Turbo Cab

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This might be the end of the story for most. But, you know, boy meets car, boy and car live happily ever after — it was really only the beginning of a new chapter for Mervin and his 993 Cabriolet.

“I suffer from Upgrade-itis,” he admits. “If some is good, more is better. And more is never enough.” Compound­ing his hard-to-treat affliction, Mervin became aware of the aforementioned rare factory special shortly after he bought the 993. He also liked the 993 Turbo coupe, so he decided to create the best of both worlds.

“I certainly would have been money ahead had I sold the Cab and bought a factory Turbo hardtop,” he says. “But what fun would that be?”

From the outset, Mervin decided to split the project up into digestible chunks rather than tackle the transformation in one, big process. The engine and driveline were first to receive attention. “My goal was to have the car drive­able in between upgrades,” he says. “I look forward to driving this car.”

Researching shops that could handle the work led him to TurboKraft in Mesa, Arizona. A phone call to shop owner Chris Carroll led to the conclusion that transplanting a real 993 Turbo engine was a better move than turbocharging the existing, naturally-aspirated 3.6. Not long after, a 993 Turbo engine, complete with wiring harness and engine control unit, were sourced from LA Dismantler in SoCal.

Carroll opened the motor and found that the internals were still in fine enough shape to use without a rebuild, so the pistons were simply de-carboned before the case was buttoned up. The cylinder heads, on the other hand, were rebuilt with new guides and oversize exhaust valves. In the quest for more power, the stock K16 turbo­­chargers that Porsche originally specified were remanufactured and fitted with the larger compressor wheels from K24 units.

The factory Turbo mufflers were then modified for improved airflow as well as a louder exhaust note. These terminate in stainless-steel Dansk Sport exhaust tips. When the engine was purchased, it came with a modified ECU, which helped the refreshed engine produce a claimed 385 hp and 426 lb-ft of torque at the wheels.

“This is approximately 450 horsepower and 500 pound-feet at the flywheel — stronger than a 993 Turbo and comparable to a street 993 GT2,” says Carroll.

This 993 retains its original six-speed transmission rather than the G64/51 unit used in the 993 Turbo. “Since Turbo gearboxes are rare and expensive, with longer gearing more suitable for the autobahn than street driving, the decision to retain the shorter C4 transmission was a clear one,” explains Carroll. “It results in a car that’s more fun to drive on the hilly, narrow roads of Northern California.

There’s one hitch, though: “The Turbo six-speed is nearly an inch longer than the non-Turbo transmission,” notes Carroll. “This positions the engine farther back in the chassis, and all of the engine peripherals (such as) the air-guide sheetmetal, motor mount, intake plenum and tubes, intercooler and air guide, (and) exhaust tips are designed to fit in this aft position.” Carroll says you can run into interference and serious serviceability problems if the 993 Turbo engine is merely installed in the same spot as a naturally-aspirated 3.6.

To position the twin-turbocharged flat six in the same place it would be in a 993 Turbo, an engine-and-clutch spacer was engineered and fabricated. Carroll also installed what he calls an “RS Touring flywheel,” which is a bit heavier than a 993 RS flywheel to keep the engine from stalling at idle but far lighter than the C4’s original dual-mass flywheel. A 993 Turbo clutch assembly was used with the accompanying hydraulics, including the power-steering pump, reservoir, lines, and slave cylinder.

With more power came more motivation to improve the rest of the car’s performance, particularly in regards to the braking and handling. To that end, a set of Bilstein PSS-9 coil-­overs and a front strut brace were added. Adjustable rear toe-links were installed to ensure that the car could be correctly aligned when lowered. Once the car was delivered back to Mer­vin’s home in the Berkeley hills, it was handed over to S-Car-Go in nearby San Rafael, where factory 993 Turbo brakes were installed to allow the Porsche to stop as well as it accelerated.

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