195.6 OHV exhaust manifold and ports

This engine was not designed for high performance; it was designed for driver convenience and comfort, and one aspect of that is fast warmup. The exhaust ports are siamesed, and 1-2 and 5-6 are not too bad, square and straight out the block. 3-4 however is odd. It has a very large chamber in the roof that heats the bottom of the carburetor. Clearly it causes a lot of turbulence and as a side effect, heats up the head bolt wells rather nicely.

So I'm blocking it in with steel so that the port dimensions and direciton match the others. It turns out to not be too hard to do. Working from fitted cardboard templates I files and ground 3/16" steel to fit smoothly to the roof and walls.

The 3-4 manifold port is likewise shaped, so I've made the wall plugs extend into the manifold. This might mean that the manifold cannot be installed on the head while the head is on the engine in the car, but that's not fatal.

The port plug is in three pieces (two shown here, I ran out of steel) and will be welded to each other in situ; it will not be welded to the casting. It will be held in the port by it's shape. I will research whether furnace cement can be used to fill the voids between the plug and the head casting. I'm not worried about it breaking up into pieces, it would just end up in the muffler and do no harm. THe cement would hopefully prevent gases infiltrating the voids and cooking the metal, and act as heat insulation.

Here's the view from the flange, of the upside down head. That's the cardboard template and two pieces of the port plug box roughed out.

Below are pics of the unmolested port. The frst two are the 5-6 port; 1-2 is identical. The others are the center, 3-4 port. The head is upside down here; the ruler is pushing "up" into the roof. It's a very deep pocket up to the floor of the intake trough, under the carb.

Below is the port roughly boxed in to the same dimensions of the other ports.

It's hard to visualize, but the port box walls extend into the manifold; the manifold narrows about 1.5" in to the same diameter as the other ports. The floor and roof are already the same as the other ports.