Twin turbochargers returned, but their intercoolers now nestled low in the rear fenders, behind the wheels, ingesting through a trio of 959-type slots. The engine gulped air through a vertical duct high on each rear fender. Up front was a modestly enlongated nose with two large outboard intakes for cooling the brakes and a wide central opening for the engine radiator and a separate oil cooler.
Despite all the ductwork, plus compression bumped from 8.0 to 9.4:1, the 996 Turbo was only a bit more muscular than the 993 model it replaced. Horsepower climbed by 15 to 415 at 6,000 rpm, while torque swelled by 13 pound-feet to 413. However, that torque spread over a broader range of 2,700-4,600 rpm.
Boost pressure was raised to 9.4 psi, with bursts of up to 11.4 psi available when allowed by the Bosch Motoronic ME 7.8 engine computer. Also notable, the G96 engine was "greener," rating U.S. Low-Emission-Vehicle status at a time when many lesser cars did not.
from:
http://auto.howstuffworks.com/porsche-911-history39.htm