Like HowStuffWorks on Facebook!

1973-1975 Pontiac Grand Am


1973 Pontiac Grand Am Engineering

For the new 1973 Pontiac Grand Am, chassis engineers upped the suspension bushings from 60- to 90-durometer rubber and installed heavier grommets for the 1.12-inch front stabilizer. To counteract any tendency to oversteer, engineer Tom Seaton added a 0.94-inch rear antiroll bar. He also specified nonaerating Pliacell shock absorbers, with plastic inner bags that kept the air separate from the hydraulic fluid. This gave consistent damping even when hot, unlike conventional shocks, which, under severe conditions, tend to become mushy with aeration and heat.

Seaton then added 0.3 inches to the Grand Am's ride height for more suspension travel. And in the tire department he specified GR70-15 steel-belted radials on optional 15x7 Polycast honeycomb wheels.

Among the 1973 Pontiac Grand Am engine options were an L75 and a pair of 400 V-8s.
Among the 1973 Pontiac Grand Am engine options
were an L75 and a pair of 400 V-8s.

Entrusted with engine duties was Herb Adams' Special Projects group. Engineer and race driver Adams did his darnedest to match Pontiac's big-block V-8s to the Grand Am mission. Initially, he wanted to drop the Super Duty 455 into this car, and one Grand Am prototype did get built with it, but only that one, because GM decided not to use the 310-horse stormer in anything except the '73 Trans Am and Formula Firebirds.

The SD-455 was a good idea, though, one that would have effectively passed the performance torch from GTO to Grand Am. This engine added a mere $521 to the price of a '73 Trans Am and probably wouldn't have cost any more as a Grand Am option. Its initial 1973 horsepower and torque ratings were 310 and 390, but Pontiac rerated the engine at midyear to 290 and 395.

This was essentially a race-ready V-8 in street form: four-bolt mains, reinforced bulkheads, more meat around cam bearings and lifters, forged and lightened rods and pistons, nitrided cast crank, 80-psi oil pump, baffled pan, and built-in provisions for dry-sump lubrication. Heads were patterned after Pontiac's 1969 Ram Air IV engine, as were the cam and rockers. In all, only 1195 Super Duty 455s were ever sold, and more parts were stolen out of the plant than made it into production.

But while the SD-455 didn't show up in the Grand Am, some very good Pontiac V-8s did, starting with the L75, a "regular" four-barrel, dual-exhaust 455 rated at 250 bhp and 370 lb-ft of torque. Then came a pair of 400 V-8s, one with four-barrel carburetor, the other with two-barrel, respectively rated at 200 and 170 horses. (Optional dual exhausts boosted engine output.) Buyers could order either self-shift Turbo Hydra-Matic or Muncie M21 four-speed manual with floor shift, the latter teaming with a 3.23:1 rear axle.

Soon after the Grand Am's introduction, Herb Adams & Team Associates put together what Motor Trend described as "the most beautiful Pontiac stock car ever built." Team Associates was a wild group of Pontiac engineers who liked to go racing. GM had officially disavowed track competition nine years earlier, so Adams & Team Associates built and ran a Grand Am racer out of their own pockets. They had campaigned a GTO and a Firebird in the SCCA Trans-Am series and had done moderately well.

Now, with the Grand Am, they had their sights on the big time, notably NASCAR. They qualified and ran at Riverside in January 1973, starting and finishing 14th with no brakes at the end of that race. They then tried Daytona after jumping through an inordinate number of NASCAR inspection and qualification hoops, only to have their car blow a head gasket after qualifying at 169 mph; its 366-cid V-8 had too much compression. With that, and no major sponsors in sight, the team retired its gloss-black Grand Am #69.

For more information on cars, see: