To De-Smog or not to De-Smog...
E.G.R. stands for exhaust gas recirculation valve it is used to reduce the formation of NOx by introducing a small amount of exhaust into the combustion chamber
Correct.
it is connected to both the intake and exhaust
Dude, don't guess at things you don't know. Go use your eyes. Go
look at two dozen different slant-6 exhaust manifolds. There is
no connection for an EGR valve on any slant-6 exhaust manifold. Right from the very start in 1960, the slant-6 intake and exhaust manifolds bolt together at the center to provide intake manifold heating (the hot spot) for proper vaporization of fuel: exhaust passes across the underside of the intake manifold floor, and that's how the intake is heated. When valve-controlled EGR was introduced in '73, an EGR mounting pad and two new passages were added to the
intake manifold. One passage goes from the underside of the
intake manifold floor to the EGR valve mounting pad. The other passage goes from the EGR valve mounting pad to the inside of the
intake manifold. The EGR valve, mounted on the
intake manifold, controls the flow of exhaust from the underside to the inside of the
intake manifold. The exhaust manifold does not know or care whether an EGR-equipped
intake manifold is bolted on. Deleting EGR from a slant-6 does not involve any mods to the exhaust manifold because (everybody, all together now!)
there is no such thing as a slant-6 exhaust manifold with EGR provisions.
(the '72 California slant-6s had a very primitive EGR "system" consisting of nothing but a hole in the intake floor, connecting the underside to the inside so exhaust entered the intake tract whenever the engine was running. Engines so equipped were a bitсh to start, idled high and poorly, and got awful gas mileage.)
