Following an extensive test drive and visit to Shark Werks' HQ in Fremont, California, automotive industry and Porsche veteran Ian Kuah shares his thoughts on 9tro Online Magazine:
Shark Werks GT3 RS 4.1 - Big Bang Theory
A GT3 RS with turbo punch, but no turbos. Pure cubic inches rule the roost here.
One of the most basic rules in motorsport is that you should only ever change one thing at a time. This way you can nail down cause and effect, while avoiding confusion over which tweak has made what difference. Following the same rule when tuning a road car is also a smart thing to do.
This was going through my mind as I drove to a familiar test road in the same blue and orange Shark Werks 997 GT3 RS 3.8 that I piloted almost two years ago when the car was fresh out of its wrapper.
The Diablo Mountains, east of San Jose, offer some of the best and most spectacular driving roads in Northern California. Bordering the local state park, Route 130 starts in the foothills by Highway 680, and winds its way up Mt. Hamilton towards Observatory Peak at 1,284m (4,213ft) above sea level, and down the other side.
Running across Mt. Hamilton for 22.5 miles, Route 130 has considerably more gradient than flat, a short few straights, many open, but even more numerous tight bends, with the occasional hairpin thrown in for good measure.
In all, there are 365 curves here, one for each day of the year, and all the tighter corners are cambered the right way. The backdrop to this sinuous piece of tarmac is a rock face on one side and a sheer drop on the other. This is a drivers’ road par excellence!
The last time I came here, the RS 3.8 had already acquired Shark Werks’ full suspension kit, but its motor was stock apart from their lightweight titanium/stainless steel hybrid sports exhaust and EVOMS ECU upgrade. A healthy 470bhp at the flywheel was the order of the day.
So what has changed? Outwardly almost nothing, apart from that big Baron RS rear wing that sits three inches higher up and offers eight degrees more angle of attack. A side benefit is better visibility in the rear view mirror!
The big news is that Shark Werks has leapfrogged their famous 3.9-litre conversion and morphed this GT3 RS 3.8 into a 4.1. Appropriate badges on the engine’s air box, doorsill entry plates, and the carpet behind the lightweight race seats constantly remind you of the fact.
On the face of it, Shark Werks 3.9 conversion was already a weapons grade conversion. To my surprise, it had more torque than the factory RS 4.0, so when Shark Werks’ boss, Alex Ross e-mailed me to say that the 4.1 litre upgrade was finally ready for testing, I could not wait to get behind the wheel.
From the word go, the 4.1 feels quite different from anything in the Porsche GT3 road car world that has gone before. Where the stock 3.8 with its single-mass flywheel revs quickly and smoothly to its redline, and the 4.0 is more of the same but with a bigger punch, the Shark Werks 4.1 feels like a 4.0 on steroids, coupled with some aspects of the new 991 GT3’s even higher-revving motor.
Revving fast and hard is not the only characteristic worthy of note here. While the 3.8 and 4.0 factory motors produce more and more power as they head for their respective red lines, the 4.1 feels like it is bursting with energy trying to force its way out of the motor as well. There is a fundamental difference in the way this motor answers the throttle, which makes this big engine all the more enticing.
The irony is that with 540bhp at 7,950rpm and 400 ft lb (542 Nm) of torque on normal 93 Octane pump gas, the naturally-aspirated flat-six is now so powerful and so responsive, I quickly realised that I could not use anything close to its full potential on this test road.
The RS 4.1 is so much quicker in a given situation that it literally compresses the straights between the bends on this familiar road. Where I previously would have revved the motor out in third and then snatched fourth between a couple of the corners I know, now I am still in third and have to start braking in the face of the absurdly higher speeds attained in what seems like the blink of an eye.
If you crunch the numbers, the reason instantly becomes clear. Output has jumped 90bhp over the stock 450bhp 3.8-litre motor, with torque up an amazing 112Nm. In parenthesis, that also means 40bhp and 82Nm over the 4.0, and 38bhp and 61Nm over Shark Werks own 3.9.
In fact, the 540bhp and 542Nm of torque now on tap compares very favourably to the 997 Turbo 2’s outputs of 500bhp and 650Nm of torque. This is especially so in terms of power-to-weight ratio, since the stock GT3 RS 3.8 starts life some 200kg lighter out of the box than the Turbo.
With its chassis already uprated in all respects by Shark Werks, the 4.1 motor does not overpower the handling and grip in fast road driving so long as you are sensible with the throttle.
If you have an open corner with good visibility, it is not difficult to punch the big, stocky rear Michelins off their perch and indulge in some tail out gymnastics.
With this much grunt on tap, I can imagine doing some long and lurid power slides on a racetrack. But that is not the raison d’etre of this amazing car. This is a GT3 RS that goes as hard as a Turbo but with throttle response that the forced aspirated car can only dream of.
Its big displacement motor simply makes everything more effortless, and will pull away from 1,200rpm in fourth at town speeds. If you could slip the clutch and pull away in fourth gear, you could drive everywhere in that one gear within all normal road speed limits. You only have to look at the torque curve to see why. The 4.1 makes between 88 and 108 Nm more than the 3.8 between 2,900 and 5,300rpm, and this is substantially more than the factory 4.0 whose peak is only around 30 Nm more than the 3.8.
To get into the real nitty-gritty of the 4.1-litre motor, I spoke to John Bray, the man responsible for engine development and special operations at Evolution Motorsport (EVOMS), who developed this big bang motor alongside Shark Werks own resident boffin, James Hendry.
“The 4.1 is not a totally new concept, but rather the culmination of work that began six years ago,” John explained. “While it may have appeared that the 3.9 was the culmination of our development programme three years ago, in reality it was just a waypoint on our journey towards the 4.1.”
“A lot of parts from the 3.9 are carried over,” he continued. “We use a similar piston and dome shape with pistons altered to take into account the different pin height required for the longer stroke.”
With the bore staying at 104.5mm, the stroke goes from the familiar 76.4mm to 80.44mm. This requires an all-new crankshaft, so the opportunity was taken to make this something special.
“The new crank is bespoke to our specifications, machined from a solid billet of 4340 high alloy content steel with 12 radically profiled counterweights that are lightened and dynamically balanced, John explained. “It has an Omicron surface hardening finish to 2.0 microns and also features a Multi-Rate rod journal oiling system.”
“This material is strong but not brittle and is the best choice for a street application,” John explained. “In direct comparison, the basic crank without its gear weighs about 0.25 kg (0.56 lb) less than the stock item, but is even stronger in tensile strength terms and is good for 9,500rpm.”
“We also took the opportunity to build in some efficiency improving features like knife edging the counterweights to reduce hydraulic drag in the oil,” he added. As any form of internal drag reduction releases more power for free, EVOMS put a lot of time into addressing the oil flow in the motor to reduce windage in the crankcase.
The main bearings are Porsche OE components, but the connecting-rod bearings are bespoke. They are a little smaller than stock and made from a harder material to handle the higher loadings.
They are also coated with a special dry lubricant that is supposed to last the life of the engine. This is mean to act as an oil cushion in case of a drastic and sudden loss of oil pressure in the motor.
“Porsche did a very good job of the oil spray system in the Metzger motor,” said John. “We made a few small modifications to this that are not necessary all the time, but are simply there to cope with a just in case situation.”
“Most of today’s well known brand fully synthetic oils like the Mobil One that Porsche and we both use are really good,” John explained. “I have seen cars sit around for six months and then start up with no damage to the internal metal surfaces upon later examination.”
The Teflon-coated pistons come from a European manufacturer who makes low volume pistons for race and high performance road application. The skirts of the new pistons are almost the same length as the stock ones, but the domes are to EVOMS spec.
The wrist pins are titanium and the three oil control rings are also specific for these pistons. Despite being larger, each piston/wrist pin combination saves 20 grams over the stock 3.8 ones. “The 4.1 R motors we build for the Cup Car and RSR use full race pistons from the same company,” said John.
With a bore size of 104.5mm, EVOMS were right on the edge of what is possible with this crankcase. “This is literally the thinnest wall I was prepared to use to avoid distortion,” said John.
“Initially, we considered using new barrels, but the cost was too high in relation to any possible benefits, so the new pistons sit in special upgraded iron liners in the crankcase,” he explained.
Unsurprisingly, the connecting rods are from Carrillo, who make a very strong steel alloy rod in their famous H-section design that is almost as light as the OE titanium rod.
I have heard this from several other sources, and John reiterated the fact once again. “As they stretch over time and use, titanium rods are maintenance parts,” he said. “That does not matter in a race engine, which is being rebuilt all the time, but in a street motor, this is the last thing a client needs.”
Thus EVOMS were very happy to use the steel alloy Carrillo rods, which are cheaper, just as light, 20-percent stronger, and will last the life of the motor. In addition, Carrillo uses its own high quality fastening bolt design that actually strengthens the rod.
“In terms of compression ratio, we settled on 13.0:1 (including the head gasket) where the stock 3.8-litre uses 12.2: 1 and the 4.0-litre is 12.6: 1,” said John. “This was absolutely the maximum we could use as, like the factory engineers, we encountered some detonation over 13.0:1 with pump gas. Incidentally, the race motors have a 13.5:1 compression ratio, but they run on 109 Octane race fuel.”
Shuffle pinning the two halves of the crankcase was a very common practise when rebuilding the old 2.7 litre motor with its relatively weak casing. EVOMS carry this out as part of the build process on their 3.9 and 4.1 litre motors due to the huge amount of torque these motors make.
Leaving no stone unturned to ensure strength and longevity, they also use A1 Technologies H11 Head Studs, which have a tensile strength of 260,000 psi. These unique studs have a feature known as a ‘dog point’ that seats the stud in the block and pre-loads the fastener for an accurate and repeatable torque sequence during fitting.
“We learned a lot from development of our high-powered Turbo motors,” John continued. “Some of these make over 1,200 Nm (900 ft lb) of torque, so a strong bottom end and stable crankcase is a linchpin of the motor.”
While enthusiasts refer to all the 911 Turbo and GT derived motors as being the Metzger or GT1 block, Porsche did evolve the basic design a lot even between the 996 and 997 eras.
“We noticed the differences in the course of our development of these engines,” said John. “Porsche changed the quality of the alloy from 996 to 997, so the newer motors benefit from both better materials and castings. Thus, we prefer to base our 3.9 and 4.1-litre conversion on the later motor.”
The 4.1-litre motor also benefits from a bespoke higher flow oil pump for greater flow and overall volume of oil. This is made from a billet as opposed to the cast OE item. The OE under-piston oil spray system is unchanged.
The greater torque inherent in a larger displacement motor, particularly a long stroke one, allows you to use a wilder camshaft profile for more top-end power. Modern fully mapped ignition, fuel-injection and variable valve-timing also smoothen out the effects of the higher lift and greater overlap and keep things civilised for street use.
“In this case it is a matter of balancing out the total package of intake, exhaust, displacement and the expected driveability characteristics against emissions.”
As this is a street rather than race motor, the stock cylinder heads, valves and valve springs are used with Shark Werks; gas-flow job and race-style valve guides for longevity. “The OE design of all these parts is very good and well able to handle the extra displacement,” said John. “The cam followers are good to 8,800rpm, which is more than what we need and the hydraulic lifters keep things maintenance free.”
“Another reason for leaving the heads and valves alone is that we are almost out of room in the combustion chambers,” John explained. “But in reality we did not need to do any additional work here as we had already met our power and torque targets.”
“While we probably could get a few more horsepower out of the heads, the law of diminishing returns kicks in, and each extra horsepower would be a very expensive one.”
I was curious that the 4.1 uses the stock 3.8 air box and plenum, since Porsche went to great lengths to improve this area on their RS 4.0.Just as we went to print, Alex told me that they have now signed off a new airbox that flows 62-percent better than the stock 3.8 airbox, for an additional 10bhp on top.
Another area that EVOMS is still working on is the exhaust. Using the Shark Werks upgrade exhaust has produced very good results, but John thinks that this system with its 200-cell free-flow metal catalysts can be further improved for the big engine.
In the final analysis, what makes an engine great is not how big it is, but how well all the components work together. In the case of the Shark Werks/EVOMS 4.1 flat-six, this is far better than Hans Metzger could every have dreamed when he first designed this amazing power unit.
However, there are some issues with the stock engine that EVOMS put right whenever they build an engine, whether it is one of their big displacement conversions or just a stock rebuild.
“One of these is the way the OE camshaft adjuster nut bolts unload and the unit eventually falls apart. We use pinning, different fasteners and Loctite to cure this as it is a ticking time bomb in every one of these motors,” said John.
The other weak point is coolant pipes of which each motor has eight. These sometimes come unstuck from their various housings, causing catastrophic coolant loss. Shark Werks have come up with an easy modification that overcomes this permanently.
A lesser-known problem is cracking of the moulded plastic coolant pipe elbows that go to the oil coolers on GT3 and Turbo motors. These require expensive removal of the engine to replace, so in the course of any engine build or rebuild, Shark Werks replace these with stainless steel ones that use CNC billet ends.
Outside of the motor, the clutch pressure plate rivets have a tendency to snap. Upgrading them to the OE 4.0-litre unit is the remedy. It is more expensive but worth it.
This joint project between Shark Werks and EVOMS has been spectacularly successful, with the latter handling the development work and Shark Werks looking after the marketing of the finished product in their test car.
After sampling their potent and charismatic 3.9-litre conversion two years ago, I was absolutely dying to try their 4.1. I knew I would be impressed, but I never quite expected to be so blown away by this car.
The Shark Werks/EVOMS GT3 RS 4.1 is not just one of the best tuner cars I have ever driven in my 30 years in the industry, it is also showcases the tremendous latent potential in the brilliant GT1 motor that Hans Metzger penned all those years ago.
It is also a tribute to the 997 GT3 RS chassis and PCCB brakes and Shark Werks modifications that the car still retains its exquisite balance. If anything, the chassis mods made the stock motor seem a little underpowered, but the big motor has made everything good again.
Now that the amazing 991 GT3 is on sale, there are many low mileage, well cared for GT3 RS 3.8s being traded in. So, if you prefer a manual gearbox to the new PDK system, find one of these good value hard-core drivers’ 911s and have Shark Werks build you a replica of their 4.1-litre Turbo killer.
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