The problem originates in the technical understanding of what constitutes a true D-PORT versus a D-shape. The D-Port roof extends well above the centerline of the exhaust port, whereas the D-shaped port fits nicely inside what is deemed a standard port dimension. As shown in the graphic below, the d-shape easily fits within the common round or square port flange opening. Many specialty header designs such as Lake Headers, Lake Pipes, and Zoomies are designed to be era correct for certain car builds.

Most of our techs agree that a street application 350 will benefit well from a header with 1 ½” to 1 5/8” diameter primary tubes and 2 ½ or 3 inch collectors. What this size does is creates a faster removal of spent gas and also develops just enough backpressure for a broad torque response. This marked the final production year for the Third Generation platform. Release of the Fourth Generation model was imminent, and Pontiac made few changes to the 1992 Firebird.

The 5.3-liter Vortec V8 was installed in 2022 and is said to have been sourced from a 2002 Chevrolet Tahoe. An Edelbrock air cleaner, an aluminum radiator, electric cooling fans, and Speed Engineering long-tube exhaust headers have been fitted. The Vortec 7400 L21 was a commercial version of the Chevrolet big-block engine used in the medium duty truck platform. Its design shared much with the L29 454, but with the addition of forged pistons and crankshaft, and coil near plug ignition.

GM replaced many sets with tops made of glass under warranty, but the acrylic tops continued as standard-issue through 1992. All Firebirds optioned with rear disc brakes now received PBR brake calipers and larger brake rotors, which resolved issues encountered with previous-model rear discs and increased stopping power. Introduction of GM’s Vehicle Anti Theft System (VATS) or PASS-Key made all Firebirds more theft-resistant. The system was adapted from GM’s higher-end Corvette and Cadillac vehicles in response to an escalating trend among car thieves to target the Camaro and Firebird. VATS incorporated a small resistor into the ignition key shaft which was read by a sensor when the key was inserted.

This also allowed GM to experiment with some of the new technologies which were to be implemented on the fourth generation cars. The Formula was the only third-generation F-body to get to T-tops with a 350 cubic inch engine starting in MID year 1991 &amp