1987 Buick Gran National (GNX)

14 Stealthy Sleepers That Leave Supercars in the Dust

Supercars got into their stride in the late 1960s. The Lamborghini Miura heralded a change by adding a mid-mounted V12, creating the first proper supercar. But you don’t need a low-slung wedge to go fast; sleepers are every bit as fast, often quicker.

What is a sleeper? Any regular production car has the potential. Bigger engines and turbochargers transform a humdrum sedan or SUV into a street-legal supercar beater. As far back as the ’60s, General Motors dabbled with forced induction, cutting emissions and displacement in favor of smaller, more powerful engines. To this day, the Syclone and Typhoon are still incredibly quick. 

Ever since, supercar owners need to watch the rearview mirrors, waiting for an impromptu overtake from the next unassuming sleeper.

1. Lotus Carlton 

Vauxhall Lotus Carlton
Image Credit: WikiCommons.

A strong contender for the best sleeper car ever? Under GM’s guidance, Lotus transformed the ordinary-looking Cartlon into a speed machine that bewildered supercar owners with its performance. Aside from a few bulges and a couple of Lotus badges, what GM had here was a four-door rocket ship.

The most significant changes are with the engine. Lotus upgraded Opel’s straight six to 3.6 liters, augmenting the extra inches with a brace of Garrett T25 turbos. The changes were startling, endowing the rep-mobile with 377 hp. Further mechanical charges include a six-speed ZF S6-40 transmission lifted from the ZR-1. Such a potent combination proved devasting on the roads, the Cartlon powering to 60 mph in 5.1 seconds and flat-out reaching 176 mph.

2. Buick GNX

1987 Buick Gran National (GNX)
Image Credit: Mecum Auctions

How fast you can go is usually limited to your bottomless pockets. However, there are occasions when a humble coupe can out-drag top-tier supercars. Enter the Buick GNX, which is one such machine. Like the Cartlon, its laid-back appearance masks stellar performance. In a drag race over 1/4 mile, GM’s rocket ship had the edge over the Porsche 930 turbo.

Despite the Buick badge, McLaren Performance Technologies provided the magic sauce. Under the hood, factory-fresh GNXs underwent a Jekyll and Hyde transformation, emerging with a claimed 276 hp. Later testing revealed the power figure was closer to 300 hp, backed by 420 lb-ft of torque. Whatever the real story was, there is no escaping a sub-5-second 0-60 mph time. 

3. GMC Syclone

GMC Syclone
Image Credit: WikiCommons.

Don’t be fooled by the boxy pickup truck body. Otherwise, you might be staring at a pair of fast-receding tail lights. Combining speed and a genuine load-carrying bed, the Syclone was all things to all gearheads. To supercar owners, it’s humbling another story.

Devoid of aerodynamic streamlining, the Syclone relied on brute force. Power came from a turbocharged LB4 V6 driving all four wheels through a 4-speed automatic transmission and BorgWarner transfer case. The benefit of all-wheel drive is more grip; in the Syclone, 280 hp proved enough to embarrass Ferrari 348 owners with a 0-60 mph time of 4.3 seconds.

4. Kia K900

Kia K9 / K900
Image Credit: Damian B Oh / Wiki.

Most famous for luxury cars and a wide range of SUVs, Kia doesn’t immediately come to mind if you want speed without bragging about it. The K900 is a perfect example of what you see isn’t always what you get. On the outside, a modern four-door sedan that blends into the background with minimal effort. Yet, range-topping K9s are hiding a secret.

Under the hood, Kia/Hyundai’s shared technology GDI V8 packs a 420 hp punch, launching the 4775-lb sedan to 60 mph in 5.2 seconds. While it won’t outpace a Hurracan or McLaren 720s, anything in the lower supercar leagues will be in for a surprise.

5. Jaguar XJ-R575

Jaguar XJR575
Image Credit: Jaguar Cars.

No list of sleepers would be complete with a Jaguar. During its final incarnation, Jaguar lost traditional styling cues, opting for a more sedate, modern body in the X351. While these designers were playing softly, the engineers had other ideas. Wafting around town, you would never guess how quickly the big cat can move.

Adorned with discrete badging, it does little to give the game away, but when you step on the loud pedal, it all becomes apparent quickly. Upfront, Jaguar’s long-running 5-liter Supercharged V8 punches out a lag-free 575 hp backed with 516 lb-ft of torque. Big numbers for any car, let alone a luxury sedan. When push comes to shove, the XJ-R easily holds its own in a sprint race, reaching 60 mph in 4.2 seconds.

6. Cadillac CTS-V

Cadillac CTS-V
Image Credit: WikiCommons.

It is a genuine halo car for Cadillac, and gearheads are unlikely to forget it quickly. Launched in 2004, the CTS-V turned out to be a masterstroke, helping to transform the carmaker’s luxury image into something more exciting. Think of the CTS-V as a Corvette in drag, and you’re on the right track.

Sleeper status comes from a C5 Z06 engine and transmission crammed into a GM Sigma platform. The process was trickier than simply bolting a big engine into a sedan. A custom engine cradle, beefier roll bars, and uprated springs set it apart from V6 CTS cars. Firing up the 5.7-liter LS6 and unleashing 400 hp proved what you see isn’t what you get.

7. VW Golf R

2023 Volkswagen Golf R
Image Credit: Volkswagen USA.

Through numerous GTi incarnations, the Golf has always been about affordable performance. However, it’s not the GTi you want. For the ultimate hot hatch sleeper experience, you need the Golf R. Extracting more performance, VW upped the engine boost level, yielding 315 hp from a small 2-liter four-cylinder engine. It’s impressive stuff, but there is more to come.

In a smiles-per-dollar contest, VW has a winner on its hands. At $45,000, gearheads won’t find anything that accelerates so quickly. The Golf R (manual) posted a 0-60 mph time of 4.7 seconds, easily outpacing Porsches 911 (992) Carrera T.

8. Tesla Model S

Tesla Model S Plaid
Image Credit: Tesla.

The secret behind the Model S’s performance is out, thanks to millions of Tesla owners. Even so, its world-beating performance numbers still surprise gearheads who believe it’s just an electric car. Hiding in plain sight, Tesla’s successful battery and twin electric motor setup delivers 789 hp.

However, it’s not the colossal horsepower figures that catapult the Model S toward the horizon at mind-blowing speeds. Unlike gasoline engines, electric motors deliver instant torque no matter your speed; for the Model S, that equates to 920 lb-ft. How fast? In P100D specification, 60 mph requires 3.1 seconds.

9. Audi S8

2024 Audi S8 Sedan
Image Credit: Audi Media Center.

Occupying Audi’s top slot, the S8 appears as exciting as a Sunday afternoon trip to the garden center. But when called upon, Ingostadt’s finest is devastatingly quick. Line alongside one of these at the lights, and you’ll lose in a drag to the next set. Audi is so confident in its car’s abilities that it only offers one engine choice paired with an 8-speed automatic transmission.

Boasting one of the most significant modern engines, a turbocharged 563 hp 4-liter V8, the S8 scorches to 60 mph in 3.8 seconds and is only reined in by an artificial limiter at 155 mph. Over the years, Audi has become very adept at building fast, discrete cars, which are everything you need in a sleeper.

10. Chrsyler 300C

2023 Chrysler 300C
Image Credit: Stellantis USA.

Tell-tale special or hot edition badges are a dead giveaway for sleeper cars, as the Chrysler 300 SRT proved. Every gearhead knew the SRT tag meant big numbers resided under the hood. Chrysler smartly realized less is more, at least when it came to branding. Enter the 2023 Chrysler 300C, same car, same engine, and a few extra horses.

This sleeper is one last hurrah for the 300C before bowing out. It boasts a 6.4-liter HEMI cranking out 485 hp. The gains might be small, but that doesn’t change how the car drives. Steeping on the gas pedal deploys a tidal wave of torque, dispatching in-gear acceleration times with frightening speed.

11. BMW M340d

BMW M340d sedan
Image Credit: BMW Media.

Diesel is a dirty word usually associated with scandalous emissions rigging. Also, diesel cars are typically slow and noisy, standing no chance in performance circles. In reality, the results are not so clear-cut. BMW tuning division M worked its magic on the venerable 3-series, squeezing a 335 hp 3-liter straight-six diesel under the hood.

It’s easy to forget that diesel engines produce less horsepower and more torque. The latter is what makes the M340d stand out. It boasts 516 lb-ft of torque, enough to reach 60 mph in the low 4-second range and run to a top speed of 160 mph. The M340d is quick enough to worry junior supercars in a sprint race.

12. Pontiac G8 GXP

2008 Pontiac G8 GT
Image Credit: WikiCommons.

One of the all-time great muscle car markers, by the 1990s, Pontiac was a shadow of its former self. That’s not to say Pontiac couldn’t build fast cars; it was more a case of financial restraints. Before bowing out in 2010, the G8 GXP provided a glimmer of what Pontiac once stood for.

Understated styling based on an imported Holden sedan hides a potent sleeper waiting to be released. Both Holden and Pontiac fell under the GM umbrella, which granted access to the LS series engines. The G8 GXP borrows heavily from the Corvette, using a 6.2 liter LS3 motor paired with a 6-speed automatic transmission. Official figures put the GXP in the low 4-second range up to 60 mph.

13. Alpina B7

BMA Alpina B7 (G12)
Image Credit: Alexandre Prevot / WikiCommons.

BMW M-sport king of the factory-produced sleepers? There are ways to go even faster without resorting to third-party after-market mods. Like the BMW M division, Alpina is an entirely in-house affair, providing the ultimate driving machine with even more performance.

Sitting between the standard car and the BMW 760i, Alpina’s B7 delivers similar power figures with a smaller, lighter engine. Swapping out the 6.6-liter V12 for a more compact 4.4-liter biturbo unit yields a nearly identical 0-60 mph time. However, in challenging the 200-mph club, Alpinas’ less-is-more approach wins out at 205 mph.

14. GMC Hummer EV SUV

GMC Hummer EV SUV
Image Credit: GMC.

The Hummer will never win any beauty awards, nor will its brick-like profile endow it with a low drag-coefficient number. But that’s not to say the 8600 lb Leviathan isn’t quick off the line, far from it. In a drag race, 60 mph comes and goes in 3.4 seconds, meaning anything less than the fastest supercars will be left standing.

The secret to its blistering performance is in the name. Adopting an EV battery and motor setup for propulsion transformed the former military work-horse into a monster boasting 830 hp. Who would have thought the quickest sleeper cars would take on an SUV form?

Jason Garbutt

Author: Jason Garbutt

Title: Business Development Managger

Expertise: Cars, Military Vehicles, Computers, Gaming Consoles, Aviation, Movies

Bio:

From a young age, vehicles of every shape and size significantly impacted Jason. But a surprise birthday gift of a ZAP racing kart ignited the spark in earnest. Cars, planes, military vehicles, and ships have been the center of attention ever since.

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