This article appeared in Racecar Engineering, The International Journal of Motorsport Technology (RCE VN18 N9).

At first glance, it is difficult to imagine improving a Porsche 996 GT3 Cup Car. If perfection was ever attainable, wouldn’t it already be close? However, Quaife’s latest “Q-Tek” (QBE61G) gearbox promises just that and offers an affordable alternative to the more traditional Hollinger or Sadev gearbox.

Like its Porsche Motorsport counter-part, the QBE61G is a six speed sequential transaxle gearbox featuring a larger than standard 85mm shaft capable of applications in excess of 500bhp and 450lb/ft torque. As standard it is supplied with a plate-style limited slip differential although Quaife’s newer automatic torque biasing differential is an optional upgrade. It features a wholly-mechanical sequential shift and internal lubrication via an integrated, internal oil pump.

Mike Quaife believes they have identified a requirement for this type of gearbox. He explains: “We could see a market amongst club and national level Porsche competitors for a more economical gearbox. It is designed within the dimensions of the original Porsche 996 meaning its integration is a straight-forward conversion.”

Indeed, they have achieved that. A race ready QBE61G, including bell housing, gearbox mounts, flywheel, triple plate Superclutch and ancillaries costs 10,950GBP (+VAT). Adding a limited slip differential brings it to a total package price of 11,900GBP (+VAT). Compare this to the equivalent Porsche Motorsport Sequential box for a not insignificant saving of 8,761GBP.

And it’s not a compromise, either: “The QBE61G achieves a 20 millisecond shift – that’s twice as fast as the standard Porsche gearbox.” explains Mike. “Infact, it’s so fast that in testing the automatic ignition disengage was disabled to make the car drivable on down shifts.”

He continues: “In testing, its reliability has been impressive. We’ve completed almost 30-hours of testing, in the UK and Spain without a single failure.”

This quality of build is underlined by its potential for further applications: Quaife offer a helical set of ratios for use on the road (and a helical gear limited slip differential) and the QBE61G could even find its introduction into GT3 endurance racing such as the LMES or FIA GT.

“Overall, we wanted to provide value for money with the QBE61G,” concludes Mike. “When you also consider its performance and reliability too, I think we even surprised ourselves.”

A Drivers Perspective

The first drive in any new car is a daunting experience. You drop the clutch, exit the pitlane and unleash to a world of uncertainty. Racing drivers perform in the subconscious – they are perfect choreographers of laps practised, performed and executed hundreds of times before. Every steering, brake and throttle input, every direction change and gear shift is rehearsed to the point that in itself, it is an almost instantaneous and automatic reaction to the changing behavior of the car or the circuit. Broadly speaking, it can be taught with seat time. However, until this point, you are very much driving with a conscious mindset.

A Porsche 996 GT3 Cup Car is about as hostile of an environment as any sports car debut could be. Reputations are built for a reason and a 420bhp 3.4-litre flat-6 mounted beyond the rear axle is along way from the nimble, mid-engined single-seaters that I am used to.

Every shift must be a positive application of the gear lever. We’re using the QBE61G-specific Quaife gear lever, designed for the 996 and I am told it is another improvement over the standard mechanism. Ergonomically, I have little doubt and the actual process of changing gear becomes natural within the first lap. The clutch feels light, probably too light, but as this test car approaches 30-hours of running, it can be forgiven.

Under heavy acceleration (and maximum load) a small breathe of throttle is all that is required to provoke a seamless and clutchless up shift. There is no significant transmission jolt and the speed of engagement means there is only a small transfer of weight and therefore wasted energy.

A drivers unfamiliarity with a car is normally most prevalent on corner-entry. The initial cornering phase involves more thought than can be consciously achieved given the available time. But such is the precision of the QBE61G that I find myself underwhelmed by the complexity of down shifting five gears in a bumpy and difficult braking area. Within no more than a lap and half I am confident that my down shifting technique, synchronised with a positive blip of throttle, is learnt and already I can become more receptive to reaching the threshold of the Porsche’s ceramic brakes.

Each and every push of the gear leaver emphasizes the elegance of this gearbox. Even a total mismatch of revs on a downshift does little to provoke the kind transmission or differential oversteer you might expect from this type of car. In fact, I would even surmise that drivers without a good heel-and-toe technique would be more than capable of driving the car at moderate to high-speed.

Perhaps, ultimately, the point is this: despite its reputation and its undeniably intimating demeanor, my first experience of a Porsche GT3 was not the learning curve I had expected. I might even go as far as to say that it is a more comfortable experience than say, a Duratec Formula Ford. If you consider the reputation it has, maybe this is difficult to accept or even understand. However, what key component was different about my first experience to that of those before me? Gearbox. And what does that tell you?

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3. Porsche 996 GT3 Test (Racecar Engineering)

The task was to sample the new Q-Tek sequential gearbox from Quaife, designed for the Porsche 996 GT3, at the Llandow Circuit 20 miles west of the Welsh capital.

Whilst it wouldn’t be appropriate for me to write too much on the subject at this point, it is fair to say that despite its somewhat intimidating demeanour, the 996 GT3 (and Q-Tek box) is amongst the easiest and is certainly the most pleasant car I have ever driven.

Read more about the test and the Q-Tek gearbox in a forthcoming issue of Racecar Engineering.

Thanks goes to Sam and Charles at Racecar Engineering and Peter, Phil and Mike at Quaife for the opportunity.

Update: http://www.racecar-engineering.com/community/raceblogs/227112/porsche-996-gt3-test.html.

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3. Quaife QTEK QBE61G gearbox, Porsche 996 GT3

This article appeared in Racecar Engineering, The International Journal of Motorsport Technology (RCE VN18 N7).

Fundamentally, motorsport is the management of risk. On the track, it is the drivers responsibility to take the risks he (or she) feels necessary, within their environment, to maximize performance and yield the best possible result. But off the track, this is an engineers job and by calculating the risks associated with set-up, electronics and engines (to name but a few), only then can the driver focus on the ultimate goal: to win the race.

As the technology on-board modern racing cars continues to increase, so does the complexity of managing it effectively. Traditional wiring looms have become cumbersome and increasingly within modern racing cars they are being replaced with CAN-bus systems. Migration will typically yield a substantial reduction in wires: the minimal configuration can contain just two (data and power) whilst potential still connecting an arbitrary number of sensors, actuators, gauges and ECUs.

CAN (or Controller Area Network) quickly became a standard in the automotive industry after its inception by Robert Bosch GmbH in 1988. However, its introduction into motorsport has proven more sedate – it featured on the first WTCC BMW (320si) in only 2006. Last year, the Power Control Module (PCM) from Ole Buhr Racing received full FIA homologation and its use is set to expand further into World Touring Cars and complement its already established position in sports and prototype racing.

What is it and how does it work?

A CAN-bus system consists of a collection of actuators and sensors (known as nodes), connected via a single twisted-pair (network) cable. CAN itself is the computer network protocol that allows these nodes to communicate without the use of a host computer. Essentially, CAN-bus connects the electronic devices on-board the car in a similar fashion to a traditional computer network.

All nodes on the network are able to transmit and receive messages. Messages carry a maximum payload of 8-bytes and are protected by a cyclic redundancy check (CRC). Within most applications (networks within 40m), transmission occurs at 1Mbit/s.

Unusually for a computer network, individual nodes are not assigned addresses. Instead, messages are broadcast to every node on the network and as such, simultaneous transmission is not possible. A scheme of bit-wise arbitration is used to determine which nodes can transmit based upon the priority of the message and the bus is always available to a node with a higher priority (or dominant) message, even if a lower priority (recessive) message is already in transmission. In which case, once the dominant message is complete and the bus becomes idle, the recessive message is transmitted again.

This bit-wise arbitration is particularly valuable in real-time environments where transmission efficiency is key and where a more common message-wise arbitration approach (such as CSMA/CD used in Ethernet) is not particularly well suited. In CAN, no bandwidth is used for any non-relevant information.

Error detection and prevention

Perhaps the most compelling features of CAN are its sophisticated mechanisms for preventing and detecting errors.

CAN is a differential serial bus which means it particularly good at reducing noise caused by electromagnetic interference (EMI). As the engine-bay of a racing car is a particularly hostile environment for EMI, this design increases the reliability of transmission and reduces the likelihood of unpredictable behavior – such as the loss of engine ignition (from the ECU).

Internally, complementary signals are sent over two separate wires and as a result, it doubles the noise immunity of the signal. This can be best expressed in mathematics.

The voltage difference of the high state is said to be , where the represents one wire, and represents the other. If these are exchanged on the low state (), then the total combined difference is expressed as and is therefore double the noise immunity of a single wire serial bus.

CAN hardware also retransmits faulty messages automatically by detecting errors at both a message and bit level.

At a bit level, two different techniques are used: bit-monitoring and bit-stuffing. Bit-monitoring is where a CAN node continuously reads back a transmission from the bus, comparing what was transmitted to what was received. If a difference exists, the message is considered faulty.

Similarly, bit-stuffing is where after five consecutive bits of the same level are transmitted, an additional sixth bit, of the opposite level, is added (but is not interpreted by the receivers). The actual purpose of this is to avoid excessive DC components but it serves as an additional means for detecting errors.

At the message level three further techniques are used: a frame check, an acknowledgement check and a CRC.
The form of a message (known as the frame check) is validated by comparing the expected sequence of bits (specified in the protocol) against the actual transmission.
Each receiving node adds an acknowledgment to the message and if this cannot be detected by the following node, the message is again considered faulty.

Finally, a basic Cyclic Redundancy Check is applied to the message bits in order to protect the integrity of the message payload.

The CAN specification also includes a slower fault-tolerance mode (below 125kb/s) which enables the bus to continue functioning in the event of the cable being damaged or even partially cut and is particularly relevant in the case of an accident or minor contact over the duration of a race. Ultimately, if a node or the cable is damaged, the network will continuing functioning (albeit at a slower speed).

Why use CAN?

It goes without saying that CAN is not suited to every environment. Although already small (197×107x46mm), Ole Buhr’s current PCM is still somewhat oversized for single-seaters. However, in LMP, sports and touring cars where space and weight is at a relative premium, its introduction is supported by good pedigree: ALMS Champions with Porsche (RS Sypder), LMP with Creation and BTCC Champions with VX Racing represent highlights from 2007.

And neither is it cheap – at almost GBP 3500+VAT, Ole Buhr Racing know its market. But in professional categories where the initial cost of components is secondary to the cost of poor reliability, it’s perfect.

In such applications, fast access to diagnostics means that CAN is the only reliable option. Instead of the time-consuming process of searching for short-circuits or faulty junctions with a voltmeter, software immediately shows the status of every node on the network and because of its architecture, nodes can be readily replaced, added or removed without any implication on other components.

The PCM also features a built-in, programmable logic controller which allows for the automation of tasks when certain conditions arise. For example, the engine could be automatically started as the car is released from its jacks.

It’s here to stay

Overall, it is the absolute simplicity of CAN which makes its use so valuable. An entire network of actuators, sensors or even switches and dials can be reliably maintained with enormous reductions in analogue wiring and therefore risk. As its application within motorsport continues to become more prevalent, the overall cost, given time, will settle. In the mean time, if you’re wondering whether adding another junction to your wiring loom is such a good idea, maybe take a closer look at CAN and what it can do for you.

References

• http://www.embedded.com/columns/murphyslaw/13000304
• http://www.computer-solutions.co.uk/info/Embedded_tutorials/can_tutorial.htm?gclid=CKON_5fTpZICFQ9BMAodRGZxMA
• http://www.sensorland.com/HowPage054.html
• http://www.obr.uk.com/Handbooks/PCM%20Handbook%20ver%20301a.pdf
• http://www.embedded.com/columns/murphyslaw/13000304?_requestid=498927
• http://www.ems-wuensche.com/CAN_technical_information.html#anchor639233
• http://www.kvaser.com/can/intro/index.htm

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