How high is too high? I'm seeing about 55 psi at idle and about 75 psi at 3k rpm, is this too high? This is on a new 383 sbc.
Any help would be appriciated, Steve

 

What weight oil are you using? Is this with the factory guage - or have you verified this with a mechanical?

I would typically look for around 35psi warm idle, 70psi high rpm. If you are at the track, the idle psi could drop to 20lbs after some hot laps and you are still good. 55 at idle is high, do you have a build sheet for the motor with the main and rod bearing clearances listed?

 

I am using 10w30 oil and this pressure reading is with an electric Autometer gauge.
The bearing clearances on the mains and rods were at the minimum recommended size. I think the mains were .002 and the rods were .004 ( don't quote that, but I do remember they were tight). My buddy did all the measurements on the motor so I just let him be and do his thing. I also used a Melling high volume pump. What would be the down side to higher than normal pressures?
Thanks, Steve

 

.002" is tight.

 

If you deem that unacceptable the easy way to get less pressure is just to go in and change the pump spring to something lighter to relieve pressure at whatever you want.

 

What made you think that .002 was okay? (I'm not trying to jump on you, would like to know where you got the info.)

A stock SBC with a crank journal of 2.45" should have .0025" clearance. For performance applications you need to run it looser .003".

 

Perhpas you would be best served by switching to a full synthetic in a 0w30 weight? Seeing as how your clearances are fairly tight.

 

You can run it at .020 if you feel like that is needed.... It will make the oil pressure high though.

Bret

 

".020" = serious hemmorhage

Bret, you aren't very decimally-inclined are you?

Couldn't help it man.... I couldn't pass that one up.

-Mindgame

 

:scratching head: I think there is more to it than that, MG. Afterall, Brett did state, " It will make the oil pressure high though." If clearance (for whatever he's referring to) was too large, why would he state it would make the pressure HIGH? Doesn't it sound contradictory?

 

I'm pretty sure that was a typo

Usually you will run the mains at .0025-.003" and the rods at .002-.0025 for a performance motor, the rods should be tighter than the mains, because the mains feed the rods.

Also its calculated by journal diameter (.0075"-.001" x Diameter)
So on a SBC the mains are 2.45" that would mean slightly over .0025 main clearance. ( for a stocker, performance add .0005")

 

lol yeah I think in tenths... (ten thousands) with clearances so I miss a zero here and there in typing....

 

"Decilexiphobia"--a fear of misplacing decimal points and not remembering where they belong. Very common among Congressmen and some machinists/engineers.

Some of us "think in thousandths" as in boring a cylinder "30" over. That's really .030 but we mentally move the decimal point 3 places to the right. So fitting a piston pin with a "5/10ths" clearance is .0005, not .5. If you regularly work in portions of a thousandth, you might "think in tenths" which is actually "think in ten-thousandths" or .0001, so the piston pin would have "5", not .5. It can get confusing, and expensive when someone specifies a tolerance as .0002 when they meant .002.

My $.02....or is that $20?

 

LOL - I can't remeber how many times I have mentally moved the decimal point over and totally confused people when it makes total sense to me.

 

Bret,
Thanks for taking that for what it was... a crude attempt at some humor.

Arnie, *shakes head*
What am I going to do with you?

I'm having some issues with moles right now... I've set traps, flushed their tunnels and mounds with water and the little buggers keep popping up somewhere else. What I need is a guy like you who could make something useful of these mounds..... like maybe make some mountains out of them.
I've always wanted a 1/2 or even 1/4 scale replica of Mount Rushmore. So what do ya say arnie? You up for a challenge?

Disclaimer: The mole part is real... unfortunately. The rest was an attempt to poke at arnie a little.



-Mindgame