[njsteve]

Yes. All SD455 Firebirds, whether Trans Am or Formula had the shaker. It was not due to any performance upgrade but instead was due to the fact that the EPA only certified the emmissions and drive-by noise regulations on that precise set up. GM would have had to recertify the engine package from scratch just to use the Formula fiberglass hood. If you look at the window sticker you'll see a $27 credit for "delete functional ram air" as they had to rivet a blocking plate on the shaker opening to close it In order to pass the noise regulations.

There is some great spy trivia on how the Pontiac engineers tried to pull a fast one on the EPA by figuring out a special solenoid that would shut down the emission control systems on the production cars two seconds after the EPA test timed testing procedure was done. The EPA found out about it and GM got slapped big time. They had to completely redesign the emissions system and replace the camshaft with a milder one. That is why there is an initial rating of 310 hp and a production rating of 290 hp. That was one of the reasons that the engine package was delayed until the last couple weeks of production. It barely made it as the top brass at GM wanted to kill the whole deal but the engine plants had already built the 1,000 or so engines in a rush, seeing the writing on the wall. It would have cost too much to crush the motors, so they made the cars and got them out on the street.