Pontiac Firebird 1973 – LOUD Startup Sound and Acceleration

A 1973 Pontiac Firebird with a loud, aggressive startup usually means one thing: real engine underneath. We look at Pontiac’s last big swing at genuine muscle before emissions rules closed the era, including the ultra-rare Super Duty 455 that Pontiac only built 43 times that year.

“Highly tuned!”

“Highly tuned” is doing a lot of work in two words, but if you’ve ever heard a properly built 1973 Firebird come off idle, you understand exactly what that means. This was the last stand for Pontiac’s big-inch muscle before emissions regulations closed the book on the era, and the cars that came out of it — when built right — could still embarrass almost anything else on the road in 1973. A loud, aggressive startup out of a Firebird from this year isn’t just noise; it’s usually a sign of exactly how much engine is sitting up front.

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1973: Pontiac’s Last Real Swing at Big-Inch Muscle

The ’73 Firebird lineup ran from the base car up through the Formula and Trans Am, with the Formula offering a 350 two-barrel as standard and stepping up through a 400 four-barrel rated at 230 horsepower. At the top of the order sheet sat the L-75 455, and above that, the legendary Super Duty 455 — a genuinely different engine under the skin, not just a bigger carburetor bolted to the standard block.

The Super Duty 455 Nobody Was Supposed to Get

The SD-455 came with a stronger block, four-bolt main bearings, provisions for dry-sump lubrication, forged rods, and TRW pistons — real racing hardware wearing a production badge. Pontiac officially rated it at 310 net horsepower, though most SD-455s actually left the factory with a milder cam and closer to 290 horsepower in practice. Pontiac built only 43 SD-455 engines for the 1973 Formula that year, making a genuine, numbers-matching example about as rare as muscle cars from this era get.

What a Sound Like That Usually Means

A car that sounds this aggressive at idle typically means dual exhaust, an aftermarket cam, or a genuine SD-455 doing exactly what it was built to do — Pontiac claimed SD-455 cars could run 0-60 in under 5.5 seconds and cover the quarter-mile in as little as 13.8 seconds, even with an automatic behind it. Whether this particular Firebird is a numbers-matching SD-455 or a well-built driver chasing the same sound, it’s a reminder that 1973 produced some of the last genuinely quick muscle cars before the era shut its doors.

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