oil pressure

[2old2fast]

Back in the 60's ,alot of us use to use the front oil galley port on a sbc to hook up the oil pressure gauge instead of the rear. I'm wondering if it makes any difference i.e. are thier pro's and cons? anybody have a thought on this?


thanks, dave

 

[Ted Brown]

Should be the same oil pressure at either end, the trick is to use a 1/4" ID line to the gauge, lets you see even a flicker in pressure change, same for the vacuum gauge...A lot of guys think high oil pressure is what they need, but all that is needed is 30 lbs at speed, maybe 7 at idle... for a stock or a built engine...

 

[Screaming Metal]

Should be the same oil pressure at either end, the trick is to use a 1/4" ID line to the gauge, lets you see even a flicker in pressure change, same for the vacuum gauge...A lot of guys think high oil pressure is what they need, but all that is needed is 30 lbs at speed, maybe 7 at idle... for a stock or a built engine...

Teds exactly right! :thumb: SBC only takes 7 psi at idle. Run too much pressure and you run the risk of twisting a shaft off or have spark scatter at high rpms. Pressure gauge at either end is good. I used to screw in a 90 have a short line and a bracket right by the valvecover to check pressure while tuning....

 

[ellis8500]

A good estimate of required oil pressure of SBF's is 10 psi per 1000 rpm. So at idle, about 10 psi. At 3000 rpm, 30 psi is OK. My rebuilt engine, which only has a few hours of engine test stand time holds higher pressures now. After proper under-load run-in, I suspect it will be somewhat lower. At startup with 70 degree oil, it idles at about 60 psi. Pressure comes down during heatup.

 

[Ted Brown]

60 lbs, sounds like too much oil bypass spring tension to me... ?

 

[putz]

When putting in your gauge first thing you do is throw away the plastic line it comes with and go get copper line I have seen to many plastigc lines either melted or rubbed through.

 

[Mike]

As Ted mentioned, oil pressure should be the same, front and rear. If it is not, you have some issues.

Personally, I prefer checking pressure at a point closest to the oil pump. That way, you're seeing the same thing the engine is seeing. If you read pressure at the front, the oil pump can expire before you see the drop at the front of the motor.

+1 on running large lines to gauges. They will be more sensitive to changes. And unless you live on a washboard, dirt road, leave liquid-filled gauges to the dirt track racers.

Extremely high pressure figures can result from tight clearances, as well. Checking bearing clearances can be one of the most time-consuming steps of engine assembly. But is can also be the step that adds thousands of miles of life to your engine. If you think a crank has been ground .010" and you think you are using a bearing for that size, you really don't know a damn thing. You're trusting the machinist to have had a good day, as well as everyone on the bearing manufacturer's assembly line. Check those clearances and check them on each journal, so you know what you have for clearances. Yes, it can be a tremendous PITA to remove a crank and polish a couple tenths off one journal, but it makes it right. Making it right is what lets it live, so don't neglect this procedure.

 

[RPM]

For street use, not racing use. I would recommend using and electric gauge. No hot oil in the passengers compartment and the electric gauge with change much quicker than a mechanical if you lose pressure.

 

[Lee_in_KC]

I've never checked this on an automotive motor, but on an airplane motor, specifically a Lycoming IO-360, there IS a difference in readings between the front tap and the rear tap. Here is my experience... I had a new (in 2003) electronic engine monitor installed on my airplane. I noticed afterward there was a difference in oil pressure readings between the electronic monitor and the the original oil pressure gauge, which was a mechanical gauge using a copper capillary tube. I asked the mechanic who installed the monitor about it, and he said he had to use the front tap for the oil pressure sender for the monitor, because the rear tap was already taken up by the original mechanical gauge tube and there wasn't room to use a tee (translation: "I was too lazy to re-work the rear tap set-up."). I asked why the difference in pressures, and he said as the oil moves through the galleys from the rear of the engine to the front, it loses pressure. He said it was "perfectly normal." Intuitively, that made sense to me, but I called Lycoming just to make sure. They said, "yep, that's normal." At take-off power (2,700 rpm), the rear tap was reading 70 psi, and the front tap was reading 55 psi.

I'm just sayin'...

 

[sstock]

I've never checked this on an automotive motor, but on an airplane motor, specifically a Lycoming IO-360, there IS a difference in readings between the front tap and the rear tap. Here is my experience... I had a new (in 2003) electronic engine monitor installed on my airplane. I noticed afterward there was a difference in oil pressure readings between the electronic monitor and the the original oil pressure gauge, which was a mechanical gauge using a copper capillary tube. I asked the mechanic who installed the monitor about it, and he said he had to use the front tap for the oil pressure sender for the monitor, because the rear tap was already taken up by the original mechanical gauge tube and there wasn't room to use a tee (translation: "I was too lazy to re-work the rear tap set-up."). I asked why the difference in pressures, and he said as the oil moves through the galleys from the rear of the engine to the front, it loses pressure. He said it was "perfectly normal." Intuitively, that made sense to me, but I called Lycoming just to make sure. They said, "yep, that's normal." At take-off power (2,700 rpm), the rear tap was reading 70 psi, and the front tap was reading 55 psi.

I'm just sayin'...

Agree, in any hydraulic system there is friction loss from the fluid moving through its pipe, changes in fluid temperature,viscosity, pipe size,flow velocity and length of pipe all influence pressure loss through the system from pump discharge through the system to pump inlet.

 

[Screaming Metal]

From our Beloved MIKE....

Personally, I prefer checking pressure at a point closest to the oil pump. That way, you're seeing the same thing the engine is seeing. If you read pressure at the front, the oil pump can expire before you see the drop at the front of the motor.... :thumb:

 

[Ted Brown]

I will agree to that, the closer to the pump, is always better, they is always a better way, no matter what it is... I truly believe this...

 

[ellis8500]

Ted,

The oil pressure will be higher when the engine is cold. 60 psi is OK and would be the right amount when engine is turning 6000 rpm. When the engine gets hot it drops down to about 15 psi at idle. When I rebuilt the engine all crank journals measured stock size. Seven bores measured stock, One was 0.004 oversize near the top. There were no ridges at the top of the bores. Block only needed a cleaning and a light brush hone on the cyclinders. The engine came out of an F150 pickup. I replaced the fuel injection system with an Edelbrock 289 Perfomer intake and a Summit 600 CFM carb. Also a higher performance cam replaced the truck cam. So the inside is "Brand New Tight" right now. I think I've run about 5 gallons of gas through it on a test stand that I built. I forgot to mention that the engine had 180,xxx miles on it when I got it. Truck engines can make great starts for a rebuild project since they often use heavier duty parts and are usually run at lower rpm's. It's the higher rpm's that wear out an engine.

 

[lkeuten]

From our Beloved MIKE....

Personally, I prefer checking pressure at a point closest to the oil pump. That way, you're seeing the same thing the engine is seeing. If you read pressure at the front, the oil pump can expire before you see the drop at the front of the motor.... :thumb:

Out here in the big cornfield between Iowa and Colorado we use shut down gauges on irrigation engines. They are set up to shut the engine down if the temp gets to high or the oil pressure gets to low. Always take the oil pressure on these as close to the pump as possible and give yourself a little breathing room off of zero oil pressure.

 

[Gerry]

Out here in the big cornfield between Iowa and Colorado we use shut down gauges on irrigation engines. They are set up to shut the engine down if the temp gets to high or the oil pressure gets to low. Always take the oil pressure on these as close to the pump as possible and give yourself a little breathing room off of zero oil pressure.

OK
I may be completely out of the ball park here, but I cat remember the last time I had an oil pressure problem on a mild engine. Never had an oil pump give up on me and that includes some very nervous 4 bangers.
Gerry

 

[2old2fast]

IIRC, the reasoning behind reading off the front was that you saw what the crank and rods saw ,not what it was before it went through the valvetrain,if this makes any sense??!


dave