No car company will admit to underrating a car’s horsepower to keep flagship sales intact. Vehicles like the Chevrolet Corvette and Ford Mustang are performance bread and butter. If a more powerful car were to debut, sales of those flagship models could suffer. This is all speculation, so take it with a grain of salt. However, some of these arguments can be compelling.

Mercury Marauder vs. Ford Mustang

It’s entirely possible Ford underrated the Mercury Marauder’s horsepower to protect Mustang sales. The Marauder was the 2003-equivalent to the Blues Brothers’ 1974 Dodge Monaco. It was an undercover streetcar, the Crown Victoria, with police suspension, brakes, and engine. The Marauder enjoyed the sweet sounds of the dual-overhead-camshaft modular 4.6-liter V8 and 300 horsepower, which was less than the Mustang was making with the same engine a couple of years prior in the Cobra, at 360. This is just a rumor, but an interesting possibility.

Trans Am/Camaro/Grand National vs. Chevrolet Corvette

In the early 2000s, the Pontiac Trans Am, Chevrolet Camaro, and Chevrolet Corvette had the same engine, the LS1 5.7-liter V8. It was an overhead valve aluminum engine that got 345 horsepower in the Corvette, yet the Camaro and Trans Am only got 305. There was no way the lesser Trans Am and Camaro could outshine the Corvette, so they may have been given underrated horsepower figures. According to Chevrolet’s unwritten rule, no car in its lineup may surpass the Corvette. Rumors abound that GM killed the Buick Grand National for the same reason: it was too fast. 

Pontiac Fiero vs. Chevrolet Corvette

The Pontiac Fiero is an interesting case in the context of underrated horsepower. It was a tiny mid-engine sports car, and the biggest engine offered was a 140-hp V6 in the Fiero GT. Hulki Aldikacti, who designed the Fiero, built a prototype Fiero which he said beat the Corvette candidly. This variant employed a twin-turbo V6, according to Calgary Fiero Owner’s Club. Unfortunately, his team was caught doing it, according to Aldikacti, and to add insult to injury, they lacked the budget to put it into production. A document shared on the Fiero.nl forum outlined an incident when a turbocharged Fiero outran the new Corvette C4 on a test track, and the project soon halted after that.

2003 Mercedes-Benz E55 AMG vs. SL600

As the fastest sedan in the world for its time, the 2003 Mercedes-Benz E55 AMG was almost a supercar. It used a supercharged 5.4-liter V8, producing (officially) 470 horsepower. However, individual owners dyno tested it closer to 510 horsepower at the crank. At the same time, the twin-turbocharged V12-equipped Mercedes-Benz SL600 made an advertised 493 horsepower, so it’s believed Mercedes-Benz underrated the E55’s power on purpose to avoid outshining the SL600. It’s another rumor but a discrepancy worth considering. 

Whether these cars and horsepower figures tell a story or defend a conspiracy, it’s essential to consider that it’s not unheard of for car companies to fudge horsepower values. If you’re out for a used car, and can’t decide between a 2000 Pontiac Trans Am or Chevrolet Camaro, consider the Trans Am as probably capable of making the same power without needing much encouragement.