They are called "Floor Jets." The holes don't go into the crankcase, they go into the exhaust crossover - unless the manifold has rusted through. They recycle a tad of exhaust gasses back into the intake. It's called Exhaust Gas recirculation. It's the early form. It controls Nox and HC emissions.
They are a fixed constant opening. They were used for a few years, then dropped in favor of something more controllable - an external valve - called the EGR valve.
Most of the time the small orifice is worn bigger, giving too much exhaust, affecting performance too much.
Tap and plug them.
Don't use epoxy as plugs - the plugs can come loose and get under a valve, causing lots of problems.
The PCV is an entirely different system. It has a hose from the intake manifold to the crankcase or valve cover. In that hose is the PCV Valve. It sucks the fumes out of the crankcase - keeps the engine oil clean.
Then at the other end of the engine or rocker cover, it has a fresh air intake. It should allow fresh clean air into the engine. Usually it gets it's air from the air cleaner.
The idea is to have clean fresh air come in one end, sweep through the engine to gather up the fumes, then get pulled into the intake to be burned. It's not detrimental to the engine at all - in fact, it helps it stay clean and live longer.
Last edited by RRich; 07-06-2009 at 08:56 PM.