Buick Rated the 1970 GSX Stage 1 at Just 10 More Horsepower – Real-World Testers Called It a Hemi Killer Anyway

Buick’s 1970 GSX Stage 1 carried a horsepower rating that barely budged from the base engine, a number built for insurance adjusters, not drag strips. Decades later, owners and historians are still fighting over whether it really deserved the Hemi Killer nickname, or whether a mismatched magazine test built a legend that never quite held up.

Buick’s engineers built one of the fastest street cars of 1970, then undersold it on the window sticker by design. The GSX Stage 1 package added barely any horsepower on paper — a number insurance underwriters, not drag strip judges, were meant to read. When an independent road test finally got a Stage 1 car on a real strip, it ran a 13.38-second quarter-mile at 105.5 mph, a time that embarrassed cars wearing far louder badges. More than fifty years later, GSX owners and Hemi ‘Cuda owners are still arguing about which 1970 legend actually deserved the bigger reputation.

The Buick Nobody Expected to Win a Drag Race

That argument is the entire premise of V8TV’s “1970 Buick GSX and 1970 Hemi ‘Cuda Rivalry,” a Muscle Car of the Week episode built around putting Buick’s halo muscle car next to Plymouth’s 426 Hemi-powered E-body and letting the two cars speak for themselves. Host Kevin walks around both cars at V8 Speed & Resto Shop, and the video treats the pairing less like a technical comparison and more like a reunion of two old rivals who never actually agreed on who won.

The video leans on the GSX’s reputation as the “underdog” of the muscle car wars — a luxury-oriented Buick that nobody expected to run with Hemi-powered Mopars — while giving the Hemi ‘Cuda its due as the car most enthusiasts still assume wins any straight-line argument by default. It’s a format V8TV has built a following on: two genuine, unrestored-feeling muscle cars shot up close, minimal narration, and comment sections that turn into their own debate stage long after the video ends. Nothing about either car looks trailered-in or staged for a photo shoot — both wear the scuffs and patina of cars that actually got driven, which is part of why the rivalry still feels personal to the people arguing over it.

⚑ Featured Gear

Start Car Conversations →

As an Amazon Associate I earn from qualifying purchases.

How a Buick Became a Muscle Car in the First Place

The GSX wasn’t Buick’s first swing at performance. The division had been building Gran Sport models since 1965, chasing the same buyers the GTO and the Chevelle SS were courting, but Buick’s conservative, country-club image made it a hard sell as a street brawler. That changed in 1970 when Buick’s engineers paired the new 455 cubic-inch big block — the largest engine GM allowed in an intermediate that year — with a dedicated appearance and handling package and gave it its own name: GSX, for Gran Sport Experimental. It got its own stripes, its own domed hood, a rear spoiler, and just two color choices, Saturn Yellow or Apollo White, so that nobody mistook it for a base Skylark.

Buick built only 678 of them that first year, and of those, just 479 carried the Stage 1 performance package — 280 with the automatic transmission, 199 with a manual. The standard 455 cubic-inch V8 was already rated at 350 horsepower and a massive 510 lb-ft of torque, numbers that made the GSX one of the highest-torque production cars in America at the time, Hemi included.

Why Buick Lied About Its Own Horsepower

Stage 1 was supposed to be the serious version: a 10.5:1 compression bump and a more aggressive camshaft on top of the standard 455. But Buick’s official horsepower rating for Stage 1 barely moved — only about 10 horsepower over the base engine, with torque left unchanged on paper. Most historians now agree the real gain was closer to 25 to 40 horsepower, quietly withheld to keep insurance premiums from torpedoing sales. It was the same trick GM played across its muscle car lineup that year, and it’s exactly the kind of gap between the sticker and the stopwatch that fuels comments like the ones under this video, where longtime owners argue about whether their own Stage 1 cars ever ran as quick as the numbers claimed.

That underselling habit wasn’t unique to Buick. Ford ran a similar game a few years earlier with the Torino, a car that won consecutive NASCAR championships with David Pearson behind the wheel before Hollywood turned it into the “Striped Tomato” of Starsky & Hutch — proof that Detroit’s muscle car era was full of cars whose real-world capability outran, or in some cases never quite matched, their public image.

The “Hemi Killer” Debate Nobody Settles

Enthusiasts have nicknamed the GSX Stage 1 the “Hemi Killer” for decades, and the comment section under this video shows exactly why the title never fully sticks. One commenter points out that the magazine numbers often cited to justify the nickname pitted a 1970 Stage 1 against a 1969 Hemi ‘Cuda — not a direct, same-year matchup — and that Chrysler had quietly improved the 426 Hemi’s valve lift between those two model years without changing its advertised rating. Others in the thread say their own real-world Stage 1 cars, running stock street gears and factory exhaust, were never as quick as the numbers that built the legend, and suspect the test car was tuned beyond what a buyer could get off a dealer lot.

It’s the same argument that’s followed muscle cars since the day they left the factory: a magazine’s test numbers, run under ideal conditions with a specially prepped car, rarely matched what showed up in a customer’s driveway. The GSX Stage 1 and the Hemi ‘Cuda both earned reputations built partly on legend and partly on a stopwatch, and neither side has ever fully convinced the other — which is exactly why a video pairing the two, more than fifty years later, still pulls fans into the same fight their fathers were having in 1970.

What Still Makes the GSX Worth Arguing About

Scarcity is a big part of it. With only 479 Stage 1 cars built in 1970 and total GSX production falling further to 124 units in 1971 and a mere 44 in 1972, the car never got the chance to become common the way a Chevelle SS or a GTO did. That rarity, combined with a torque number that still reads as absurd more than fifty years later, is why collectors treat an original Stage 1 GSX as one of the most underrated muscle cars GM ever built — a car that out-torqued nearly everything on the road in 1970 while wearing a Buick badge nobody associated with speed.

It also helps that the GSX never had to carry Buick’s performance reputation alone for long. By 1971, insurance pressure and tightening emissions rules were already squeezing every manufacturer’s muscle car lineup, and GSX production cratered the following two years before the nameplate quietly disappeared. That short window — essentially one real model year of the car most people picture when they hear “GSX” — is part of why the Stage 1 package still commands serious money and serious debate at every car show it appears.

Whether or not it ever truly out-ran a same-year Hemi ‘Cuda is beside the point by now. The GSX did exactly what Buick needed it to do in 1970: it beat cars it had no business beating, kept its real numbers off the insurance company’s radar, and left behind a rivalry that’s still being argued in YouTube comment sections more than half a century later.

Watch the full video above and let us know your thoughts in the comments.