I assume they are for fuel efficiency, and helping to vaporize fuel that has not made the turn into the intake runner.

Thinking of trying it on a 1bbl intake as I convert it to a parallel 2bbl intake.

Any thoughts, reactions, and suggestions welcome.

I think it's meant to trap liquid fuel until the heat of the manifold can vaporize it. Stock manifolds are bond to the exhaust system and already pretty hot, but some of the aftermarket designs have no provision to bolt to the exhaust heat riser. So I'm not sure I would bother adding one unless you're using headers.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

Most aftermarket manifolds are cast aluminum. I'm thinking they might be strengthening ribs possibly to help prevent cracks?

I have been wondering on how to improve the factory intake manifold since reading DD's observations-experience about cylinders 2 and 5 being lean when compared to cylinders 1 and 6.

viewtopic.php?f=19&t=65856&hilit=87+octane&start=15

To even out the fuel at each cylinder the easiest way is to Install multi port fuel injection.
With a MS ecu and probably other aftermarket ecu’s one can make adjustments to each injectors dead time / on time to equalize the cylinders.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Often, the most effective way to do this with a carb is to cut grooves in the manifold floor. Use these as channels perpendicular to cylinders that run rich, or pointing down the runner for cylinders that run lean. These guide liquid fuel towards or away from cylinders.

You'll also want to keep tabs on the individual cylinders - plug reading if on a budget, individual EGT probes if you are making a max effort race build.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

Thanks for the suggestion Matt. I will give it a try.