With both these engines, the first thing to do is check the oil pressure with an alternative, known-good gauge.
If the results are similar, then both engines may have problems with oil pressure.
Not a lot of addtional information was given.
What kind of oil is used? If it's lower than a 10W30, use a higher viscosity oil.
What is the mileage since the last overhaul?
Have either of these engines had any modifications that affect the oiling system?
Without the answers to those questions, it's awfully difficult to diagnose by Internet, however, if the oil pressure is checked with a known-good gauge and is less than 20 psi hot at idle, you could pull the pan and check the oil pump.
Another thing to look for is an internal oil leak--perhaps a front oil galley plug that's fallen out or a leak around the dist. body.
If you drop the pan find the oil pump and pick-up are ok and there are no internal leaks, try replacing the oil pump pressure relief valve (it's in the oil pump bottom plate behind a roll pin) with the "high-performance" spring, GM PN 384891. In an engine with an oiling system that is working right, using SAE30 oil, this usually makes 60-70 psi, hot, oil pressure at mid-range or higher rpms. Generally, the rule is 10 psi hit oil pressure for every 1000 usable rpm. So...if you're engine has an upper usable rpm limit of about 5500 rpm you want at least 50 psi.
Also, on "high-volume" oil pumps. Contarary to what's posted previously in this thread, there are very, very few SBV8s that need high volume pumps. This is especially true of stock or even most modified engines using production blocks. In most cases high-volume pumps do nothing but add parasitic power loss and pump too much oil into the top of the engine. Bottom line: unless you are building a very high rpm race engine (such as for NASCAR or drag racing) don't use them.
