Jaguar’s forthcoming XFR has validated itself with an almighty 363km/h top end run at the Bonneville Salt Flats. As a publicity primer for the public unveiling of the XFR this week at the Detroit auto show, Jaguar commissioned Paul Gentilizzi’s Rocketsports (famous for its IMSA racing team of yore) to shatter Jaguar’s own top speed record.Quicker than the XJ220 on standard tyres?The Rocketsports team liberated extra power from the engine, added some ballast for grip and aerodynamics for stability.During a secret high speed run in Northern Utah, with Gentilizzi himself behind the wheel, the XFR managed a crushing 363km/h speed on its ninth run – obliterating the Jaguar record of 349km/h, previously set by the XJ220 supercar in 1992. Though the ECU was essentially rechipped to super-polluting parameters and the intake/exhaust system modified (upping power from 375kW to 441kW) the 5-litre supercharged V8 engine was a standard unit with original internals. Even more astounding was the standard active Dana rear differential and gearbox, which ran with untouched gear ratios – the ability to cope with 363km/h drivetrain friction and operating temperatures are as apt a performance endurance test as possible. Tyres for the top speed run were stock too, a set of Michelin Pilot Sport 2s inflated to 3.4 bar to help minimize drag on the relatively soft salt surface, which hinders outright speeds nearly as much as power sapping 1280m altitude of Bonneville. Gentilizzi’s technical team noted the XFR was recording 6% wheel slippage at the top end, despite the additional rear spoiler fitted to reduce drag and 113kg of ballast riding along in the boot. Jaguar would obviously never encourage potential XFR owners to try and match the Rocketsports team’s nearly suicidal speeds; but the 363km/h proven run is a nice-to-know fact in a world of AMG, RS and M-division pub banter.