Motorcycle Sport & Leisure

HARLEY-DAVIDSON’S TWIN CAM 96B ENGINE: Milwaukee Music

In launching its all-new six-speed Twin Cam 96 powerplant one year ago, an engine design marrying 21st-century technology with its traditional pushrod format, Harley-Davidson made a move arguably as significant in terms of its core product range as the replacement back in 1984 of the neo-vintage Shovelhead engine, with its cast-iron cylinders and variable build quality, by the more modern Evolution aluminium motor. Powering three of the five families of Harley-Davidson models, the Twin Cam 96 engine is rubber-mounted in the Tourer and Dyna ranges, while also available in 96B guise with a gear-driven counterbalancer for rigid installation in the Softail models, including the Rocker and Rocker C. Either way, the result has been a dramatic improvement in comfort and riding enjoyment, which ironically came as a direct spin-off from Harley’s need to address Euro 3 noise and emission requirements for its European market, which all the company’s bikes now comply with.

But meeting the Euro 3 needs of that 10%-plus of its customer base, also allowed Harley to address a variety of other concerns with a worldwide application - and especially, how to preserve the unique feel and distinctive engine note of its benchmark Big Twin models (which they’d already tried unsuccessfully to patent), while meeting ever greater legislative restrictions. They did this by making lemonade out of the lemon, and turning emissions and especially noise restrictions on their head to create the basis for re-engineering the H-D riding experience in a positive way. Meeting the new Euro 3 norms entails a greater loss in performance and especially torque the larger the cylinders of the engine in question - which is why 600cc four-cylinder Supersports all but shrug off the effects of doing so, but big twins risk ending up short of breath, as well as sounding strangled. Working under the slogan ‘Sound and Feel’, Harley engineers addressed this by creating a new motor which, while a development of the previous Twin Cam 88 design introduced in 1999, contained more than 700 new parts. Only the cylinders, pushrods, pushrod covers and a few other components were carried over from the older engine - everything else was new.

So while retaining the Motor Company’s trademark air-cooled 45-degree V-twin architecture with two valves per cylinder, for 2007 Harley increased the capacity of the existing 1450cc/88 cu.in. Twin Cam 88 to 1584cc/96 cu.in. by retaining the same 95.3 mm bore as before, but lengthening the stroke from 101.6 mm to 111.1 mm. If the result paid only lip service to the significant step up in cubic capacity which the custom cruiser class has undergone in recent years, mostly at the hands of the Japanese manufacturers with 1800-2000cc V-twins now the norm, and Triumph’s 2300cc Rocket III triple vying with Honda’s 1830cc Valkyrie six for the mantle of most massive multi, the Twin Cam 96/96B has allowed Harley to address its traditional issues of how the engine sounds and feels, while delivering improved performance versus the Japanese competition, against which it was starting to seemingly suffer, a middleweight contender against a horde of heavyweight bruisers.

So within the Twin Cam 96/96B crankcases there’s a new crankshaft assembly versus the Twin Cam 88, with lighter, shorter conrods and redesigned, less heavy pistons delivering a raised 9.2:1 compression. New camshafts deliver revised valve timing in the re-ported cylinder heads, with an uprated oil pump to enhance lubrication by 8% for the dry-sump motor. Coupled with a completely remapped Delphi ECU controlling the sequential port fuel-injection (ESPFI, in typical Harley alphabet-soup jargon), the result has been a substantial increase in torque to 117 Nm/86 ft.lbs at a lowly 3200 rpm on the Rocker and Rocker C, 70% of which is available at just 2500 rpm in an engine safe to over 6000 rpm - a remarkable achievement while still meeting the enhanced Euro 3 noise and emission regulations, which on many comparable V-twin products have caused a notable drop in grunt. Power is increased, too - depending on the model, the Twin Cam 96 produces between 64 bhp and 78 bhp, at 5300 rpm (73 bhp in the Rocker duo).

This improved performance has been harnessed by the six-speed Cruise Drive transmission introduced two year ago on the Dyna, and adopted across the air-cooled range for 2007 (except on the Sportster models) to replace the previous five-speeder, with helical gears to reduce friction and noise, and an automatic tensioner for the Regina primary chain. The ratios have been closed up to enhance acceleration, and while sixth gear isn’t an overdrive, the extra ratio means a significant 11% reduction in engine speed compared to the Twin Cam 88 when cruising in top gear on the highway, with the engine turning at a very specific 2859 rpm at 120 kph, against 3227 rpm on the old five-speeder. Softer clutch springs and a revised operating mechanism result in 7% less lever effort for your left hand, plus the Gates final drive belt now uses carbon fibre in its construction, and while 30% stronger is also narrower, helping to leave space for that 240mm rear tyre on the Rocker duo.

 

But the cleverest and most significant feature on the Twin Cam 96/96B motor is the adoption of a pair of computer-controlled valves, one each in the exhaust and intake systems, which in addition to any spinoff performance benefits are aimed at quietening the bike in certain circumstances - and by a remarkable coincidence, these correspond to the rpm and road speeds at which noise emission tests are carried out. This by definition allows Harley to run a less restricted setup outside of these parameters, which not only enhances performance compared to permanently strangled exhaust and intake systems, but also allows full restoration of The Sound, a motorcycling anthem which was in danger of disappearing under the weight of bureaucratic restriction. This may be viewed in Brussels and Washington as a cynical manipulation of environmental regulations, but to the rest of us it’s a clever way of circumventing the dead hand of officialdom, that’s completely praiseworthy. That’s because Harley has not only met EU noise and emission norms fully, while delivering a range of bikes that still sound great - the Sound of Music, Milwaukee-style, has been fully restored - but have actually gone further than what was required of them, by silencing the bikes in an urban context, over and above what noise emissions rules dictate. So, no more being woken from your sleep by the shotgun blast of a Big Twin being fired up from cold by the guy in the motel room next to you - but out on the highway the sound of thunder rolls harder and deeper than ever of late. Harley’s engineers deserve a pat on the back for squaring an improbable circle - OK, make it beers all round, instead, guys....!


• Active intake and exhaust system

They did this by installing a butterfly valve in the lower of the two separate exhausts on each bike (the emissions catalyst is in the other), as well as a flap-valve in the air filter intake duct. These solenoid-operated devices are linked and controlled by the Delphi ECU, which in addition to its normal engine management function, has what must be an extremely complex additional programme mapped to operate these valves according to a variety of parameters - engine revs, road speed, throttle opening and gear selected. So fire up the engine from cold on the automatic choke and blip the throttle at rest, and you may be surprised at how muted the Big Twin sounds as you relish its lilting idle. Get the show on the road, and at part-throttle in lower gears running at slower speeds, the ECU will figure you’re in an urban environment, so makes the valves work in concert with one another to muffle the sound of the Twin Cam 96 motor - depending on the mapping, either one valve or the other will shut, or sometimes both. Mapping this intricate system can’t have been the work of an instant, but the benefits become apparent on the open road, or in higher gears and/or wider throttle openings. Then the trademark sound of rolling thunder makes itself heard big time from the twin staggered, shorty exhausts, coupled with the intake roar from the big air cleaner on the right of the bike - together, the unmistakeable signature tune of a horny Hog hitting the highway, hooves hastening as it heads towards the horizon. Milwaukee music....

 

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