Ok sorry if this will be long but I really need to get this figured out. I have a fresh 383 installed the whole time its been running its had low oil pressure around 40psi at start and around 20psi when hot. i have replaced the pump, pan, and pressure sending unit.i have pulled the timing chain cover and checked to make sure galley plugs are installed and puled the intaketo make sure the drive gear is properly seated. When i pulled the pan I removed all the main caps and they were all fine and also checked to make sure the ball bearing was installed in the number 5 main cap. So at this point i assumed everything was fine and that the bearing clearances must be on the loose side. However when i rev up the motor it vibrates at about 1600rpm and doesn't run very smoothly when there is a load on it in drive. The pcm has been programmed for a similar setup on a different motor so I wouldnt think the settings would be that far off. Should i go ahead and get the dyno tuned and see if things start getting better....?

 

1st, 20 psi is not low at all, not even close.2nd what is the ball bearing under the #5 cyl? and also check the flywheel for the palance plate still attached.if your 383 is internaly balanced(most now days are) then they might have left the plate on your flywheel.

 

yup you are correct I just realized that I did not remove the weight!! secondly 20 psi with 20w50 and a high pressure pump doesnt seem like much to me. and the ball I was referring to is the galley ball the routes the oil to the filter in the main cap.

 

My 383 is running on an engine stand right now and with a gauge that only goes to 60psi, it bounces the peg off the 60psi mark...

20psi is not horribly low for a hot engine, but it does seem down a tad for a high volume pump and thick oil.. Does it go up significantly when you accelerate?

 

when i rev it it goes up quickly to about 40 then it stays around there...i havent revved it over 4k tho because of the vibration

 

20 PSI is not low at all and removing the weight should solve your balance/vibration issues. Do that first and then give it a shot again. As long as you have pressure you should be fine.

 

AHHH stupid weights....or no weights. I had the same problem, except vice versa, I had no weight but need it. Good luck, hope its just the flexplate problem.

 

20psi on a fresh rebuild sounds low!!!! especially with 20w50 oil! if the galley plugs are in, the ball bearing under 5cap is there, you installed a new pump (question... is it the high volume pump? don't recal any "high Pressure pumps" ) a new pan would have nothing to due with pressure.
After all this one thing comes to mind is that the tolerances in the bearings are too loose and not very tight. This is not necesarily a bad thing allot of racers want the "loose" tolerances for many reasons, but for street the tighter tolerances help the motor last longer.

 

Yea the first pump was a melling 55 with gm "white" spring for high pressure used with a stock pan, the second might be moroso or something like that with a jegs pan and pickup. the pump is high pressure and volume. I replaced the pan because I was concerned about pickup tube to pan clearance and also b/c I was goin with a high volume the second time around.

 

I now remember the spring deal with the pump now... and definetly a good reason to replace the pan. still shouldn't be a concern with the low pressure your having. I'd check the bearing tolerances everything else seems like its in line to have better pressure.