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MD First Test: Harley-Davidson’s New Twin-Cam 96 Engine and Cruise Drive Six-Speed Transmission

Regular readers will have seen our article a few weeks ago announcing Harley-Davidson’s new models for 2007, along with the company’s new ‘Big Twin’ powerplant, the Twin Cam 96. While several of the new models are quite attractive, they are really only minor upgrades to existing machines (the only exception to this is the V-Rod VRSCX, which will be covered in an upcoming ‘First Ride’). The really big news for H-D fans is the Twin Cam 96 motor, and its companion, the Cruise Drive six-speed transmission – which will replace the Twin Cam 88 in every ‘Big Twin’-powered model in H-D’s lineup (basically everything but the Sportster and V-Rod).

As you probably guessed from the name, the Twin Cam 96 displaces 96 cubic inches, up from the 88 cubic inches of the old Twin Cam 88. For those of you who feel more comfortable with metric numbers, the TC96 displaces 1584cc as opposed to the TC88′s 1450cc – a 134cc increase.

The TC96 shares its basic architecture with the TC88, but the vast majority of its parts are new. H-D accomplished the 134cc displacement increase by lengthening the stroke of the TC96 by .38 inches (from 4.0″ to 4.38″), while retaining the same 3.75 inch bore found on the TC88. Increasing a motor’s stroke tends to provide increased torque and midrange horsepower, and H-D claims just that for the TC96 – claimed peak torque is up by as much as 11 ft-lbs over the TC88 (exact torque and horsepower outputs vary by model – different exhaust systems cause the variation).

The list of changes H-D made to turn the TC88 into the TC96 is long, so we’ll stick to the highlights:

  • The starter is now bolted directly to the inner primary housing, which eliminates the starter jackshaft, increasing reliability.
  • Internal oil passages connect the engine and transmission, eliminating the need for (unattractive) external oil lines.
  • New pistons and connecting rods are lighter than those of the TC88, which is claimed to increase performance and reduce vibration.
  • The cam chain is now tensioned by an automatic hydraulic tensioner, and the primary chain gets its own automatic tensioner, both of which extend service intervals for the new powerplant.
  • The new Cruise Drive six-speed transmission features carefully selected gear ratios for improved roll-on performance in every gear, and smoother highway cruising in sixth gear.

You can find a more complete list of the changes to the TC96 here.

So how do all the changes add up as far as real-world riding is concerned? Over the course of two days of riding in Southern California’s San Diego county, we had the chance to sample the Twin Cam 96 and Cruise Drive trans in several H-D models, including the Dyna Street Bob, Softail Custom, and Touring Street Glide – basically, we tried at least one version of each of the three ‘Big Twin’-powered H-D product lines.

Harley-Davidson’s smartest move, at least in my opinion, was the change from the old five-speed trans to the new six-speed. The increased torque of the new TC96 powerplant, combined with the better gear ratios of the Cruise Drive trans, makes itself felt immediately by way of vastly improved roll-on acceleration. The difference from the old TC88 feels much more significant than you would expect from a displacement increase of only 134cc – clearly, much of the new-found accelerative ability is a result of better gearing in the new six-speed.

Still, the six-speed can’t take all the credit – the TC96 definitely comes with a healthy helping of torque. All the TC96 powered machines, particularly the lighter Dyna and Softail versions, were extremely flexible, allowing the rider to spend long periods of time without changing gears. Whether you’re cruising through the canyons without ever leaving third gear, or accelerating from 65mph to 80mph on the highway without leaving sixth, you’ll definitely appreciate the job H-D’s designers did on this new powerplant.

We can also validate H-D’s claim that the TC96 runs smoother than the TC88 it replaces. While the signature low-frequency pulsing of Harley-Davidson’s big twins is still there, we didn’t find so much as a hint of high-frequency, hand- and foot-numbing vibration on any of the TC96-powered bikes we tested. It appears that a careful redesign allowed H-D to build the best of both worlds – keeping the ‘character’ of their classic Big Twins, while at the same time making them more enjoyable and less fatiguing on long rides.

In addition to massively benefiting the rideability and acceleration of the H-D lineup, the Cruise Drive transmission also features smoother, lower-effort shifts than the older five-speed trans fitted to the TC88. On the old trans, shifting was accomplished by moving the entire gear along a shaft – which became more difficult as the gear’s inertia increased with RPM. The solution? The Cruise Drive uses steel ‘dog rings’ that slide along a shaft, providing positive gear engagement with less effort and far less ‘clunkiness’.

Overall, the new engine and transmission greatly increase both the rideability and ‘fun factor’ of the H-D lineup, and we’re certain that buyers of H-D’s Big Twin-powered 2007 models will be happy with the improvements, especially since it comes with a relatively minor increase in price (around $500 on Softail models, for example).