sssoooo as we all know there is a egr port that runs across the heads via the intake manifold. ive heard about blocking this off but what is the function of that port? looking for hp n economy. and what are the benefits from blocking it off?
EGR and carb heat are two different things
EGR is Exhaust Gas Recirculation, and is PURELY a result of smog laws passed in the late 60's / early 70's and all the screwball schemes car makers went through to try and "meet" the smog targets
EARLY Mopar EGR had no control valve at all. Simply, Mopar just drilled a couple of holes in the bottom of the intake, right under the carb, so that exhaust gas leaked into the intake from the crossover below (get to that in a moment)
This was a REAL poor deal, and a year or so later, they finally modified the intake and put an EGR control valve up on top of the manifold, controlled by a vacuum operated diaphragm.
NOW, CARB HEAT
is a whole different brute, and has been around since the '50's
Carb heat on a V8 works like this
In one exhaust manifold is a thermostatic operated butterfly valve, which, when cold, essentially PLUGS that exhaust outlet and FORCES exhaust gas up through the center port in the head, across through the passage in the intake, and out the other head and out the exhaust on that side.
This heats the floor of the intake, preventing carb icing (which can happen in high humidity MUCH above freezing) improving fuel vaporization, AND on newer cars with the "well type" choke, heats the choke thermostat as well.
As said above, depending on your climate, (northern, colder) you probably should leave the crossover unblocked for daily driving.
In southern, warmer climates, you can get by OK blocking it, and may be better to block in some warm climates to prevent vapor lock and other fuel boiling problems.
The irony is that some older cars that have "carboned up" often have the thing plugged up, anyhow!!
