 The 240mm Sachs clutch assembly...  The 240mm Sachs clutch assembly for the G50 transaxle, mounted and ready for duty. |
 Vision tech Mike Olsen carefully...  Vision tech Mike Olsen carefully attaches the G50 transaxle to the 3.5L motor. |
 Underside view of the engine...  Underside view of the engine shows off George Narbel's ceramic coated 1 5/8-inch headers and stainless-steel Dansk sport muffler. |
 3.5L motor installed in car...  3.5L motor installed in car prior to initial start-up. |
 Steve Wong from 911Chips makes...  Steve Wong from 911Chips makes changes to the fuel and timing maps via his laptop to optimize the air/fuel ratio across the entire rpm range for silky smooth drivability and maximum horsepower. |
 Steve Wong and dyno operator...  Steve Wong and dyno operator Nick Emens from Vision Motorsports collaborated to extract 246 whp from the 3.5L motor on the Dynojet 248C. |
 Nick Emens throttles the 3.5L...  Nick Emens throttles the 3.5L motor to its third gear 6840 rpm cut-off on Vision's Dynojet 248C. |
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.
Engine break-in
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