NOT-SO-GENERAL MOTOR
Mid-engined and low slung, a 987 Cayman is already exotic. Add eight cylinders of Detroit muscle, however, and it becomes an altogether different kind of Porsche…
A 6.2-litre LS3 V8-powered 987 Cayman.
Chevrolet Ls-series engine conversions are a hot topic in North American car culture. It doesn’t matter what model you care to think of, someone, somewhere is trying to mount an LS beneath its bonnet. These pushrod V8s enjoy popularity for their affordability, ubiquity and substantial aftermarket development options, affording owners big bhp and a tonne of torque for surprisingly little spend, even when sourcing a brand new crate engine. The first two factors are typical of the United States and Canada, where the General Motors LS family has powered two decades of production cars that aren’t commonly available in Great Britain, but the other benefit survives a transatlantic crossing. Everyone from General Motors itself to specialised drag racing workshops sell fully dressed LS variants that range from mild to fourfigure horsepower levels of wild. All this got 987 Cayman S owner, James Hewett, thinking: could an LS engine be mounted in place of his car’s flat-six? Porsche purists, look away now.
It was no idle question. James had always planned to upgrade his midengined marvel, though the decision was made for him when his Cayman’s beating heart dropped a valve seat in the middle of a busy car park. Three routes forward came under consideration, each offering substantially more power. First, James could invest in a rebuild at independent Porsche specialist, Hartech, taking the opportunity to invest in one of the company’s celebrated 3.9-litre flat-six conversions, adding bulletproof reliability and increasing performance throughout the rev range. His second train of thought travelled along the same track as the first, but added a turbocharger to the mix, while his third and, as it happened, preferred choice was to ditch the 3.4litre Porsche engine and buy a V8. No British or European 987 owner had ever installed an LS V8 in their car before. And that’s exactly why James chose the all-American option.
SWAP SHOP
Birmingham-based V8 conversion specialist, Dynotorque, was charged with carrying out the transplant. Head honcho, Craig Taylor, is the foremost expert in the UK for adding Chevrolet power to everything that moves, having previously fitted bent-eights to cars as varied as an Aston Martin V8 Vantage, several BMW M3s and a Delorean DMC12. Most importantly (and impressively), however, he’s mounted an LS V8 into
the rear of three water-cooled 911s to date. Understandably, this filled James with confidence, leading him to call on all of Dynotorque’s experience in a build spanning four months.
Craig started by selecting the right engine for the application. James wanted his Cayman to produce more than 500bhp, whilst still remaining quiet and tractable enough to use regularly on the public road. His request pointed the pair to the Ls3-generation LS V8. Introduced as Corvette’s new base engine for the 2008 model year, the 6,162cc unit produces around 430bhp and 428lbft in standard trim, offering plenty of potential for more, including the benefits of supercharging. To find the extra power James wanted, he also invested in an official LS3 Power Upgrade kit, offered by Chevrolet Performance. Engineered by an in-house enthusiast division at General Motors, this upgrade package is designed to provide a modest power increase without requiring LS3 owners to modify their engine block, air intake or exhaust system. Fitted to an otherwise standard engine, the system raises peak power by forty ponies to a claimed 470bhp and 440lb-ft torque.
Chevrolet Performance achieves the power increases by replacing the cylinder heads and camshaft. Revised intake and exhaust porting improves airflow through the heads, while 276cc intake runners have 19cc more capacity than the standard LS3 items and improve power output at higher revs. The Power Upgrade camshaft is identical to the one used in the seven-litre LS7, a higher-performance, ultra-lightweight V8 used in the C6-generation Corvette Z06 and noted for being the largest displacement small-block engine ever manufactured at its time of production. With the LS7 cam providing longer duration and higher lift than the original LS3 part, it also increases airflow to aid performance.
Of course, all of this counts for nothing if the motor won’t fit into a Cayman engine bay. It’s here that Craig really earned his money. Small-block construction makes the LS3 far more compact than most Detroit iron — and all-alloy construction means the 183kg Chevrolet unit weighs little more than a Porsche flat-six — but Dynotorque still had to budget under-bonnet space carefully. “The LS3 sits back-to-front compared to the Porsche engine, so there’s really not much space for the ancillaries,” Craig says. “We fitted an electric water pump and the front pulley from a front-wheel drive LS application, purely to save space.”
The engine is longer than the Porsche flat-six, leading Craig to remove the original bulkhead and fabricate a replacement that sits three inches further forwards and protects the cabin from excessive heat and sound levels. Some 987 LS engine conversions in the USA run without replacement metalwork here, but James and Craig wanted to keep this Cayman road usable. By placing the engine in the same location as the flat-six, Dynotorque has also been able to keep the gearbox close to its original position and retain the factory driveshaft angles to encourage durability.
Once the layout was finalised, the LS3 could be fitted to the Cayman with a series of custom engine mounts. These run down the sides of the engine bay and have been deliberately overbuilt for safety. “They might be a little bit heavier than a perfect mount, but the new engine makes a lot of power and torque,” Craig continues. “This way, we know they’re strong.” A custom Car Interiors engine cover perches over the top, providing another layer of soundproofing and adding subtlety.
Look under the car and you’ll see it’s false modesty: Craig has used his metalworking skills to craft a unique 2.5inch exhaust system following the same route Porsche mapped out. “The exhaust runs out through the chassis legs, kinks past the suspension and joins up at the back. The old system was two inches in diameter. Believe me when I say it’s a lot of work to get anything bigger through that space!” Starting with a set of LS7 exhaust manifolds, the exhaust flows through twin oval boxes and two round boxes to strike a balance between civility and power. Matched with a reutilised Porsche airbox containing a high-flow K&N filter, the pipework raises peak outputs to 512bhp and 454lb-ft.
MATCHED WITH A REUTILISED PORSCHE AIRBOX CONTAINING A HIGH-FLOW K&N FILTER, THE PIPEWORK RAISES PEAK OUTPUTS TO 512BHP AND 454LB-FT
COG IN THE MACHINE
Despite the monstrous torque increase provided by the V8 (lubricated with Millers Nanodrive oil), this Cayman uses its original Getrag 466 transmission, allowing James to keep access to six forward gears. The gearbox has been fitted with a Kennedy Engineered Products adapter plate and shifted back ten millimetres to accommodate the GM engine, but its internals remain unchanged. A Kennedy Engineered Products Stage 1.5 clutch and flywheel package has also been fitted, ensuring
this powerful Porsche can stand up to high-performance antics. In the near future, James will be upgrading to the same company’s Stage 2 kit for complete peace of mind.
The gearbox is further transformed by a Numeric Racing 987 transmission bundle, including a short-throw gear shifter and revised shifter cables. It’s one of James’ favourite modifications. “It completely transforms the character of the car,” he says. “The shift feels very precise now: there’s no excess and you can very quickly find where you need to be. I know it’s a worn-out analogy, but it really does feel like a rifle bolt.” Designed to fit in place without any further modifications, the Numeric system reduces lever movement by approximately forty percent and uses ball bearings on all axes.
Precision and responsiveness also define the limited-slip differential that translates drive to both rear wheels. Rejecting the standard Porsche open diff as inappropriate for such a highpower application, James and Craig have fitted a Wavetrac 40.309.175WK helical item. Due to its unique construction, the Wavetrac unit offers the Cayman more flexibility than other limited-slip designs. Under most normal conditions this differential operates like a torque biasing unit — offering predictability in poor weather and tight corners — but the integral Wavetrac device ensures the diff maintains drive whenever a wheel spins and creates zero axle load. It gives
James the predictability needed to power his car with absolute confidence.
And James does love to spin the rear wheels. “I’m a real fan of oversteer,” he grins. “It’s part of the reason I wanted to build the car in the first place. Now, my Cayman wants me to go fast, but it also wants me to go sideways!” The new engine makes the car twitchy under power and it’ll spin up the sticky Continental tyres in third when it’s dry, or fourth if it’s raining. “I have to make sure the side windows are clean — I spend so long looking out of them!” he laughs. The surfeit of grunt over grip can demand more mindful inputs too, James having to apply power carefully and progressively when driving neatly. “Something as simple as a third-gear
overtake can turn into tyre-smoking oversteer if I’m not careful,” he tells us.
His Ls-engined Cayman loves to play the hooligan, but it hasn’t forgotten how to be a Porsche. Standard components retain the connected, feelsome steering and responsive brakes that win plaudits in ordinary 987s, while the untouched suspension retains the pliancy needed for day-to-day road use. James plans to fit Bilstein B16 front coilovers to drop the car by 20mm and Craig advises that V8-converted 911s generally need rear lowering springs to return to their original ride height. Far from adding mass, the all-alloy V8 maintains (and can reduce) kerb weight, allowing the Porsche to retain its original road manners when its master isn’t hell-bent on punishing it.
New electronics complete the conversion. Using the same techniques he established when equipping a 997
Carrera 4 with an LS3, Craig gathered the Can-bus protocols from the original engine control unit, copied all of the data and uploaded it to an Emerald K6 ECU. The process allows the Emerald to operate as a standalone system and output all the correct signals to the remaining Cayman electronics, ensuring the dashboard and dials, warning lights and safety systems all function entirely as Porsche originally intended.
The control unit has also been used to calibrate this Cayman’s V8 engine on Emerald’s own rolling road at the company’s base in Norfolk, a process made easier by the LS3’S relatively benign state of tune. Three different maps have been built into the system and are activated by a cabin-mounted switch, allowing James to change the car’s character at will: a standard setting for general road use provides a clean and smooth 512bhp, ‘valet mode’ limits throttle inputs and caps peak revs at 2,000rpm, while an overfuelling map provides exhaust pops and bangs for when James wants to draw a crowd. The final mode automatically defeats the traction control too, for full shock and awe effect.
Regardless of the map he’s making use of, James and his 987 turn heads wherever they go. “I was arriving at a car show at in Sandbanks, a small peninsula crossing the mouth of Poole Harbour on the English Channel, soon after I got the Porsche back from Craig at Dynotorque. Everyone was looking around as they tried to work out what the hell was going on,” he says. “They could hear a muscle car pulling into view, but all they could see was a dinky little Porsche Cayman!” This side of the Atlantic, there really is nothing else like it.
l