WTF. Why do the V-6 engines have only one exhaust port per side

That's a contrived leap of logic. There are already exhaust gas passages from the combustion chamber to the ports on the outside of the head. Remember there are two exhaust valves per combustion chamber, so even the old engine design had a 6-3 merge happening in the head. Incrementally increasing it to 6-3-1 within the same head doesn't degrade reliability. It's better than a brittle cast iron exhaust manifold that can't thermally expand and flex with the engine.

 

22RE on an 1989 4Runner, cracked in the exhaust port into the coolant passage. Started pissing coolant right into the exhaust manifold. Replaced the head, 3 months later same thing!

 

Has anyone tried to polish the exhaust side of the head or increase the port size to see if there are any increases in power. Mainly curious with someone running the Magnuson supercharger.

 

The decades of work done by Toyota engineers wasn't as smart as you, I guess.

 

It isn't smart. It is a cost saving measure. It eliminates any chance of real exhaust tuning, and now limits the ability of building a hi performance n.a. engine. You could probably extrude hone the passages, depending on port thickness, but you wont be able to change the lengths. The key to horsepower lies in the engines cylinder heads. All this stuff was figured out by drag racers decades ago.

 

HP? Or forward gears ?

 

Ports. It has the power it needs for the job.