As part of the conversion, standard GT3s get an RS flywheel, which cuts 15 pounds from rotating masses. All cars get a GT3 Cup clutch and pressure plate as well as one of two exhaust setups. The first is SharkWerks’ popular muffler bypass (250 sold and counting — for 911s that are by no means common). No power advantage is claimed, but the bypass lets more sound through while removing 16 pounds. The green RS’s titanium tips save a further two pounds, but Ross says he won’t produce them because Porsche just introduced an identical product.
Those after more noise and even less weight can pick the “race” exhaust, which Ross says is too loud for street use but deletes 57 pounds while adding a little top-end power (8–10 hp). The latter features two lightweight stainless-steel mufflers and weighs 11 pounds. “It comes with ear plugs and requires proof of helmet,” chuckles Ross. The 3.9 still utilizes the factory headers and catalytic converters, which Ross feels are well designed. The same goes for the factory airbox, which means the 3.9 looks identical to the 3.6 when you pop the engine lid.
The final and most complicated piece of the puzzle was the engine management. Evolution Motorsports has brought ECU tuning in-house and uses an emulator that allows live tuning in three-dimensional maps for fuel, ignition, cam timing, throttle, and more. When the tuning on its Mustang chassis dyno was complete, Ross says the 3.9 moved from 385 rear-wheel-hp to 458 rwhp, which he estimates is 502 hp at the crank. Torque moved from 274 to 326 lb-ft, for an estimated 355 lb-ft of torque at the crank. For the record, Porsche claims 415 hp and 300 lb-ft, figures that are probably conservative.
The best numbers were generated on 93-octane pump gas, but a separate map for 91-octane gas made only a little less power while a map for the “race” exhaust made a little more. Critically, the 3.9’s gains don’t come at the peaks alone. Its power and torque curves mimic the stock ones but add 70+ rwhp at high rpm and 50+ lb-ft throughout the lower range.
“There’s a big jump in horsepower and torque down low compared to the already good 3.6,” opines Ross. “Where the factory camshafts and tuning begin to fall off, this motor continues to make power to 8800 rpm — where it’s just five horses down from its peak.”
Those ponies don’t come cheap. The 3.9 conversion runs $25,000 on a GT3 RS and $26,000 on a standard GT3 (to cover the RS lightweight flywheel). The build takes four weeks, with the shop handling initial break-in. Ross says that the job can stretch to six weeks and cost more if additional work is required. The first customer car, for instance, had 35,000 miles and wanted (but did not need) new rod bearings and connecting-rod bolts.
This RS’s chassis is largely stock. It’s running the same aggressive alignment we liked the last time we drove it, but a TechArt hydraulic front-end lift system has been added. It raises the front end by about two inches at the touch of a button and lowers it automatically at 37 mph. The kit adds stiffer front and rear springs and costs $5,999 against Porsche’s Front Axle Lifting System, a $3,490 option on the 2010 GT3. We’ve heard owners note that dozens of spoiler lips cost less — a financially sound philosophy but one that requires a stomach for scarred spoilers. For our part, we found TechArt’s system quick, quiet, and helpful. It reduced the hassle factor around town, while the stock, electronically-variable PASM dampers took the stiffer springs in stride.
The only other chassis change is a set of forged-magnesium one-piece wheels wearing Pirelli PZero Corsa Systems. The Champion Motorsport Monolite MS 171’s “split-five-spoke” design is similar to the stock GT3’s wheel, but the MS 171s weigh 18 pounds front and 19 pounds rear, for a savings of six and seven pounds per rim, respectively. Altogether, they shave 26 pounds of unsprung, rotating mass.
If it looks like this RS is missing something, it is. Its trademark black side stripes have been swapped for ghosted green stripes that no longer interrupt the flow of its lines. Inside, a Brey Krause harness bar locates Schroth harnesses that thread through European one-piece GT3 shell bucket seats. Along with the lighter wheels and exhaust, the seats help save more than 100 pounds.