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.
The motor/transaxle assembly was now ready to be jacked up into the car, and having access to a lift made the install seem virtually effortless. Literally taking just a few minutes, Olsen had the motor and transaxle secured using new ClubSport engine and transmission mounts. These mounts are considered stiffer than stock rubber mounts, but not nearly as harsh as full-race-spec hard mounts. They were originally installed on the rare 3.2L ClubSport from 1988, but are readily available today. These mounts have evolved into a common upgrade for more pedestrian 911s. The constant-velocity joints were then reattached to the transaxle, the clutch slave cylinder installed and the bolt for the shift coupler tightened. The oil return line and oil suction hose were also connected. The Dansk muffler was then properly repositioned while the oxygen sensor, along with the oil breather and vacuum hoses, was connected up top. A K&N air filter replaced the stock paper element and nestled in the modified airbox (a la Carrera Cup cars). The engine wiring harness connectors were attached to the airflow sensor, idle speed stabilizer and throttle switches. Finally, the braided stainless-steel fuel lines were connected to the fuel filter and the cruise control cable attached.
Little by little, the brawny 3.5L was getting close to initial fire-up, and all that was left to do was install the rear sway bar, mount the air conditioning compressor and properly tension the belt. At the time, I wanted to have a/c as a viable option in the summer heat of Southern California, but quickly decided to eschew such creature comforts and have subsequently removed all a/c components in order to shed weight and tidy up the engine bay. While Olsen reconnected the battery and hooked up a battery charger to assist with the cranking amps, I filled the oil tank up with 10 quarts of oil. It is common sense but still important to note that the motor should not be started until oil pressure has built up. Olsen removed the DME relay located next to the DME control unit to ensure the motor would not start and proceeded to crank the starter for 20-30 seconds to build oil pressure as well as check for potential oil and fuel leaks. Having quickly gained oil pressure and not finding leaks of any kind, the DME relay was reinserted and the motor deemed ready to start.
There are few things in life more gratifying for a gearhead than listening to the motor upon which he or she spent countless dollars on and hours sweating over being brought to life for the very first time. The big flat-six announced its arrival with a definitive roar, the slight lope at idle from the cam overlap and deep bass from the exhaust reverberating through Vision's sterile facility. Olsen wasted no time in quickly increasing the idle to 2000 rpm for a 10 minute period, then to 3000 rpm, then to 4000 and finally to 5000 rpm before shutting the motor down and draining the oil. Varying the rpm helps allow the rings to seat as well as create proper wear patterns for the new components. Higher rpm also mean higher oil pressures, ensuring none of the new components would potentially starve for lubrication during this critical period.
Many engine builders share the philosophy that the proper break-in for a new motor is driving the car like an idiot (within reason of course), meaning hard on the throttle to various rpm (in this case 5000 rpm max for the first 1,000 miles) and then letting the motor decelerate on its own in gear, which creates vacuum and helps properly seal the piston rings. I eagerly drove the car like I stole it, reaping the benefit of increased power with a big grin on my face while at the same time putting miles on the motor as quickly as possible in anticipation of heading back to the dyno after 1,000 break-in miles had accrued. Whereas the stock 3.2-liter seemed to do next to nothing down below 4000 rpm, the 3.5L starts pulling like a freight train from as little as 2500 rpm. No peakiness or flat spots here, just a nice, progressive powerband that doesn't stop until the rpm cut-off at 6840 rpm. The 3.5L hurtles the 911 through every gear with authority and, without caution, distracts you from realizing how fast you are going until you until you glance down at the speedo and see triple digits. While the performance of the 3.2-liter engine in 1988 was world-class (although many grocery getters today have more power), the big 3.5-liter motor today in a relatively lightweight chassis is simply awe-inspiring by any standard. There are no words adequate to describe the push in the back at full throttle, with the engine behind you howling for more. The extra displacement in conjunction with carefully selected go-fast bits is, indeed, aircooled nirvana.
Dyno testing As good as this motor feels on the butt dyno, the Dynojet 248C would tell the tale. Using the baseline 3.2L figures of 199 whp and 182 max lb-ft of torque, I couldn't wait to get the car strapped down on Vision's dyno to measure the actual improvement. Steve Wong from 911Chips was kind enough to offer his services with tuning the motor and met me at Vision's facility with his trusty laptop, emulator and Innovate LM-1 in hand. Right out of the box the big 3.5L made 239 whp and 215 max torque, eclipsing my original target goal without Wong even beginning to work his magic. He logged and analyzed the air-fuel ratios after each run and precisely altered the fuel and timing maps for maximum horsepower and torque while still comfortably using the pathetic 91 octane pump gas that curses all Californians. Twelve dyno runs were made in all, with the motor responding to Wong's tuning tweaks after each run. Finally, a maximum (and repeatable) peak of 246 whp at 6200 rpm and 224 lb-ft of torque at 4800 rpm was extracted. Those lofty numbers translate to more than 80 hp per liter and put this engine in the same stratosphere as the revered early 911S mechanical fuel injected, and the later 993 3.6L VarioRam motors, pretty heady company indeed.
So how much does a hot-rod 911 SC or Carrera street motor cost? The answer is not for the faint of heart. While the $10,000-$25,000 purchase price of many '78-'89 SCs and Carreras on the open market makes them affordable for just about any car enthusiast, original and aftermarket Porsche parts prices haven't seen the same erosion as time passes. A professionally built, normally-aspirated motor like the 3.5L twin-plug detailed here can cost as much as the value of the car itself, depending on the selection of parts and the attention to internal detail a skilled 911 engine builder provides. Non-Porsche enthusiasts may scoff at the horsepower-per-dollar ratio, but consider that many models from this vintage in the hands of enthusiasts can also weigh well under 2,600 pounds. That impressive power-to-weight ratio combined with already excellent brakes and legendary handling makes the classic 1980s era 911s that has benefited from this type of heart transplant a difficult car to best on the street or track. For discerning 911 owners, there really is no substitute.
Special thanks to Steve Becker, Dwain Dement, Steve Wong, Steve Weiner and Dave Cardone for their insight, guidance and patience during the course of this engine project, along with the fanatical members on Pelican Part's BBS for their support and encouragement. For a complete list of machine work and replacement part numbers, visit www. europeancarweb.com
For an excel table containing a complete list of parts numbers and machine work performed on Project 911's 3.5-liter engine, click here