Performance tuning is something of a mystery to most people, there are dozens of tuners out there who merely plug in a laptop, then there are the serious tuners who do things properly unlocking ridiculous amounts of power. There are certain mods that'll make a car faster, and others that are best avoided.
We have all seen adverts for plug-in ECU reflashing, promising big power gains without reliability issues made possible because carmakers sell us effectively detuned engines in exchange for reliability or fuel consumption. Engineering in a margin of error allows serious tuners to exploit the hidden potential, improving the engine's ability to suck in more air and fuel, ultimately producing more power, such as Hennessey when they built the 1000hp Camaro Exorcist,
How much more power varies, but some stock motors can easily yield double their factory specification producing truly stunning results. Although, that will sometimes require changing some other parts as well, such as intercooler, exhaust, turbos, and injectors.
10 Hennessey CTS-V HP1000 - 1000hp
No strangers to performance car junkies, Hennessey Performance produces some of the most outrageous power upgrades for what is often run-of-the-mill production cars. It's lways a good starting point to begin with something that's already fast. Cadillac's CTS-V is not exactly underpowered with 640hp from the factory, roaring to 60mph in 3.6 seconds should be fast enough.
Unsurprisingly, Hennessey's HP1000 kit boosts output to 1000hp, more than most supercars, resulting in a drop in acceleration times - 60mph taking just 2.7 seconds and reaching a maximum of 202mph before losing the fight against aerodynamics.
9 Shelby Cobra Super Snake - 800hp
Carroll Shelby, the genius behind the legendary Cobra name, was a former racing driver turned car designer and creator of one of the fastest road cars ever produced. Just two examples of the Cobra Super Snake were produced, one of which belonged to Carroll Shelby himself, used as his personal transport.
Weighing less than 2850lbs and built around the already powerful Ford 427 V8, Super Snake models were uprated with twin superchargers that more than doubled the output to 800hp. In the right conditions, it's capable of hitting 60mph in 4 seconds, flat out exceeding 200mph.
8 Speedkore Dodge Demon Turbo - 1400hp
Craving more horsepower is proving to be highly addictive and should carry health warnings. Challenger Demon SRT's are already able to rearrange internal organs, but this modified example boasts 1400hp. Externally showing little in the way of power upgrades, other than the carbon body it wears in the pursuit of weight saving, pop the hood and it's a different story.
Ditching the supercharger in favor of a twin-turbocharger setup, otherwise remaining a stock 6.2-liter V8 engine, Speedkores efforts paying off with setting a quarter-mile time of 8.77 seconds.
7 Callaway Corvette Sledgehammer - 898hp
Popular belief has it that Veyron was the first production car to exceed 250mph, but in fact, Reeves Callaway beat them to it in 1988, setting a record of 254.7mph with the Corvette Sledgehammer. Essentially a standard 6-liter V8 C4 Corvette with two turbochargers bolted on for good measure, total output climbed to 898hp.
Despite its impressive performance, the Sledgehammer has never officially been recognized for its achievement, the title at the time residing with Ferrari's F40 at 202mph, regardless, Callaway's turbo conversions increased in popularity. Sledgehammer remains a one-off project a reminder of what could be achieved with normal road cars.
6 Shelby Mustang 1000
Where Ford created the Mustang, Shelby American deserves all the credit for turning the model into the success it is today, by far the most reputable Mustang tuner around. No prizes for guessing Shelby Mustang 1000 produces 1000hp, replacing the standard engine with a modified GT350 5.2-liter unit complete with Whipple supercharger, modified ECU, and uprated transmission.
Requiring extensive bodywork changes to accommodate larger wheels, tires, and supercharger restricts suitable donor cars, Shelby offers the 1000 kit as a retrofit package to any post-2015 Mustang.
5 Hennessy Venom Viper SRT - 1000hp
For most gearheads, the Dodge Viper is all the muscle can anyone would need. A monstrously large 8.3-liter V10 engine produces 493hp in a simple rear-drive platform with little in the way of traction control other than the driver's right foot.
Factory spec cars already baing a handful didn't stop Hennessey Performance. A minor bump in displacement to 8.55 liters and a brace of Garrett turbochargers, adjustable traction control, and updated coil-overs resulted in the Venom Viper 1000. With double the power of the original, the Venom could reach 60mph in 3.25 seconds, going on to its maximum of 215mph.
4 Timeless Kustoms 1965 Mustang - 1000hp
Under normal circumstances, modifying a classic 1965 Mustang Fastback might seem like blasphemy, but Timeless Kustoms' efforts make a (mostly) convincing argument for the changes. Claiming to produce 1000hp from twin-turbocharged and supercharged Ford 5.2-liter V8 is no mean feat, with almost 4-time the power of the original 289 spec cars, it should be no surprise that this Mustang is quick.
We get why someone would want more power and custom bodywork, but the interior might not appeal to every gearhead... and then there is the price. Customers will need a donor car and a cool $1 million to get one of these.
3 Lingenfelter C7 Z06 - 1100hp
Corvette Z06 models with LT4 series small block engines are a popular choice among tuners as their robust design leave plenty of scope for huge power gains. LPE (Lingenfelter) has built some insane cars and has a long history of tuning Corvettes, their latest offering providing just how much power can be unlocked from the standard block.
Bespoke crankshaft, heads, fuel system along with uprated supercharger resulting in a sizable gain in power to 1100hp running on E85 gasoline. Available as a factory fit upgrade taking around 8 weeks to complete.
2 Blackdog Performance Camaro ZL11 - 1300hp
Designed to run on exotic fuels to achieve its headlining 1300hp, Blackdog's ZL11 Camaro is the most extreme example of modern American muscle cars. Featured upgrades list reads like an action movie script, twin-turbochargers, Weapon X fuel system, Monster clutch, all giving a clue to how far its creators have gone.
Recently offered for sale with no performance figures listed, however, Blackdog does promise owners can achieve 1111hp at the wheels when running on E55 gasoline, for daily use on regular E93, 815hp is more realistic.
1 Heffner Ford GT 975-2000hp.
With used prices hovering around $400,000 for decent examples, Ford GTs aren't exactly cheap to begin with, nor are they slow. For those with deep pockets and craving for more power, Heffner Performance has just the thing. Entry-level Stage 1 will set owners back $42,000, for which they get 975hp from a twin-turbo conversion along with custom titanium exhausts.
But this is just the start, Elite/Race upgrades have the potential to unleash 2000hp and propel the GT to 250mph requiring a full re-build of the drivetrain, pricing available on request subject to requirements.