all cars. Computer controlled 0-100% PSD locking differential added to both models. S4 no longer available with manual gearbox. Dual airbags now standard across all Porsche models in U.S. Driver's and front passenger airbag optional elsewhere, only driver's side bag available in RHD markets. 1991 Model designation: 928 S4 / 928 GT Engine displacement: 5.0 L Valves: Four per cylinder Power: 320 PS (316 hp, 235 kW) (S4) / 330 PS (326 hp, 243 kW) (GT) Changes: Improvements to cooling in exhaust side at cylinder heads, steering rack, power steering pump, soundproofing, front cooling flaps deleted, new style shift knob with integrated leather booth in manual gearbox cars, etc. Temperature sensors for ignition circuit monitor system moved from #4 and #8 cylinders to #3 and #7 cylinders to improve their efficiency. Check engine warning light added to all US models due to California regulatory demands. Two airbags as standard in LHD models during model year production for most markets. 1992 Model designation: 928 GTS Engine displacement: 5.4 L Valves: Four per cylinder Power: 350 PS (345 hp, 257 kW) Changes: Engine displacement increases to 5.4 L due to increased crankshaft stroke. Piston compression height adjusted to matched new stroke. 10.4:1 compression ratio pistons Milder camshafts for emission purposes Bodywork updated with flared rear fenders and so-called "cup" style wing mirrors. "Big Black" front brakes, significantly larger than the "S4" version. Stronger manual gearbox with differential driven oil pump and front-mounted oil cooler. GTS became available in North America at January 1992 as early 1993 model with later model year VIN. These cars use the same parts as 1992 models and can be differentiated from true 1993 US models with separate VIN sequences and option code M718. 1993 Model designation: 928 GTS Engine displacement: 5.4 L Valves: Four per cylinder Power: 350 PS (345 hp, 257 kW) Changes: Cylinder block lower half studs replaced with bolts. Engine piston rings changed to limit oil consumption and pistons changed to strengthen skirt area. Minor update to gearbox clutch. Air conditioner refrigerant changed to R-134a. Driver-side airbag standard in RHD cars, passenger-side airbag not available in them. 1994 Model designation: 928 GTS Engine displacement: 5.4 L Valves: Four per cylinder Power: 350 PS (345 hp, 257 kW) Changes: Cabin pollen filter added. Dynamic kickdown for automatic transmission models. Wheel design changed to "Cup II", RDK deleted at same time. First 19 US models were