The stock inlet manifold on the 4AC Corolla is an aluminum casting for a downdraft carburetor. It bolts to the exhaust manifold and actually has a section where exhaust gas is in direct contact with it to with help driveabilty under cold conditions. There are two styles of manifold that I am aware of, one for the RWD Corollas, and another for the FWD Corollas that allows for a lower hood clearance. If anyone has another type of OE manifold please submit pictures.




This is the RWD version




This the FWD version


This shows how the FWD manifold kicks down between the head and the carb. The RWD versions is pretty much straight across. I doubt that the FWD versions is as good as the RWD one with the extra bends. They are pretty much the same other than this though.

The flow path in this manifold seems to be rather tortured. The air comes in through the air cleaner, makes a 90 degree turn down into the carburetor, then goes into the manifold and then has to make another 90 degree turn cylinders 1&2 or the other way to cylinders 3&4.



Then another 90 degree turn has to be made towards the head, and then a final approximately 45 degree turn to line up with the inlet port.



When the ports are separated into single cylinders runners, the ports got to a constant 28mm diameter which seems rather small.



As stated earlier the inlet manifold is bolted to the exhaust manifold. The exhaust manifold is braced to the engine mount casting on RWD Corollas. It would probably be wise to add an inlet manifold brace if you go to headers to replace the one that was attached to the exhaust. The reason the section manifold was available to be cut up was that it was not braced and had cracked in the #1 runner right next to the head. Itseems that the lack of the brace allowed the manifold to vibrate/flop around excessively causing the crack.



This is an example a brace. You can just mount it the other end to the engine mount where the original brace mounted (unless you have an S&S header in which case you have cut that boss off so the header will fit).