Engines: 2.7-3.0-3.2 litres

Porsche introduced the 2.7 litre engines in 1973 with the Carrera RS 2.7 that never was officially imported into North America. The first and only versions we received in North America were the K-Jetronic-equipped (CIS) units due to increasingly stricter emissions regulations. This precluded using the excellent Bosch MFI system from the RS engines. The 1974 2.7's had no add-on emission equipment and used the early style 3-into-1 heat exchangers that gave these engines more power and lower operating temperatures than the later ones. The various 2.7 litre powerplants used in 75-76-77 were equipped with air pumps and later, thermal reactors that reduced engine life to less than half of the 74 2.7's. Almost all of these engines require extensive machine work to make them durable & reliable.

The magnesium engine cases used in the 2.7 were also subject to pulled head studs and main bearing bore distortion from excess heat. Cylinder heads warped and valve guides needed replacement within 50K miles. These 7R-series cases need very careful inspection by a competent machinist to determine the feasibility of reusing or replacement with a better one. Using a 7R case from a 2.4 litre engine may be preferable due to its less heat stress. The early-style 7R case found in the 2.4 litre engines must be machined to accept 90mm 2.7 litre cylinders.

1976 saw a change in the oil bypass system in the 7R case that should be incorporated into any rebuild of these engines. Replacing the oil bypass pistons and springs along with a case modification allows the use of the larger oil pumps from SC and Carrera engines. The largest oil pumps; Turbo and 964, require machine work to make room but these are the best pumps that Porsche used. Turbo pumps are aluminum instead of the magnesium used in the 3.6 pumps and these maintain better oil pressure when hot due to less thermal expansion.

In 1978, the aluminum-cased 3.0 SC engines were introduced using the Turbo case from the 76 930's. These have proven to be quite reliable from racing experience with the 934 and 935 Turbo cars. The European-only 76 Carrera 3.0 used this case as well and its quite understressed in most naturally-aspirated applications. The 3.2 litre engine used in the 84 Carrera has a slightly modified version of this engine case that is quite strong and requires minimum preparation for high-performance or racing use.

Here is a picture of a "Boattailed" engine case. This process involves machining, reshaping and polishing the main bearing webs between each cylinder to enhance airflow under the piston when its traveling downward. This modification is necessary for a racing engine to gain maximum power. 911 engines will see about a 10+ HP improvement above 7000 RPM from this modification.

Cylinder head differences between the 2.7-3.0-3.2 engines lie mainly in port and valve sizes. All of the 2.7 litre engines use 46mm intake valves and 40mm exhaust valves. 3.0 and 3.2 litre engines use 49mm intake valves and 41.5mm exhaust valves for improved breathing. Port sizes vary among the 3.0 SC engines. The 78-79 SC's had larger intake ports than the later 80-83 engines and are preferable for performance applications where stock heads must be used. High-compression applications (over 9.8:1) should use twin-ignition for best power and detonation resistance.

Camshafts use in the 2.7-3.0-3.2 powerplants were all quite similar due to restrictions and limitations imposed by the K-Jetronic systems and emission regulations. CIS-equipped 2.7's can benefit from using the SC-grind cam in these engine due to the increased lift. Since Porsche changed the cam tower design to a 4-bearing setup with the 3.0 engines, SC cams will not fit the 2.7 litre engines; you must either have your 3-bearing cams reground with this profile or install the later 4-bearing cam tower with SC cams.

Carbureted or MFI-equipped applications will, of course, require different cam profiles for best power and torque. Good choices are the Factory "S" cam, the GE-60,121/149, and GE-80 for high compression, large displacement engines.

Emission regulations and testing have made induction choices for these engines somewhat tricky. Certainly installing a pair of Weber or PMO carburetors with the proper venturi's and jetting will result in substantial power and throttle response increases. Mechanical fuel injection for the 2.7-3.0-3.2 series ranges from the bolt-on variety to a good degree of custom (expensive) work. The MFI system from the Carrera RS 2.7 used the 2.4S throttles and stacks with an "S" pump and the RS internal space-cam. This system, albeit expensive to reproduce these days, works very well. A less expensive alternative is a set of PMO carburetors on tall manifolds. Other options are Electromotive's TEC-II EFI and aftermarket EFI throttle bodies. This system has excellent power potential once its programmed.

For a stock 2.7-3.0-3.2 that must retain the OEM induction, there are limitations imposed by the FI that prevent the use of larger cams than SC-C2 grinds. CIS-engines can be upgraded with displacement increases and Carrera engines can be improved with a different Motronic Chip and muffler change. 3.2 Carrera's also respond to some intake manifold modifications due to the uneven airflow characteristics of the OEM manifolds. The stock Carrera's intake manifold runners are well known for unequal airflow and there are some great gains to be made here that translate into more power, greater smoothness and better drivability from each cylinder receiving the same quantity of air and fuel.

Airflow comparisons from 3.2 Carrera Stock vs Flowed Intake Manifolds

Other changes such as Mass-Airflow sensors and oversize throttle bodies are more expensive and the cost-per-HP increases from these bolt-on's may not be cost effective for some people.

The 75-on 2.7 and 3.0-3.2 litre engines also benefit from the installation of the 74-style exhaust system. Using a pair of SSI heat exchangers and a dual-inlet muffler generally will net you 12-18 HP on the larger engines and 10-12 HP on the 2.7's. These are slightly small for 3.2 litre engines but better than any OEM system. This is illegal to do on catalyst-equipped and you may need to re-install the OEM system for local emissions testing and compliance.

Take a look at this aluminum-cased 2.7 built for Porsche Club racing with MFI, twin-ignition, lots of compression and over 290 HP.

Here are a few well-proven Performance configurations for the 2.7-3.0-3.2 litre engines

  Here are some pictures of Porsche heads showing a stock port and the ported version. Its quite a job to do these and make each port flow the same as the others at all valve lift openings. This is the main key to making power since any internal combustion engine is merely an air pump.

Compare the rough surface of this stock port . . . 

. . with this magnificently smoothed port 

. . . or this one.

As you can see, there are quite a few variables to consider and play with when contemplating an engine performance increase. Cat-back exhaust systems involve the installation of an aftermarket muffler behind the OEM catalytic converter. Installing a good quality performance chip will net about 7%, mostly in the mid-range. This narrows the detonation margin and requires premium fuel.

Installing Twin-ignition on the 3.0 and 3.2 engines requires either a converted single distributor, a 3.6 dual-distributor with modified internal pickups or a pair of Electromotive HPV-1's. This is not inexpensive to do but is quite necessary on any of these big-bore engines with compression ratio's at 9.8:1 or higher. Failure to do so can result in broken rings from detonation. See the "Let's Talk about Porsches" page: http://www.rennsportsystems.com/2a.html for further information about fuel and detonation difficulties that cannot be easily detected.

Since engine modifications are done on an individual basis, contact Rennsport Systems for further information

E-mail: info@rennsportsystems.com

503.244.0990