What is good oil pressure on a sbc 350 I am reading 10psi at idle and 55psi at cruising speed.?

In general, the engine should be able to maintain oil pressure at an idle. When the engine speed drops to an idle the oil pump naturally moves less oil, but there is nothing wrong with the pump, it's doing it's job perfectly. When the engine is at cruising speed the pump is turning faster and moving more oil. A potential exists for the pump to move so much oil that an overpressure condition would exist, destroying the pump, the drive mechanism or potentially one of the bearings.

To prevent that all engines are equipped with an oil pressure limiting mechanism. It's a simple spring loaded piston that is pushed out of the way when the pressure exceeds a specific setpoint, allowing extra oil to escape back to the crankcase.

Engines are designed so that the oil pump will maintain pressure at all speeds. Technically, the rod bearings and main bearings never actually touch the crankshaft; instead they ride on a film of pressurized oil. When the engine first starts the pressure has not yet built up and the bearings actually touch the crankshaft. Not much wear occurs but over time the babbit material that is on the bearing surface touches the crankshaft often enough that the babbit wears away, opening up the space between the bearing and the crankshaft. The larger space allows oil to leak past at a higher rate often overwhelming the pumps ability to keep up. That's when the oil pressure drops.

But don't worry, it isn't necessarily a TERRIBLE thing, it just means the engine is getting older.

The bypass pressure is the highest pressure that you see on the gauge when the engine is at cruising speed. That's when the pressure regulator is in control, that's how you like it. You don't want to "lug" the engine (put it under load) when there is low oil pressure as that can cause more bearing wear.

So...

Switch to a higher "viscosity" oil. That will be an oil with higher numbers. Whatever you've been using in the past, just go to the next number UP.

If you've been using 10W30, try a 15W40 or whatever works for your engine. You should see an immediate change in the oil pressure and the gauge SHOULD stay at or near the bypass pressure.