The TT means twin turbo. Right ‚ÄĒ dual turbines atop the Lamborghini Murci√©lago's already potent quad-cam V12. It's the handiwork of Doug Levin Motorsports, best known as a fitter of superchargers for the Dodge Viper. One poster on Lamborghini Talk says the tuner Lambo has the mannerisms and driveability of a regular Murci√©lago, and then boost kicks in:

Lag is basically non existent. The Murci is a quick revving car as it is. The car makes 800hp at the motor. It feels like more than that if you can imagine it. I have been in a Murcie Roadster under hard acceleration, and this feels 2 times as fast under boost. The car will spin all 4 wheels all through 1st, and I would imagine part of second gear. The blowoff valve noise under hard accelleration is louder than any Supra I have heard. Especially in a open topped Roadster. I have to imagine that when he was on it, it must have been an almost scary situation to be next to the car.

Check, please. [via Lamborghini Talk]