A fast car that looks the part is a good thing, but not nearly as satisfying as having an ordinary looking machine with the heart of a lion. Drivers of such cars don’t have anything to prove, but they can bathe in the warmth of knowing that, if required, they’ve got the firepower. They might never use it, but it’s just good to know it’s there.

There are other advantages, too; if you’re driving something that looks innocuous or even a bit weedy, the police are not going to pay you any mind. And nor will you have stop-light-junkies revving their engines in challenge.

This class of cars, often called "sleepers," are best when produced by brands that historically don’t have a record of building hysterically fast machines. When, for example, people think of Volvo, they imagine a very safe but ultimately dull family car. Which is why the explosively quick T5R is such a hilarious surprise.

Another, slightly less inspiring class of cars are those that look fast but simply don’t deliver on the promise. They are usually the result of marketing departments looking to lure buyers with sleek bodies and all the visual cues of power and performance. But it costs money, and quite a lot of it, to engineer and properly develop a high-performance powertrain. If the funds aren’t there, it’s easier to talk the talk and take a pass on walking the walk. That’s how you end up with posers like a Pontiac Firebird with an asthmatic four-cylinder motor.

20 Looks Slow But Is Fast: 2015 Brabus Maybach Rocket 900

The Mercedes-Maybach S600 is the very definition of luxurious wafting, complete with champagne flutes in the rear console, a soothing, vault-like quiet and the most dignified imaginable progress down the road. It feels properly regal. Well, German tuning company Brabus decided to give the Maybach a little more attitude. No, actually, a lot more attitude.

They took the existing 525hp 6.0-liter V12 and bored it out to 6.3-liters, slapped on larger turbochargers and worked their tuning magic.

Topgear.com described its performance as a little scary: “This Brabus version does 62mph in 3.7 seconds - on par with a Ferrari FF - and will merrily, terrifyingly rock on to a top speed of 217mph.” If you’re giving that a go, best put the champagne glasses away.

19 Looks Slow But Is Fast: 2018 Jeep Grand Cherokee Trackhawk

For high-plains drifters looking for a bit of outback adventure, the Grand Cherokee has for decades delivered offroad ability matched by few. It offers a fine blend of utility and toughness, but taking in its rugged stance and high-riding style, you probably wouldn’t guess that it also offers Ferrari-grade performance.

That’s right, this Jeep packs the Hellcat V8 also found in the Dodge Charger and Challenger Hellcat. Road and Track magazine says that the Hellcat Jeep is the most powerful SUV in the world, with a supercharged 707hp V8. And Jeep says this is also the world's fastest SUV, reaching 60mph in 3.5 seconds and maxing out at a ballistic 180mph. Yippee-ki-yay!

18 Looks Slow But Is Fast: 1996 Volvo 850 T5R

After decades of churning out large, boxy, anonymous – but exceedingly capable – station wagons, Volvo did something extraordinary. The company unleashed the T5 in the early 1990s and then the T5R, the latter a wailing, five-cylinder flier that challenged every preconception about what Volvos were about.

At its press launch, Volvo convinced the Swedish authorities to close a large section of four-lane divided highway. Journalists were invited to drive the 250hp wagons as fast they’d go, which was about 150mph.

With its lowered suspension and available graphite finished wheels, here was perhaps the first actually cool Volvo, but you had to be a proper gearhead to realize what you were looking at – the T5R wagon’s reputation was further burnished when they were campaigned in the British Touring Car Championship.

17 Looks Slow But Is Fast: 2003 Mercury Marauder

Like it’s stablemate Crown Victoria, the Grand Marquis was a hit with taxi companies and motorist of a certain age across America. What it wasn’t was a terribly exciting machine and so younger drivers tended to stay away. To boost the car’s appeal to a younger audience, parent company Ford set out to create a Grand Marquis with a more dangerous, hotrod-ish feel. Enthusiast site Japopnik.com said of the Marauder: “When you get down to it, this was probably the last cool Mercury of any sort.”

To create a bit of menace, the Marauder was offered with black paint, blacked out grille and big 18-inch alloy wheels sitting on lowered suspension. It does look pretty cool, and with the Mustang Cobra 4-valve 302hp V8 lurking under the hood, the Marauder will make 60mph in about 7 seconds.

16 Looks Slow But Is Fast: 1992 Mercedes Benz 500E

Hoards of Mercedes Benz E-class sedans work long and hard lives as taxis in every major German city. They just blend into the background, and for many observers, that’ll be true for the 500E. There is little to give away the fact that this is one of the most legendary E-class models ever created, apart from swollen wheel arches sitting over 18-inch wheels.

In the 1990s the 500E was virtually hand-built by Porsche in what had been its 959 factory – under the hood lies one of Mercedes’ greatest ever V8s, a 326hp charger that reaches 60mph in just 5.5 seconds and is capable of 170mph. That’s seriously quick by any measure.

15 Looks Slow But Is Fast: 1968 Plymouth GTX Hemi

One of the most collectible examples of "sleeper" muscle cars, the GTX Hemi was based on the cooking Belvedere platform. Touted as a "gentleman’s muscle car," the GTX was a little more subdued than stablemates such as the Road Runner.

Sure, the GTX was "subdued" until you uncorked that mighty, optional 426 cubic-inch Hemi V8, which developed a titanic 425hp. A four-speed manual gearbox was optional, and the favored pick among race fans, and with a 0-60mph time of fewer than five seconds, the Hemi’s performance was hugely impressive for the era. And as a measure of how well regarded the GTX Hemi is, a matching numbers example can sell for well over $100,000. It has rarity going for it too, as howstuffworks.com observed: “Die-hard racer types loved the Hemi, but just 450 GTXs were ordered with the $564 [Hemi] option.”

14 Looks Slow But Is Fast: 2017 Chevrolet SS

The Chevrolet SS is another great example of a car that observers would never guess is a performance giant – the rather pedestrian, four-door styling doesn’t give any clues to what’s going on under the hood. Namely, a thunderous 415hp 6.2-liter V8 from the previous generation Corvette and Camaro.

Provenance doesn’t come much better than that, and with 60mph flashing by in 4.5 seconds, this Chevy is extremely quick. The SS, which is no longer on sale, was basically an Australian Holden Commodore wearing Chevy clothes.

And unusually for such a large car, the SS has good handling agility and is a hoot to drive on challenging country roads. As Car and Driver magazine said: “Balance is a word that rarely applied to big Chevrolet sedans in previous decades, but the SS has it.”

13 Looks Slow But Is Fast: 1990 Lotus Carlton

Beneath the somewhat dumpy and upright lines of this four-door sedan lurks the heart of a supercar. Indeed, in its day, the Lotus Carlton actually had more performance and speed on offer than most supercars.

The Carlton that this remarkable car was based on was a fairly ordinary mid-level executive sedan in the UK and Europe. That’s what makes it so interesting.

Sports and race car builder Lotus took on the project, first enlarging the straight-six engine and adding twin turbochargers. The result was 382hp, which resulted in breathtaking performance with 60mph reached in 5.2 seconds and a top speed near 180mph. The only clues to the huge performance were flared wheel arches, vents on the hood and a spoiler on the trunk.

12 Looks Slow But Is Fast: 2004 VW Phaeton W12

The Volkswagen Phaeton was Volkswagen’s attempt to enter the premium end of the market to compete with prestige marques like Lexus, BMW, and Mercedes-Benz. The Phaeton shared its platform with no less than the Bentley Continental and Flying Spur, as well as the Audi A8.

The Phaeton features a rather staid and unadventurous exterior but its real party trick is the 6.0-liter W12 option (twelve cylinders in a W formation), which it shared with the Bentley Continental. At a glance, the W12 looked no different than lowly V6 versions of the Phaeton, but with that thundering W12 and four-wheel drive, it could scramble to 60mph in 5.7 seconds and on to 155mph.

11 Looks Slow But Is Fast: 2007 BMW M5 Touring

BMW’s quite handsome M5 Touring wagon is, at a glance, a regular grocery hauler with a spacious cargo area and family-friendly space inside. While all of that is true, there’s a little secret under the hood, one that will have enthusiast drivers wide-eyed in disbelief.

This M5 is claimed to be the world’s first production sedan offering up a V10 engine. Keen-eyed observers might just notice the wider wheel arch flares and the front fender cooling vents. With 507hp to call upon and shifting through a seven-speed sequential gearbox, the M5 wagon could hit 60mph in a shade over 4.2 seconds and blast on to a top speed in the region of 200mph. Car and Driver magazine reckon the M5 is the real deal: “In the automotive world, BMW’s M5 has long been one of the standards against which all other sport sedans are judged. That goes for wagons, too.”

10 Looks Fast But Is Slow: 1980 Chevrolet Corvette

The Chevrolet Corvette has, for decades, represented the very best of domestic sports cars. Beautifully styled, it features flowing lines and the traditional long hood and short trunk favored by sports car designers. And historically, you could count on thunderous horsepower from massive V8s.

In 1980, not so much. Leading up to that year, emissions regulations stymied once towering horsepower figures, and nowhere as much as California, which had some of the toughest regulations going.

So by 1980, the California spec Corvette had a relatively small 305 cubic inch V8 with just 180hp – other states still had the option of a 350 V8 with up to 230hp. So if you were unlucky to end up with the California spec ‘Vette, you’d be lucky to break 8 seconds to 60mph

9 Looks Fast But Is Slow: 1982 Pontiac Firebird

The Pontiac Firebird was yet another iconic American muscle car with such striking looks and performance that a Trans Am Firebird starred alongside Burt Reynolds in the massively popular movie Smokey And The Bandit. The Firebird had originally launched in the late 1960s to take the pony car battle to Ford’s Mustang and in-house rival Chevrolet Camaro. In the early 1970s, Trans Am Firebirds with massively powerful 455 cubic-inch V8s hit the scene.

And then a combination of oil embargoes and emissions regulations saw power outputs plunge through the 1970s. Installing smaller and smaller V8s was one answer, and in 1982, things went even further, with Pontiac offering a Firebird with a 151 cubic-inch four-cylinder engine producing just 90hp. Firebird? Fizzlebird, more like.

8 Looks Fast But Is Slow: 1982 DeLorean DMC-12

Even today, the DeLorean DMC-12 looks like a proper supercar. It features gullwing doors, a wedge-like profile that would look at home on a Lamborghini and a starring role in a hit movie. Bob Gale, the writer of Back to the Future told popularmechanics.com “the filmmakers chose the DeLorean because it resembled a futuristic spaceship and it looked like a homemade time machine.”

Good so far, but those who took the plunge and bought a DeLorean soon discovered that the car didn’t have the performance to match its looks, not by a long stretch.

The problem was the car weighed far more than anticipated and the breathless Renault V6 couldn’t cope. But it is still a great looking car.

7 Looks Fast But Is Slow: 1983 Ford Mustang GT Turbo

The name alone suggested that the Ford Mustang GT Turbo would be a real flier. But that just wasn’t the case as its 2.3-liter four-cylinder powerplant lacked the poke that you’d expect from Ford’s bold graphics. With just 145hp under the hood, this Mustang couldn’t run with the faster V8 competition.

And as howstuffworks.com said: “[The Mustang’s] peaky engine was relatively weak on low-rpm torque, so it had to be caned most all the time. The [Mustang’s] V-8, by contrast, was a traditional, relatively lazy American engine with muscular low-end thrust.” The GT Turbo was a sales flop in the end, not least because it was actually more expensive than the faster V8 Mustang GTs.

6 Looks Fast But Is Slow: 1991 Honda Beat

For left-field car choices, the Honda Beat is right up there with the best – this tiny Kei car (that’s a tax-beating class of car in Japan) packs an equally small 660cc triple-cylinder engine with 63hp. And enthusiast site Jalopnik.com reckons it has potential: “This Beat pushes a lot of the right buttons. These are cool mid-engine convertibles, just like the Porsche Boxster, MG TF, and the Toyota MR2 Spyder.”

The thing is, though, it needs a proper turn of speed to justify those cool, mid-engine looks. And a 0-60mph time of a little over 13 seconds and a top speed of just 84mph makes it the slowest car on our list.

5 Looks Fast But Is Slow: 1997 Plymouth Prowler

Fans of traditional American hot-rods went wild when Chrysler put the Prowler into production in 1997. Virtually unchanged from its 1993 concept car form, the car wore a Plymouth badge and all the attitude of a 1950s hot-rod.

There was just one crucial problem with the Prowler (well, two, actually). Firstly, a 3.5-liter V6 resided under the hood, where hot-rod purists would have expected to find a thumping big V8.

The second issue was an unresponsive and clunky gearbox. As carbuzz.com said: “Later cars were given an all-aluminum V6 with 253 horsepower, but it was still hampered by that awful automatic transmission.” The lesson, as always, is don’t give a car looks that its powertrain can’t back up.

4 Looks Fast But Is Slow: 2003 Smart Roadster

With its mid-engine layout, Targa roof and long hood, short trunk visuals, the Smart Roadster has the sports car look nailed. However, if observers assume that it packs the performance of, say, a small Lotus Elise, they’ll be in for a surprise.

The Smart Roadster features a tiny 698cc three-cylinder engine with a paddle-shift six-speed automatic transmission.

As Car And Driver observed, it’s a bit slow: “We're talking 10.7 seconds to 60 mph and a quarter-mile of 17.4 seconds at 76 mph, coincidentally almost exactly the same numbers as a Hummer H2's.” On the positive side, no matter how hard you drive the Smart Roadster, it’ll never get much less than 35mpg.

3 Looks Fast But Is Slow: 1976 Porsche 924

It is generally accepted that anything with a Porsche badge on its nose is going to be quick and handle like a thoroughbred. And while it is true that the Porsche 924 is decently agile through the corners, it will hardly set the motoring world on fire. It was also the first Porsche to feature an engine in the front and available automatic transmission.

The 924 was meant to be the entry-level model that would replace the 914. Developed with Volkswagen, and using a Volkswagen Group four-cylinder engine, the cheapest Porsche would also be the slowest. Still, it proved popular as evo.com in the UK observed: “While performance was relatively low by Porsche standards the draw of an entry-level Porsche was as strong then as it is today, and it sold well.”

2 Looks Fast But Is Slow: 1984 Pontiac Fiero

With its low-slung mid-engine looks, the Pontiac Fiero had all the makings of a credible challenger to European sports cars. But the reality wasn’t nearly as rosy – the Fiero was expensive to maintain and plagued with unreliability.

And as motor1.com said, the performance from its 2.5-liter four-cylinder engine was glacial: “Thanks to its weight of more than 2,500 lbs, the Fiero was slow, really slow. Real road tests performed by Car and Driver in December 1983 showed an uninspiring 0-60 miles per hour acceleration in 11.3 seconds and a top speed of only 105mph for the base model.” It does, though, hold the distinction of being the only mass-produced mid-engine American car.

1 Looks Fast But Is Slow: 2016 Honda CR-Z

The Honda CR-Z looks convincingly quick with forward-leaning swages in the body and a low, ground-hugging nose. Its styling recalls that of the 1980s Honda CR-X, a car hugely popular with enthusiast drivers.

Car and Driver editor Csaba Csere said: “With its sporty two-seat design, excellent performance, and nimble handling, [the CR-X] can also be viewed as the reincarnation of the low-priced sports car.”

That’s what Honda was aiming at with the 130hp CR-Z. It missed. Car and Driver said of the CR-Z, “Since its 2011 debut, the CR-Z—Honda’s self-proclaimed successor to the CRX—has missed the bulls-eye of both its targets, namely being sporty and efficient.” Ouch.

Sources: roadandtrack.com; honestjohn.co.uk; popularmechanics.com; caranddriver.com; musclecars.howstuffworks.com; jalonik.com; autocar.co.uk; motor1.com