Air-cooled flat six development

Introduction of the 2ltr (1991cc) 911 with engine type 901/01. Sand cast engine casings, heads, camshaft housings etc. Centre feed camshafts later replaced with the spray bar lubrication as we know today. Solex carburettors were used. Engine produced 130bhp @ 6100rpm 128lb/ft @ 4200rpm. Lightweight clutch cover used with Bronze sintered surface.

Introduction of the 901/05 engine Solex carburettors replaced by Webers. Bhp and max toque valves remain unchanged from the earlier 901/01 engine. During 67 model year the forged rocker arms were replaced by cast-iron items and three more holes drilled in the spray bays to spray oil up towards the inlet rocker arms. From 67 rocker shaft pinch bolts changed to 7mm.

Introduction of the 901/02 engine. With the experience from racing, Porsche pushed the bhp up to 160 @ 6600rpm and torque up to 132lb/ft @ 5200rpm. This was achieved by modified cam timing, higher compression ratio, larger ports and valves. The exhaust benefited from equal length 3:1 heat exchangers. Other updates from 68 included, rubber chain guides replacing the early aluminium and rubber items used until 67. The chain tensioners were updated so they had a sealed reservoir instead of an open reservoir as used on the early engines. The change over to the use of high pressure Magnesium casings began with valve covers, chain casings, chain covers and the top breather housing. At the same time they increased the number of lower rocker cover mounting studs from six to eleven. In the spring of 68 they started to cast the engine casings in Magnesium (22 pounds lighter against the Aluminium one). This was at the time the largest item pressure cast in Magnesium. At this time they also improved the layshaft end float by using flanged bearings instead of plain bearings.

Mechanical fuel injection (MFI) introduced. This helped Porsche meet USA emission standards. The S (type 901/10) now produced 170 bhp @ 6500rpm and max torque 134lb/ft @ 5500rpm. This was achieved with slightly higher compression ratio, larger valves (same as the 906) and of course MFI. The clutch cover plate surface was changed as the Bronze did not have a very long service life. 1969 T moved over to dual valve springs. Capacitor discharge ignition (CDI) standard on E and S versions. They offered an upgrade kit for T owners. The S models came with an additional oil cooler mounted to the front right wheel housing.

Capacity increase to 2.2ltr (2195cc) The cylinder heads all came with inlet valves 46mm and exhaust 40mm and only the port sizes were changed for the different models. An improved combustion chamber shape was introduced to eliminate the detonation problems. The layshaft now benefited from bearings being fitted to the inner end instead of running it the case.  Rockers arms changed, still cast-iron but now fitted with a Bronze bushing. Larger clutch friction plate used 215mm upped to 225mm. They moved over to a pull clutch instead of a push clutch. The cylinder to head joint now included a sealing ring (CE ring). Re-designed con rod with longer bolts. The S Type 911/02 now had 180 bhp @ 6500rpm max torque 147lb/ft @ 5200rpm.

Small changes only. Oil squirter’s fitted to the crankcase to aid piston cooling, they reduced piston temp by 50 deg C.

Capacity increased again to 2.4ltr (2341cc). This was done by altering the stroke of the engine. The width of the big end bearing was increased as the diameter was decreased thus retaining a similar bearing surface area. The biral cylinders from the 2.2 were retained. All engines now fitted with forged crankshafts. The input shaft was increased in size from the WV 13/16 24 splines to 7/8 20 splines. The S version type 911/53 increased in power to 190 bhp @ 6500rpm with max torque 158lb/ft @ 4000rpm.

The T version (US) was equipped with Bosch K-jetronic fuel injection (CIS) to combat lower emission levels. Introduction of the iconic 2.7 (2684cc) Carrera RS (type 911/83). This was the first production engine to receive Nikasil cylinders. The crankcase received reinforcement to the rear and around the main bearing cylinder area. This engine was identical to the S version except for the cylinders and a different space cam fitted to the MFI pump. This pushed the output to 210 bhp @ 6300rpm and raised torque to 188.4lb/ft @ 5100rpm. An RSR version (type 911/72) 2.8ltr (2808cc) produced 308 bhp @ 8000rpm torque 217ib/ft @ 6200rpm. The RSR engine had a lot of non standard special parts, required to get the power increases.

The US market at this time had only two engine options due to the increasing pressure to meet emission levels (both with CIS). 3.0ltr Carrera introduced (type 911/77 not for US). These had MFI and produced 230 bhp @ 6200rpm and 203lb/ft of torque @ 5000rpm. Revised external oil cooling system with built in bypass valve.

The US market cars were fitted with air injection to meet emissions. Due to noise pollution laws in Europe, the exhaust system was updated and now incorporated a side silencer as well as the existing rear silencer (but with only one inlet instead of two). 930 Turbo introduced (type 930/50 with CIS). This engine featured the new aluminium-silicone alloy casing. The head studs were changed for the turbo to Dilavar. Valve sizes increased to inlet 49mm and exhaust 41.5mm. Breaker-less CDI was also introduced with the turbo. New plastic chain guides and improved chain tensioner’s introduced. The clutch was increased in size to handle the power from 225mm to 240mm. The gearbox input shaft was also increased in diameter. Porsche increased the fan speed to help with the cooling. The turbo produced 260 bhp @ 5900rpm and 253lb/ft @ 4000rpm.

The US still had the under powered engines. The fan was changed to a 5 blade instead of an 11 blade and the fan speed increased to increase charging whilst reducing noise level. All engines used four bearing cam carriers apart from engines were the type number starts 911/-. Oil pumps changed and the bypass system in all engines. The pressure side of the pump was increased and the scavenge was reduced. The bypass was redirected to the pressure side of the pump to reduce the amount of work the scavenge pump needed to do.

Later this year Dilavar studs were fitted to the bottom row of head studs. Chain casings & covers and valve covers changed to pressure-cast aluminium-silicon alloy. In March of this year they modified the middle barrel defectors to promote better cooling.

Introduction of 3.0ltr SC (2994cc) type 930/03 180bhp @ 5500rpm & 165lb/ft @ 4200rpm. All engines were fitted with air injection pumps. Rubber damper fitted to centre of clutch plate to reduce transmission noise (proved inadequate and service life was reduced). New crankshafts with larger main bearing journals. Flywheel received new mounting with 9 bolts instead of 6. The rear main seal was increased at the same time. The chain guides were updated, the brown ramps were replaced by black ramps, which are higher apart from the bottom R/H one in the engine. This remained as before (brown in colour). 3.3ltr (3299cc) turbo introduced with larger piston pins 23mm instead of the normal 22mm. Head sealing rings stopped being used. The cylinder cooling fins were redesigned to promote even cooling to the cylinder. Oil pumps redesigned and pressure and scavenge were both increased in size. Inter coolers added to turbo charged cars.

 Unchanged

Oil pump fitted with a cylindrical filter and had a suction venturi. This was fitted to eliminate oil scavenge problems found with sustained high engine rpm. Lower valve covers had the addition of extra ribs to try and stop warping and oil leaks. Revised spigot bearing set up. Increase in compression ratio for SC engine giving an extra 8bhp and 10lb/ft of torque. Revised chain idler arms, wider for support, fitted with bronze bushings. After January of this year turbo engines were deleted for the US and Canada markets.

Revised air box to solve backing and blowing the air box apart. Return of the turbo for Canadian market. Increase in power for the SC engine type 930/10 to 204 bhp @ 5900rpm 189lb/ft of torque @ 4200rpm.

Revised camshaft gear retaining fixing (nut replaced by bolt). New alternators with built-in regulators instead of remotely mounted ones. 930 fitted with oil trap in the vent line to separate the fumes and return oil back to the oil tank. 

Improvements made to the turbo engines to improve emissions and general running. A new distributor was fitted to help emissions. Capsule added to the fuel distributor to enrich mixture when throttle opened suddenly. Separate muffler added to wastage turbo engines (to reduce noise). Revised crankcase without sump plate. This new crankcase came in late 1983.

Capacity increased to 3.2ltr (3164cc type 930/20). This was achieved by using a different crankshaft and con rods. This new engine had Bosch Motronic controlled fuel and ignition system. Pressure feed chain tensioner’s fitted. Similar exhaust system to the SC, but larger diameter pipes used. It produced 231 bhp @ 5900rpm and 209 lb/ft of torque @ 4800rpm. In July of this year Porsche upgraded the front oil cooler to a matrix type on 3.2 and turbo cars. Front bumper modified to aid air flow to oil cooler.

Unchanged

Turbo engine returns to US with emission equipment to meet the emission laws.

Porsche installed a temp switch to the front oil cooler to operate a cooling fan (US vehicles). New transmission G50 replaces 915 along with a 240mm clutch instead of the 225mm as used with the 915 gearbox.

Unchanged

 1989

Capacity upgrade to 3.6ltr (3600cc) type M64/01. This came with a big increase in power over the 3.2 Carrera engine, 250 bhp @ 6100rpm torque and 228lb/ft @ 4800rpm. This was the first production engine for road use with twin spark. This was equipped with a new larger oil pump with bushings at the ends of the shafts, before the shafts run in the oil pump outer housing. This engine does not run an engine oil cooler just an improved matrix oil cooler with temp controlled fan for cooling. Special ceramic liners were fitted to the exhaust ports to reduce the heat transfer to the head and aid cooling, at the same time the surface area of the cooling fins were increased again to aid cooling. Redesigned chain guides to reduce noise. They replaced the aluminium gear on the layshaft with a steel item which increased service life. This engine again, like the 3.2 Carrera, had a Motronic engine management system, but this time a knock sensor was used to protect the engine against pinking & detonation. The exhaust system was increased in size at the same time. The cylinder to head runs no sealing ring and the base gasket for the cylinder was deleted in favour of a rubber ‘O’ ring. The engine fan has two pulleys, the fan runs at a slower speed to reduce noise and the alternator at a higher speed to keep the charging rate high. Cam covers, chain case covers are fitted with rubber seals to try to solve oil leak problems. Piston squirters increased in size to 2mm.

Porsche added a dual mass flywheel and removed the rubber damper from the clutch plate. Piston updated to try to limit oil consumption.

During this model year the cylinder head leaking problem was addressed with the addition of a sealing ring. At the same time the mating surface cylinder to head was increased. Layshaft gear changed material from steel to cast-iron in an attempt to reduce noise. The inlet manifold was update to a black plastic one, this improved performance due to a smooth internal surface against the aluminium cast surface. Turbo version introduced similar to the 3.3 turbo. This engine, type M30/69, produced 320 bhp @ 5750rpm & torque was 332lb/ft @ 4500rpm. These engines used the later through bolt setup and cylinder base seal as the 964 engine, along with the larger 2mm piston squirters. Exhaust system carried over with the addition of a catalytic converter and silencer mounted on the R/H side. The engine had CIS, but the ignition was controlled by an ECU.

Introduction of the Carrera RS model type M64/03. This had a 10 bhp increase and 7.5lb/ft increase in peak torque. The flywheel was replaced by a lighter item (sports version). The fan belts were replaced by a single belt, so both alternator and fan ran at the same speed. The dme unit was modified to increase power. Engines factory filled with Synthetic oil from August this year. May of this year Porsche moved over to a LUK dual mass flywheel, which had a longer service life.  

Turbo 3.6ltr (3600cc) introduced type M64/50 360 bhp@5500rpm 383lb/ft @ 4500rpm. CIS was carried over from the 3.3ltr turbo. New camshafts, pistons, cylinder heads and bigger exhaust valves. The lower cam covers remain unchanged as they only ran one spark plug per cylinder. The exhaust system remained the same as the 3.3ltr turbo.

Introduction of the 993 Type M64/05 272 bhp @ 6100rpm torque 243lb/ft @ 5000rpm similar to the 964 engine with more power and better fuel consumption. Crankshaft stiffness was improved and this lead to the deletion of the crankshaft damper. Piston and piston pin weight reduced. Redesigned rocker shafts and rockers with built in hydraulic tensioners (inlet and exhaust rockers different unlike other engines which used the same rockers). Update management system with the air flap being replaced by a hot film unit. Improved exhaust system (back to the early manifold set up three into one).

Capacity increased for the Carrera RS model to 3.8ltrs (3746cc) type M64/20 300 bhp @ 6500rpm torque 261lb/ft @ 5400rpm. This was also fitted with the Varioram inlet system along with the main stream cars, which were still 3.6ltrs. The RS used new cylinder heads with large inlet valves. As before the RS used a lighter flywheel (sports version).

Twin turbo C4 introduced 3.6ltr (3600cc) M964/60 408 bhp @ 5700rpm torque 400lb/ft 45000rpm. Stronger con rods were designed. New cylinder heads with the ceramic liner in the exhaust port were used. Cooling fins on cylinders heads improved for better cooling. The exhaust system had separate catalytic converters and silencers for each bank. Motronic system also controlled the boost pressure.