The ST4s used the liquid-cooled Desmoquattro (four desmodromic valves) engine based on the Ducati 996. The Desmoquattro was largely unchanged from the 996 Super-Bike, and retained a valve angle of 40°, but lost 4 mm of diameter on each of the intake throttle bodies (down from 54 mm on the 996). Chassis clearances also required the use of the more compact cylinder head design that was shared with the 748 Super-Bike and Monster S4.
In spite of the smaller intakes, the ST4s actually made slightly more power and torque than the 996 Super-Bike due to the mostly straight-through design of the ST's exhaust, compared to the under-seat exhaust of the Super-Bike.
Spesifications :
Layout: Transverse, liquid-cooled 90° L-twin, belt-driven DOHC, desmodromic 4V, 996 cc.
Bore x stroke: 98.0 × 66.0 mm (3.86 × 2.60 in).
Compression ratio: 11.5:1.
Power (Ducati changed to using an inertial dynamometer, from a brake version, to rate power and torque in 2005. However, the engine remained unchanged):
2002-2004: 86 kW (115 hp) at 8,750 rpm.
2005 only: 89.1 kW (119 hp) at 8,750 rpm.
Torque:
2002-2004: 98 N·m (72.3 lb·ft) at 7,000 rpm.
2005 only: 102.9 N·m (75.9 lb·ft) at 7,250 rpm.
Maximum engine speed (electronically limited): 10,000 rpm.
Induction: Marelli electronic fuel-injection with two 50 mm throttle bodies.
Ignition: Electronic, single centrally-positioned spark plug per cylinder.
Starting: Electric with anti-theft immobiliser, using a chip embedded in the key.