Pontiac Trans Am 1978 images

A 1978 Pontiac Trans Am could hide two completely different personalities under the same cross-hatch grille that year. Order the standard 400 and you got a workmanlike 180 horsepower; check the right option box and Pontiac’s W72-code heads bumped that to 220 horsepower off nothing more than a smarter combustion chamber design. Here’s what actually separated a good 1978 Trans Am from a great one – and why the base engine wasn’t even a Pontiac.

The biggest external change for 1978 from the previous year is the cross-hatch patterned grill. The Firebird Formula LT Sport Edition has the same basic 305 cid engine with a high performance 305 with a 10% higher compression rating, which kicks it up to 155 hp. The higher performance 400 cid engine also has an increase in compression by putting the 350 heads on the 400 block and is called the 6x-4 heads now puts out 220 hp.

Our thanks to Gateway Classic Cars for the images

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1978 sat right at the crossroads for the Firebird – the last great gasp of the muscle car era before insurance companies and emissions rules finished the job smog regulations started. Pontiac knew it, too, which is why the Trans Am and Formula got a handful of quiet but meaningful changes that year that a lot of buyers never noticed under the new cross-hatch grille. Two different 400 cubic inch engines were floating around dealer lots that model year, and the difference between them came down to something as unglamorous as cylinder head castings – yet it meant a real horsepower gap between two cars that looked identical from the curb. Which one did you actually get if you ordered a 1978 Trans Am, and how would you have known?

The Grille Wasn’t The Only Thing That Changed

The most obvious 1978 update was cosmetic – a new cross-hatch pattern grille up front distinguished the model year at a glance. Underneath, though, Pontiac was juggling emissions compliance with whatever performance it could still legally squeeze out. The Firebird Formula’s engine lineup got more complicated than it looked: the base engine option was actually a Chevrolet-sourced 305 small block, with Pontiac’s own 400 cubic inch big block available as the step-up choice.

Two 400s, One Badge

Order the standard 400 (Pontiac’s L78) and you got 180 horsepower at 3,600 rpm and a healthy 325 lb-ft of torque – respectable but not thrilling for a car still wearing a Trans Am badge. Pontiac’s engineers had a second option waiting, though: the W72-code 400 swapped in cylinder heads with smaller combustion chambers, raising compression and, with it, output to 220 horsepower at 4,000 rpm and 321 lb-ft of torque at 2,800 rpm – a 10 percent bump that made the W72 the engine enthusiasts actually wanted. Two Trans Ams sitting side by side that year could have drastically different personalities under identical sheet metal, all traced back to a single cylinder head casting number.

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