The 924 Carrera GT uses a turbocharged version of the 924's 1984cc engine with an intercooler. A normally aspirated 924 makes 125bhp,
the type 931 turbo 175bhp, and the addition of an intercooler brings the 924 Carrera GT up to 210bhp. Apart from lighter pistons, most of the engine
internals are common to the Porsche 924 Turbo, which itself shares the majority of its parts with the 924.
911 parts were also used on the 937 that were not used on the 924 or 931: The 924 Carrera GT's 210 BHP goes through a 911 clutch plate,
the transaxle is strengthened using 911 syncromesh rings, and the Fuchs wheels are lifted from the 911 SC (front) /930 (rear). The brakes and the Koni front dampers are shared with the later 944.
Externally the 924 Carrera GT is similar to a 931, but with wider polyurethane wings at the front and rear, and a polyurethane hood scoop. These, slightly
lowered suspension, and the Fuchs alloys give the 924 Carrera GT a much more purposeful stance than a standard 924 or a 931. Inside the cabin the 924 Carrera GT
is surprisingly comfortable, with electric mirrors and windows as standard, and A/C and a large lift out sunroof (UK models only) as options.
Only red, black, and silver 924 Carrera GTs were made, the 924 Carrera GTS was only available in red. The styling exercise and full race cars were white.
Power BHP | Kerbweight | BHP per tonne | KG per BHP | Year | |
924 Carrera GTS CS | 270 | 1,060 | 255 | 3.9 | 1981 |
930 3.3 | 300 | 1,300 | 231 | 4.3 | 1981 |
924 Carrera GTS | 245 | 1,121 | 219 | 4.6 | 1981 |
944 Turbo S | 247 | 1,280 | 193 | 5.2 | 1985 |
911 3.2 Carrera | 231 | 1,210 | 191 | 5.2 | 1985 |
968 Club Sport | 240 | 1,320 | 182 | 5.5 | 1995 |
924 Carrera GT | 210 | 1,180 | 178 | 5.6 | 1981 |
911 SC | 204 | 1,160 | 176 | 5.7 | 1981 |
944 Turbo | 220 | 1,280 | 172 | 5.8 | 1985 |
944 | 163 | 1,210 | 135 | 7.4 | 1985 |
The 924 Carrera GT's engine is designated M31.50 with engine numbers beginning 3150. It generates 210 bhp at 6,000 rpm, or 105.8 bhp per litre, at a low 8.0:1 compression and was apparently the most fuel efficient
engine in the 924 range.
The M31.50 uses the standard 1984cc cast-iron Porsche 924 block and uprated parts as used on the M31.30 Series II 931, such as the aluminium head, camshaft, and cooling system.
There are few parts unique to the 924 Carrera GT, namely the lighter forged pistons made by Kolbenschmidt, a slightly larger version of the 931 KKK turbocharger running at 0.75 bar,
and a unique - although still similar to the European Series II 924 Turbo unit - Digital Ignition Timing Computer (DITC). Total dry engine weight is 175kg including the turbo and intercooler.
Manufacturer | Porsche # | Manf. ref | Figures | |
Pistons | (KS) Kolbenschmidt | 931 103 042 01 | 86.50mm, 8:1 compression | |
DITC | Siemens | 937 602 071 00 | ||
Turbocharger | KKK | 931 123 002 10 | K26-2660 GA 6.10 | Compressor cover 5326 100 5104 |
Compressor wheel 5326 100 6328 | ||||
Compressor exducer 66mm | ||||
Compressor inducer 39.6mm | ||||
Trim 36 | ||||
Intercooler | Langerer & Reich | 931 110 033 04 | 37091207, 68652 |
Getrag produced the G31 gearbox for the 924 Turbo, and it is perhaps
the strongest in the Porsche 924-944 range, much of which used an Audi-derived 016 transaxle. The G31 uses a number of parts from the 915 and 930 transmissions such as the baulk ring synchromesh
and bearings.
The 924 Carrera GT gearbox is designated G31.03, serial numbers start 3103. It is similar to the 931 unit, with the same ratios, but has strengthened gear sets to handle the increased horsepower.
A limited slip differential was an option on all G31 equipped cars. Like many racing gearboxes the G31 has a "dogleg" first gear; down and to the left, to reduce the risk of accidentally engaging first at speed. Second is where first would be on a normal H pattern box, third is where
second is, etc, etc. Reverse is above first. The ratios for the G31.03 are incorrect in the Technical Specifications book that is circulating on the internet. These are correct (thanks Pete).
G31.03 | 1st | 2nd | 3rd | 4th | 5th | Final |
Tooth count | 12/38 | 18/32 | 23/28 | 29/27 | 34/24 | 8/33 |
Ratio | 3.167 | 1.778 | 1.217 | 0.931 | 0.706 | 4.125 |
Max MPH* | 32 | 54 | 79 | 104 | 157 | |
RPM @ upshift | 3,542 | 4,118 | 4,555 | 3,955 |
*Assuming 225/50/16 rear tyres and upshift at 6,000RPM.
All Porsche 924s have MacPherson struts and coil springs at the front, trailing arms with torsion bars at the rear. The 924 Carrera GT has a lightly uprated version of the Series II Turbo suspension with strengthened rear trailing arms. Springs are from the pre-1980 924, which have a lowering effect on the 937. Porsche, Koni, and Bilstein dampers were specified as original equipment and are interchangeable with the 944. Koni and Bilstein dampers are widely available and are highly recommended as replacements. Double-check compatibility with front struts before buying. Either 21mm or 23mm front anti-roll bars could be specified, a 16mm anti-roll bar is fitted at the rear.
Damper brand | Front ref | Porsche # | Rear ref | Porsche # |
Porsche | 944 343 031 12 | 477 513 031 H | ||
Koni | 86-1980 | 944 343 031 11 | 80-2349 | 944 333 031 00 |
Koni adjustable | 8641-1038 Sport | 26-1209 Sport | ||
Bilstein B6 Sport | P30-0040 (Boge struts) | 477 412 059 A | B36-0161 | 477 513 031 A |
Bilstein B6 Sport | P30-0104 | 944 343 059 00 |
From the manufacturer's handbook. Camber, toe and caster are explained here.
Front | Rear | Notes | Notes II | |
Camber | -20' ±15' | -25' ±30' | ||
Toe | 0° +5' -15' | 0° ±10' | Toe angle difference | At 20° Lock: -1° ±20' |
Caster | 2° +45' ±30' |
The 924 Carrera GT wore Fuchs alloys from the 911 Carrera:
Size | Porsche # | Tyres | Shared with | |
Fuchs Front | 7Jx15 ET23.3 | 911 361 020 41 | 215/60 VR15 (2.0 bar, 29 psi) | 911 SC |
Fuchs Front (option) | 7Jx16 ET23.3 | 911 362 115 00 | 205/55 VR16 (2.0 bar, 29 psi) | 911 SC |
Fuchs Rear | 8Jx16 ET10.6 | 911 362 117 00 | 225/50 VR16 (2.5 bar, 36 psi) | 930 |
Both types of front wheel have ET23.3mm offsets, the rears have ET10.6mm (note the PDF incorrectly gives the offset as 23.3mm on the rear). All have five nuts with 130 PC diameter, the same specifications can be found on certain 911, 930, and 944 wheels.
Spacers on the rear wheels further widen the track.
The 924 and 931 had 6x14-16 inch wide wheels with ET20 offsets, giving them a narrower track and therefore
incompatible as a direct swap onto a 924 Carrera GT. Conversely, the 911 wheels used on the GT are unlikely to fit on
an unmodified 924 or 924 Turbo; the wider front and rear wings are required to accomodate them. When buying wheels, note that offset can be increased by using spacers, but cannot be decreased withou modifying the wheel.
The 924 Carrera GT uses the same floating calipers as the 924 Turbo and were carried forward to the 1982-5 944. Discs and pads are as per the 924 Turbo and 1982-5 944. The GT also has plastic vents that duct cool air from the front bumper to the discs.
Below are recommendations from the manufacturer's handbook from 1981. I have added information garnered from internet based research, so all recommended oils are the synthetic variants.
Service quantity | Type | Type II | Notes | |
Fuel | 98 RON (Super Unleaded) | 93 RON in USA | ||
Synthetic Oil* | 5.0l | 15-40W (road) | 20-50W (track) | Use 15-40W if < -15°C |
Cooling system | 5.6l (change) | 40% Anti-freeze | 50% if <30° C | Use aluminium compatible fluid |
Gear oil | 2.5l | GL-5 Hypoid gear oil | ||
Brake fluid | 0.2l | Glycol based DOT 4 | ||
Washer fluid | 6.0l |
Engine oil
*Older turbocharged engines usually require a high viscosity oil. Oil companies recommend using a synthetic oil of the originally recommended viscosity as listed above. The handbook recommends changing the oil every 10,000 Kms (6,000 miles). Oil consumption is listed as 1.5l per 1,000 Kms, but I have never found it to be that high.
My understanding of oil grades is that if you live in a cold (northern European) climate, use a lower first number in the multigrade scale (10-40W, 15-40W) to provide reduced viscosity (thickness) at low temperatures so that the oil can circulate easily and protect the engine. If you live in a hotter climate (southern European) the first number can be higher because the engine will rarely be started at freezing temperatures. If the engine is subject to track use and therefore the oil gets very hot, you need an oil that maintains viscosity at high temperatures, so the second number (15-50W) should be a minimum of 40W. 50W is probably preferred.
Gear oil
Like most Porsches and Ferraris, the 924 uses a transaxle (gears and differential in the same box at the rear of the car) which requires GL-5 gear oil, containing extreme pressure (EP) additives and antiwear additives to cope with the sliding action of hypoid bevel gears.
From Wikipedia on (API) GL-5 oils
API GL-5, oils for severe conditions. They contain up to 6.5% effective antiscuffing additives. The general application of oils in this class are for hypoid gears having significant displacement of axes. They are recommended as universal oils to all other units of mechanical transmission (except gearboxes). Oils in this class, which have special approval of vehicle manufacturers, can be used in synchronized manual gearboxes only. API GL-5 oils can be used in limited slip differentials if they correspond to the requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS.
Brake fluid
Brake fluid should be changed every 1-2 years. If the fluid is black in the reservoir, it definitely needs changing. Porsche originally recommended DOT (Department of Transport) 3 fluid, but DOT 4 superseded DOT 3 from about 2006. DOT 5 is a silicone based fluid mainly for use in racing applications and cannot normally be used in a system that has used a Glycol based fluid before it.
Below are recommendations from the manufacturer's handbook from 1981. I have added information garnered from internet based research, so all recommended oils are the synthetic variants.
Item | Specification |
Cylinders | 4 |
Cylinder block | Cast iron |
Cylinder head | Alloy |
Compression | 8.5:1 |
Bore | 86.50 mm |
Stroke | 84.40 mm |
Displacement | 1984 cm |
Valve operation | 8 valve, SOHC |
Firing order | 1-3-4-2 |
Fuel supply | Electric pump, K-Jetronic injection |
Spark plug | Bosch W3DP, Bosch W4CS, Champion N3G |
Spark plug gap | 0.6 mm to 0.7 mm (0.024" to 0.028") |
Ignition timing | 8° to 14° before TDC at 900 rpm |
Valve clearance (cold) | Intake 0.006" (0.15 mm), Exhaust 0.016" (0.40 mm) |
Valve clearance (warm) | Intake 0.008" (0.20 mm), Exhaust 0.018" (0.45 mm) |
The spark plug references listed in the handbook appear to be out of date for Bosch and Champion lists N2C (0E040) as the correct spark plug for the GT. I will update these references when I have spoken to Bosch. Find more information about spark plugs here.
Don't understand any of the technical terms used here? Car Bibles and Autozine are excellent encyclopedias of automotive technology.