On the old cars yes, they work. Phonelic (sp?) spacers were great as well. When the carb spacers or TB spacers were installed on the older units, that had them sitting on top of the manifold, with the air flow shooting down to a common chamber, then the spacers acted like a tunnel ram, increasing velocity of the charge. That would enable the cylinders to fill up a bit more with the increased speed of the charge entering the chamber.

But with the current stuff, not gonna happen.