Porsche 911 SC Carrera

This is the final installment in a series detailing the metamorphosis of a limping 3.2-liter 911 Carrera engine into a fire-breathing, 3.5-liter twin-plug monster motor. If you haven't followed along to this point, valve guides that are infamous for wearing prematurely on many SC and Carrera motors led to increased oil consumption and an intermittent cloud of blue smoke while at idle. Since the 911 was turning heads for all the wrong reasons (my wife was even embarrassed to ride in it), I had little choice but to bite the bullet and tear the motor down, all the while cursing the engineers in Stuttgart for my misfortune. Just as a Phoenix rises from the ashes, so did my grandiose dreams of power and torque from the depths of despair. I proceeded to select many of the finest components from the Porsche aftermarket for this engine build in an effort to not only substantially increase horsepower, but long-term reliability as well. The long-block is now complete; all that's left is the installation of the ignition, induction and exhaust systems. The big 3.5L should allow my 911 to go toe-to-toe with just about anyone, but we'll soon see if this motor has the knockout punch it is being built to deliver.

Intake, exhaust and electrical assembly

The first order of business on the ignition side of the motor was to fit the twin-plug 993 distributor as used on 1995-1997 models. This would also create the opportunity for measuring the approximate length needed for Magnecor's KV-85 spark plug wires that would have to be specially made for this application. I also carefully inserted the freshly powdercoated fan strap through the two slots in the engine case in preparation for the engine fan shroud, alternator and fan assembly. Steve Becker set the assembly into position and connected the alternator to the main engine harness while I installed the front engine mount carrier and crossmember, spark plugs and temperature sensor into the #3 cylinder head. Finally, we fastened the large oil return line that runs underneath the motor from the engine case to the oil tank. Becker also fitted the throttle linkage plate and ancillary components while I mounted the speed and reference sensors next to the flywheel ring gear and checked the clearance to ensure the DME unit would receive an accurate signal.

The induction system was then ready to be mounted on top of the motor. Becker placed the freshly Extrude-Honed intake plenums atop the intake ports, while I took a few moments to reseal the fuel injectors. After inserting the injectors onto the plenums, we proceeded to set the black anodized fuel rails into position. New braided stainless-steel fuel return lines were made to replace the old, cracking and expensive rubber lines that run from the fuel rails to the fuel pressure regulator and diaphragm damper. Attachment of the injector harness connectors completed the fuel system portion of the motor.

Next on the agenda was fitment of the exhaust system. The cylinder head exhaust studs were liberally coated with anti-seize compound in the event that the exhaust system would need to be removed in the future, making disassembly fast and relatively painless. Removing frozen or snapped exhaust studs is a 911 owner's nightmare. Becker and I installed the exhaust headers upstream from Dansk's stainless-steel sport muffler. The headers were originally designed for straight-through megaphones, used without mufflers. Special 2-inch adapters were fitted to the headers, since this street engine needed a muffler to civilize the 911's signature raspy, screaming cacophony.By this time, the custom spark plug wire set from Magnecor arrived. The remaining outer engine tin was fastened and holes drilled to allow the second set of plug wires access from the top to the bottom of the engine. Rubber grommets were inserted to protect the lower plug wires from being sliced by the sheet metal. RSR-spec hold-down clips ensure that the lower plug connectors are firmly held in place and provide "race" aesthetics for boulevard cruising and bench racing alike.

To further maximize the potential of this motor in street guise, Becker increased the throttle body bore an additional 3mm before mounting it to the intake plenum, along with the full throttle switch and idle air stabilizer. The airflow meter and airbox were then installed as a unit. Finally, the remaining mounting brackets for sensors and switches were placed in their respective locations. After three months and approximately 37 hours of labor, the 3.5L twin-plug monster is finally ready for installation!

Prep work and reinstallation

Vision Motorsports shop foreman Mike Olsen was recruited to handle the delicate balancing act of installing the motor and transaxle into the freshly detailed Carrera engine compartment. He expertly mounted and wired in the ANDIAL signal splitter next to the DME computer located under the driver's seat, then ran the wires back to connect to the twin Bosch coils, which were neatly secured in Steve Becker's jewel-like mounting bracket. The DME computer was also opened up and the socketed 28-pin EPROM swapped from 911Chip's 3.2L single-plug ignition program to their custom program for the now larger displacement, twin-plug motor where additional fuel and less ignition advance would be required.

Olsen installed the 240mm clutch assembly onto the flywheel, tossing aside the standard rubber-center disc in favor of a new 3.0L 930 spring-centered unit. The G50 transaxle was attached to the motor, and the starter motor bolted into position. The Dansk muffler was also temporarily removed in order to gain some extra clearance when fitting the motor into the engine compartment and to avoid potentially damaging the huge 84mm exhaust tips on each end during this process.