I noticed the 84 TA power bulge hood had a grill in the scoop opening but on the 91 Formula/TA's it had a blacked closed panel. Were the grills used only on the pre 91/92 Birds or were they availabe on those aswell?

 

Since nobody has answered, I'm guessing it has to do with carbureted vs. TPI fuel injected. The only reason to have an opening is to let air into the air cleaner. TPI Fuel injected cars don't pull air off the cowl. I would assume the opening phased out around the same time TPI was introduced.

 

You can remove the black plate on the later model cars. 4 bolts and it's out. My guess is with 89formula3 though. That, or they wanted to see how well the open scoop did on the third generation, due to the "shaker hood"s success on the second generation cars.

 

That's basically correct. The bulge was functional on many cars from '82-'84. In those years, the optional "performance" engines were either carbureted or CFI(air entered in the same manner as for carbs).

There was an air box mounted on the underside of the bulge that sealed to the carburetor when the hood was closed. And that air box had a "flap" that opened under heavy throttle to allow additional air to enter directly into the carb. That flap was right behind the grille.

The hood wasn't used at all in '85-'86. Then when the hood was re-released in 1987 on the Formula, the "performance" engine option was TPI, which didn't require such an air intake set-up. So since there was no longer a need for a direct source of air entering through the bulge, the opening was simply blocked off completely.

I dunno if GM ever considered it, but when the TBI engine came out in 1988, the hood could've been made functional again(like it was for the earlier CFI engines), or, for that matter, it could've been made functional on the 1987 LG4, too(like the earlier carbs). And since those were the base engines for Formulas, it might've given them a slight performance "boost" over base birds with those same engines. But since those were the base engines anyway, they prolly figured there was no need for it.

 

Just wanted to make sure that the 91/92 came with the black plate instead of the mini grill.