from;
http://www.clarks-garage.com/951faq.htm#models
In 1988½ Porsche introduced a new 944 Turbo which was designated as a 944 Turbo S. The first example of the 944 Turbo S were a limited production run. Exact numbers on the limited production 951 S cars varies, but seem to be between 750 and 1000. All of the limited production vehicles came with a Silver Rose Metallic exterior and burgundy plaid cloth interior.
The Turbo S received the M 44.52 engine as opposed to the M 44.51 engine of the earlier models. The engine itself remained essentially unchanged from the early 1988 models. However, the turbocharger was changed to a K-26#8. The Turbo S was electronically limited to the same maximum boost (1.75 bar) as the early 944 Turbos. Also both models achieve maximum boost at approximately 3000 rpm. However, the K-26#8 turbocharger was capable of maintaining maximum boost until 5800 rpm while the boost on the early turbos would decrease from 1.75 bar at 3000 rpm to 1.52 bar at 5800 rpm. This resulted in a 30 hp increase in peak horsepower and a 15 ft-lb. Increase in peak torque.
The Turbo S transaxle came standard with a limited slip differential. However, there were improvements to the differential over previous models. The Turbo S differentials have inner plates which are 2.5 mm thick as opposed to 2.0 mm on earlier models. This required the two differential thrust rings to be made 0.5 mm thinner for the same overall thickness. Also, the inner plate and differential shafts are molybdenum coated for additional hardness. The clutch had a two-stage torsional spring damper with the friction material being bonded and riveted to the clutch disc instead of just rivets on earlier models.
The wheels on the Turbos were milled forged 7J x 16 in front and 9J x 16 in the rear (52.3 mm offset). The tires were 225/50 VR 16s in front and 245/45 VR 16s in the rear. The M 030 suspension package was standard equipment on the Turbo S models as well as ABS.
With the M030 option, height adjustable Koni yellow struts were added. Also with the M030 option, the strut bearings have a harder rubber compound than earlier models which can be identified by a green stripe on the underside of the bearing. The spring rate for all 944 Turbos not equipped with the M030 option is 21.8 N/mm with an unsprung length of 251 mm (through the end of the '88 MY). The M030 option springs have a rate of 28 N/mm with an unsprung length of 220 mm.
With the M030 option, the Koni yellow shock absorbers will have two white dots offset by 180°. Also with the M030 option, the torsion bar size was increased to 25.5 mm.