Good question. Yes, I have heard of this for some engines, but it is very rare. Never seen one. Basically the divider is on the exhaust manifold and fits into the port.

Does it really matter?

Mini engines have siamesed exhaust port, and use a 3-branch exhaust. They are circular and the way performance is improved is to use tubular exhaust with a long, larger diameter, center branch, called a LCB (long center branch) exhaust.

On some divided port heads, hot-rodders grind away the divider to make a siamesed port. For these heads the flow increase is more beneficial than the scavenging effects.

So it's not so cut and dried. The exhaust port design on the A-series is fairly good and receives very little attention.

Small-block chevy has separate center ports, but a siamesed exhaust manifold. Replacing this with tubular headers makes a huge improvement. Not so much with the A-series, as the cast manifold is already a 4-into-2 design.

The GX manifold, although cast, is a long Tri-Y design, nearly as good as a header, and certainly more durable and reliable. Racers still use tubular headers for tuneability (changing length of collector, tube diameter, etc). For a street engine ran in a variety of RPMS, and where fine tuning will NOT happen, the GX manifold is the answer.

Dividers have been sold


But never dyno tested, so no one really knows. See Do I really need a port divider? Will I get better performance or an increase in mileage?