That’s because Hennessey’s HPE700 package brings around 700 horsepower to the table. For the Corvette Stingray, Hennessey offers its HPE700 package with either a supercharger or a twin-turbocharger setup. The latter produces 708 horsepower at 6,300 rpm, which is considerably more than even the new supercharged Corvette Z06's output.
This video shows a HPE700 twin-turbocharged Corvette Stingray strapped to a dyno. With a mild 7 psi of boost and regular 93 octane fuel, this tuned ‘Vette pumps out 608 horsepower to the rear wheels. Given even a conservative drivetrain loss of 15-20 percent, it's clear Hennessey is more than meeting its performance claims.
Modifications necessary to ascertain these stratospheric performance levels include a custom twin-turbocharger setup, a fuel system upgrade, new intake and exhaust systems, and retuning of the ECU.
You can see some of Hennessey’s other upgrades for the Corvette Stingray in the links below: