My 6-71 Blower rebuild, Part 2: Milling top ribs from the case 

Certainly for the top ribs, one of them is right in the way of the carb venturis so it could cause some strange mixture distribution problems. That is why I removed mine, to give the throttle bores of the Holleys an unobstructed path into the top of the blower.

MakerCave absolutely , kinda makes sence 👍

A combination of aluminum wheel cleaner, and walnut shell blasting. Please see video #8 for details. Thanks for watching!

Yes, it might seem like that at first glance, but consider why the ribs are there in the first place. 1. When the case was originally cast, these ribs provide channels for the aluminum to more easily flow into both sides of the pattern in the core box. 2. During final machining of the casting, the ribs provide additional stability to the casting, and to help keep the boring and surfacing tools from chattering when the case is machined. It would have been extra, unnecessary work for GMC to do an additional operation on the case to remove the ribs after manufacturing is complete, so even though they are no longer needed after original assembly, the ribs are left in place. Once the blower is bolted on, the intake manifold provides a giant support surface, and the large center ribs still remain, so the case is quite stable, and there are no appreciable loads trying to "spread" the case in the areas where the casting ribs are removed. Independent of these things, hot rodders have been removing these ribs since the 1940's and the current blower manufacturers make their cases without these ribs, even for very high horsepower applications. This all confirms that the minor ribs are redundant, and can be safely removed in gasoline engine applications. Thanks for watching!