and resistance to flow increases pressure will increase. If the oil thins when it gets hot resistance to flow decreases (thinner oil flows easier) so oil pressure decreases too. If you broke a lifter and it popped out of the bore resistance to oil flow goes way down and so does oil pressure. If you plug an oil galley resistance to flow goes up and so does oil pressure.

There is no such thing as a high pressure pump, only high volume pumps and standard volume pumps. You can change the internal relief set point by using a heavier spring which raises the pressure at which the bypass lifts, but that does not increase your oil pressure --- it only raises the oil pressure limit.

Just resolved my oil pressure problem. I had the cover of my console gauge housing so I bent the oil gauge peg on the 0 pressure side down with the engine off. The needle went to the left off the scale about 3/8". So I reset it to read 0 with the engine off, and the pin bent flat. After starting and stopping the car a couple of times to see where the needle returned to I straightened the pin back up. Now I've got 30 to 35 PSI hot at idle (700 rpm). Haven't driven it anywhere to see what it goes up to at speed. Knew I didn't really have a problem because the engine never would have survived for the past 18 years with the low idle pressure the guage indicated

Back in 85 when the gauge was replaced, you had to buy the Black faced gauge from a Nova, and swap the black faceplate for a silver one. Guess I didn't get the needle back on right when I swapped the faceplates.

Edit:
75 psi at 2500 RPM now. Much happier when looking at the gauge now.

[ 06-30-2003, 05:26 AM: Message edited by: Mark C ]

I don't think you solved your "oil pressure problem"...I think you wrecked your gauge!! They aren't calibrated for 0 psi...they're calibrated for 30 psi...or 50 psi...something in the normal operating range. That pin is there for a reason - to keep it from falling off-scale at rest. If it was necessarily designed to sit at zero at rest, there would be no reason to PUT a pin there. All you've done is UNCALIBRATED your gauge!! You've changed what the gauge reads...but don't necessarily have any idea what the pressure is. I'd have your pressure checked at a shop with a separate gauge and make sure you're reading the right pressure.

I wouldn't recommend this as a popular oil pressure problem fix!!!

I agree with Eric68, your point is spoken well, as always.

I also agree with Huck for other reasons in stated question.

I am an Instrumentation Engineer, so my opinion falls on said education.

Most of all pressure gauge designs are CAL'd in a known given operating range/environment, mechanical or electric. The electric version needs voltage present to work, because it works off of the potential resistance of an electrical transducer (the sender) and is not at zero volts when indicating zero measurement. An electric gauge, with the exception of a volt or ampmeter, has a zero point above zero volts. It is most commonly aound +1 to +3.5 volts DC and has a working range from +3.5VDC to +13VDC. An easy example of this is a fuel sender. It doesnt start at zero OHMs.......for indication. It has to start at a known/given resistance for its useable resolution of bandwidth (range of motion).

The mechanical needs pressure to operate, but doesnt require any electrical input for operation. A mechanical is zero at zero and is less effected by other electrical anomalies or intrinisic error, but its initial reading indication is calibrated to a mechanical input, IE a known value of pressure or vaccume.

Mark now that you have bent the needle and/or stop, it is out of its 'set' calibration. I wouldnt trust it for anything, except that with needle movement, you do actually have pressure. 20 PSI at idle and 50 PSI at cruise is normal with the weight of oil that you are using.

I also read the question concerning the differencces in mechanical and electrical gauges and their respective accuracy.

Dragon Most of any answer to these questions relate to the quality and manufacturer of a given product. Most of whats available on the market isnt all that bad. As for a difference between mech and elec there are more variables in the elec operation than that of the mech operation. Mechanical is pretty straight forward. It needs a mechanical force (or input) to operate and works without electrical input (most of the time, with the exception in engineering calibration). A mechanical error percentage is far less than that of an electrical; Maybe 1.5% in indicated range.......

Now as for the electrical, there are some things that can skew the accuracy not related to the gauge itself. Electrical circuits are only as good as the wires and contacts allow it to be. Even a bad ground can cause a notable error in said measurement. An electrical error percentage can be into 30%, in an indicated range from anomalies alone. But not likely. I would have to say more like 10-12%.

Hello, My name is Tom, and I am a gauge whore . I have 14+ Autometer ProComp gauges and am about to add 34 channels of data acquisition to my 67.......just to 'see' whats going on. I am a fan of mechanical gauges for multiple reasons, although, in some cases an electrical transducer is still easier to install. Its only wiring.......so most view it as most being more asthetically appealing and simple. Me, I just want accuracy without gremlins.......