Ok, so this is what I have:

350 +.030 block
Scat Lightweight Crank
Forged rods
Hyperutectic Pistons
Total Seal Moly Rings
Oversize Bearings because of a 4 bolt conver.
Nitrous HP roller cam
Roller Rockers

Now the problem, The motor has about 400 miles on it. I first broke it in on 5w-30 found it was too thin after about 5 miles, dumped it right away and put in 10w-30 oil. At 100 miles I changed the oil again to inspect it. Then the motor sat for about 8 months, being started every so often. Swapped the motor into another vehicle, changed the oil at 225 miles and put in 10w-30 again with zinc additive.

Cold start I have 40-50 psi. I took it out on this nice 90* day and drove it around a bit (maybe hour to two) and the highest RPM it hit was about 4000 reading 40 psi. Then dropping down to idle the oil pressure dropped to 5 psi. Then after a second would jump to 20 psi still idling. The temperature at the time was 180*. I know it's not a problem in the gauge because it's mechanical and after limping it home giving the throttle a little move to change the RPM I got lifter tick. Oil is full.

Am I running too thin of an oil? If I am, what weight should I be using?

 

possibly you could be running to lightweight of oil, although I think it originally called for 5w30. Try draining the oil and using 10w40. Also, when you do that, add a quart of Lucas oil treatment. That should quiet things down.

 

When the engine was built, what were the bearing clearances set at? Were the cam bearings replaced and installed correctly??? What oil pump did you use?

IMO, 10-30 might be fine in a cruiser, but when I have any kind of a performance engine I run 20W50 Mobil 1 or Royal Purple synthetic. If you don't like synthetics, then any good 10W40 or 20W40 should work ok..

 

Oh it was so long ago I built it, I can't even remember. It was built to be a performance motor though. If memory serves me correct, the oil pump was a stock type replacement, not a high flow. Every bearing in the motor was replaced and the cam bearings were installed by the machine shop that did my work.

I'm not too sold on the synthetics yet because had a motor I tried it in and just became a weeping mess

 

Yup, takes good sealing to run synthetic oil!!! But, 5 years of circle burning and 30 years of drag racing with no bearing related engine failures pretty much sold me on the Mobil 1! Anyway, think if I were you I'd just go to a 20W40 for the summer...If you drive it in the winter (gasp!!!!, Minnesota!!!!), could probably drop back to a 10W30.

 

What are you using to check the oil pressure? The sending unit on a SBC is notorious for being off or going bad.

If you had 5 psi every lifter would be chattering.

 

i agree with the fact that the SBC sending unit is notorious for inconsistent readings... however 10w30 should be ok...

switching to a 50w oil is only a band aid for the excessive bearing clearances

the only way to solve this permanently is to take it apart and buy the proper bearings

that is if there isnt any damage

 

Could be a poor Oil Pressure Switch as well. The bad boy threaded above the oil filter.

 

autometer manual oil pressure gauge running at the port next to the distributor, no sending unit and yes every lifter WAS chattering.

I'm not thinking it's the bearings quite yet, It's a performance motor built from just a block. Everything was measured at assembly. I just think the oil is too thin at this point.

lol and HELL NO I won't drive this in the winter! I like my good cars not to rust out :P

 

okay... if you are confident in your preassure gauge... you are down to two options...

1. bad clearances... bearings/pump/lifters
2. damage...


take a look at all of the threads that are complaining about low oil preassure when the engine is at temp... they are running atleast 10w30 if not on to 10w40 some i am sure have gone to 50W you are experiencing the same symptoms as other high mileage engines... bad clearances...

i would not assume that because everything was "measured" that they didnt see a .019 clearance and say "oh damn to late now we already bought the bearings" and just throw it together...

but maybe i am wrong throw a 50w oil in and start driving it at about 600 miles you will know if it really was the bearings... the oil will start to break down and oil preassure will be back where it was with the 10w30

 

Nobody said try straight 50W.... Just for conversation I mentioned that I run 20W-50 synthetic oil in MY performance (ie racing)engines.... Maybe read the entire post next time?

 

while running a straight 50w oil is not what i had in mind... a 20w-50 oil at temp is the same thing as running a straight 50w oil...

didn't think i had to say that... maybe it is because i didn't read the thread....

but your right 20w-40 will do the same thing as a 10w-40 or a 20w-50 for the purpose of narrowing down the problem however i am willing to bet that after trying a 10w-40 the OP would move on to a 20w-50 just to be sure so why not start with the 50w and get it over with... i mean if its 90* outside do you really think a 20w-50 is going to be much different than 50w at start up?


and the OP is complaining about oil pressure at temp...