The latest evolution of the Mustang is marked by im- provements in design, powertrain, and handling. These include significant improvements for its V6 and V8 engines, with increased power and torque and improved smoothness and refinement. However, Ford engineers have achieved these substantial power gains while maintaining fuel economy levels. In addition, the California version of the 3.8-L split-port-induction (SPI) V6 now meets Low Emission Vehicle (LEV) requirements, while the California version of the 4.6-L SOHC V8 meets less-stringent Transitional Low Emission Vehicle (TLEV) standards.

The power produced by the V6 engine is up more than 25%. It is rated at 142 kW (190 hp) at 5250 rpm, a gain of 30 kW (40 hp). Torque is 298 N•m (220 lb•ft) at 2750 rpm, 7 N•m (5 lb•ft) more than its predecessor.

Ford says that the biggest contributors to the power increase are improved engine breathing, achieved with a new intake manifold that has two runners per cylinder, and flow improvements in the cylinder head. Further gains are made possible by a new, high-tech piston coating that reduces friction.

1999 Mustang Engine Specifications

3.8-L 4.6-L GT 4.6-L SVT Cobra Engine type 90o OHV V6 90o SOHC V8 90o DOHC V8 Valves per cylinder 2 4 Block Cast iron Aluminum (Iron cylinder liners) Head Aluminum Power 142 kW (190 hp) @ 5250 rpm 168 kW (225 hp) @ 4750 rpm 239 kW (320 hp) @6000 rpm Torque 271 N•m (200 lb•ft) @ 3000 rpm 393 N•m (290 lb•ft) @ 3500 rpm 427 N•m (315 lb•ft) @ 4750 rpm Bore x stroke 96.5 x 86.4 mm (3.8 x 3.4 in.) 91.4 x 91.4 mm (3.6 x 3.6 in.) Compression ratio 9.0:1 9.85:1

In addition to the power increases, a first-order balance shaft is employed, which helps smooth engine vibration. Stiffening ribs have been added to the front and rear faces of the block to reduce vibration and noise. Long-term durability is improved with new main and thrust bearings.

The output of the Mustang GT's SOHC V8 engine is 26 kW (35 hp) greater for 1999, with a rating of 194 kW (260 hp) at 5250 rpm. Torque is up by 14 N•m (10 lb•ft), to 409 (302) at 4000 rpm. The top of the Mustang range, the SVT Cobra, gets an uprated DOHC 4.6-L V8 for 1999. The engine is expected to produce about 239 kW (320 hp) at 6000 rpm and 427 N•m (315 lb•ft) of torque at 4750 rpm — increases of 11 kW (15 hp) and 20 kW (15 lb•ft).

The power gains on the SOHC unit come from new camshafts with higher lift and longer duration, as well as bigger valves and straighter intake manifold runners. All of these changes combine to increase airflow above 3000 rpm.

On the SOHC V8, the shape of the combustion chambers has been revised to provide improved tumbling motion of the air/fuel charge, and the exhaust valves have been repositioned.

This produces more complete burning of the fuel, which optimizes power and fuel economy, while reducing exhaust emissions. On the DOHC unit, new intake-port geometry and a similar combustion chamber design create a tumbling air/fuel charge. More precise control of detonation is made possible by the use of a new differential linear knock sensor, which replaces a resonant unit.

Both V8 engines feature a new coil-on-plug ignition system for 1999. This system provides a high-energy spark for improved burn characteristics and is more reliable than single-coil systems. Additionally, improvements made to the V8s for greater durability include new aluminum upper main, upper thrust, and rod bearings.

The fuel-delivery system on all 1999 Mustangs is a new, returnless design that incorporates a variable high-pressure fuel pump with the fuel-injection system. The fuel pump has its own microprocessor, linked to the powertrain control module, which determines required fuel flow based on demand and temperature variables. This system reduces the amount of fuel-tank vapor compared with systems that have a return line. Fuel-tank vapor is further reduced with a new onboard refueling vapor recovery system that is required for 1999.