A key attribute of classic British sports cars like the 2014 Jaguar F-Type is the way they sound and the way they feel to drive.
While Jaguar has made impressive strides in the car's design, with an all-aluminum structure that provides a tremendously rigid foundation, company engineers recognized the risk of technical excellence is making an otherwise fabulous car too antiseptic. So they roughened up the F-Type’s edges a bit by focusing on its exhaust note.
Replicating the much-revered rasp of the iconic E-Type, however, is a challenge within the context of stringent noise and emission regulations. That ideal 1960s sonic quality is especially tough to achieve on direct-injected engines like the F-Type's supercharged 3.0-L V6 and 5.0-L V8, when virtually every hydrocarbon molecule entering the combustion chambers is accounted for and matched to a corresponding bit of oxygen.
Jaguar’s solution? Introduce some extra, unnecessary fuel and a bit of spark late in the combustion cycle to light off some crackle in the exhaust pipe. The aural effect is like a string of firecrackers dropped down a manhole, particularly on overrun. Certainly there’s a similar degree of juvenile delinquency involved in both activities, but customers don’t pay the $92,000 base price of the F-Type V8 S with the goal of being buttoned down.
Calibrating a "controlled misfire"
"'Theater' is a great word," noted Kevan Richardson, Program Manager for Jaguar sports cars. “We want the car to be entertaining. That’s why it has pop-up [HVAC] vents, a lighting cascade on start-up and a pop-up rear spoiler. It is all part of the show."
"All of those little noises are usually the kinds of sounds engineers spend months trying to dial out," he acknowledged. "Because this is an unashamed sports car, we’ve recognized the noise the exhaust makes is part of the experience and something customers want."
Jaguar engineers achieved this by defying convention. "Usually you’d cut the fuel to the cylinders, when the driver lifts off the accelerator," explained Andrew Lowis, the Gasoline Calibration Manager for the car. "We are delaying the point when we do that and igniting later than we might in normal circumstances. It produces a controlled misfire."
Obviously, the car must still meet emissions regulations despite the intentional introduction of pollutants to the exhaust stream. "It is a challenge, but it is one we can achieve by careful calibration," said Lowis. In fact, Jaguar has more stringent internal emissions limits than the government applies, he said, and the car meets those, too.
Regardless of the difficulty, it was necessary work, Lowis insisted. "The powertrain sound quality of this car was absolutely fundamental to the character of the F-Type."
The burble through the pipes is made more audible by the use of muffler bypass valves that open to send the glorious noise directly out the back when the driver selects the appropriate drive mode and stands hard on the gas or lifts off abruptly. The bypass is standard equipment on both the V6 S and V8 S, and is an option for the base V6 car.
Cleverly calibrated 8-speed
The rise and fall of the exhaust sound is also dependent on how the car changes gears, an event that with the F-Type's ZF 8HP 8-speed planetary automatic can have a disappointing "flat" character.
Here too, the solution is in careful calibration. "We feel that we’ve got the best handle on how to get the maximum performance out of a ZF transmission," said Lowis.
While dual-clutch transmissions are a recent trend among sports car makers, Jaguar engineers insist that the planetary automatic matches them for gearchange speed. However, Lowis declined to share data for this metric with AEI. "It is hard to compare because it depends where you judge the shift element to begin and end," he said. "When we benchmarked our car with a DCT, we were comparable in shift time."
Regardless, the car is certainly comparable in shift character, with the locker-room-towel-snap of ignition interrupt on upshifts and a computer-controlled throttle blip on downshifts contributing to the drama.
Above parking-lot speeds the transmission is directly engaged, providing the immediate response to throttle changes sports car drivers want. But at lower speeds the ZF transmission gives the familiar forward-creep feel at idle that drivers prefer, with none of the embarrassing propensity to roll backwards on hills that dual-clutch transmissions can suffer.
In automatic mode, the ZF is programmed to hold a gear when accelerating through a corner. It also performs rapid downshifts while braking for corners, with the engine’s management system automatically blipping the throttle to match revs. This further cultivates the F-Type’s impressive “theatrical” performance, flattering the driver in the process.