Chevyguy04

I have a 427 big block and while at idle about 600-700rpm, the oil pressure drops below 25 psi, almost around 15 psi. Is this normal?? Also what should it be when the motor is up around 3000 rpm?

1 FMF

iTrader: (1)

yes, at hot idle it is not abnormal, it depends on what viscosity oil you are running and what the oil temp is, along with what the bearing clearances are. If you are running a 5w-30 synthetic then it is normal.
up at 3000 rpm you should be hitting on average 40 psi, again it will depend largely on oil temperature, if the motor is cold you may see much higher pressure, if it is hot then it will be consistently lower. And the max pressure is dependent on the oil pump bypass valve, most are around 70-80 psi, meaning you'll never see more than that at your oil pressure gauge.

but from a < 20psi at < 800 rpm, if you idle up to 1500 rpm or better and oil pressure immediately responds then it's not a problem. It's when it takes upwards of 2000 rpm to just get to around 30 psi that you either have a stuck open bypass valve in the pump or you have a clearance problem somewhere.

ZONES89RS

iTrader: (25)

Yep, with higher mileage motors this happens with chevys. I would up the oil weight. If it is not already been done.

Chevyguy04

Thanks for the help, I'll have to check what the pressure is when it is cold. The pressure rises right with the rpms so there isnt a problem there.

The motor was rebuilt last summer and only has 460 miles, so its not an old motor. The engine shop that did the bottom end for me said it was the best fitting motors they have done in a while.

ZONES89RS

iTrader: (25)

Either someone did not check the rod and main bearing clearance or it might have a spun bearing.

1 FMF

iTrader: (1)

that's funny, a shop that rebuilt a motor for me a couple years ago said the same thing.

they all say that

93Z2871805

iTrader: (5)

Well, acceptable oil pressure for gen V/VI big blocks is 8 psi at idle. But they use priority main oiling. However mark IV don't so it'll be a little higher. What was the previous pressure before it dropped? Did you change the filter from break-in? Because you're supposed to change the filter about 500 miles after a build to clear out all the moly and other crap. Also what kind of oil are you using? The oil could be breaking down due to break-in heat cycles.

slow95z

iTrader: (33)

too much clearance on the rod or main bearings or worn cam bearings. they may not have replaced the cam bearings and that will definitely show low oil pressure even though the crank will be getting enough oil.