Twin-Cam Monster

TWIN-CAM MONSTER

There's stil plenty of life left in Harley's air-cooled V-Twin

FOR ALL OF YOU who think that Honda now owns the big-bore V-Twin performance market with its VTX1800, Harley-Davidson has an impolite response. No, not the expected reference to bovine excrement, and not just the new liquidcooled hot-rod shown elsewhere in this magazine. No, we’re talking about the exhaust note of the nearly 1700cc

FXD the Motor Company loaned us. That FXD, fitted with the cream of Screamin’ Eagle performance accessories-including Harley’s new stroker kit-loudly announces with a full 108horse thunder that Harley is conceding nothing to anyone with its conventional air-cooled Big Twins.

At its heart spins Harley’s new stroker crank. Made for H-D’s Parts and Accessories division by well-known Harley hop-up specialist Jims Machining, the new crank has been given integrally forged flywheels and mainshafts that are then fiilly CNCmachined. These push new, highstrength (and also fully machined) connecting rods through a 4 3/8-inch stroke-3/8 of an inch longer than stock. Special stroker-only 3 7/8-inch big-bore pistons (the same diameter as supplied in Harley’s 1550cc kits) mount their wristpins higher than normal, so both rod length and cylinder deck height can remain the same as stock. Price for the crank assembly and pistons runs $1580. The combination of bore and stroke increases brings displacement from 1450cc to 169lee, or-if you’re not a metric kind of guy-from 88 to 103 cubic inches.

Almost more important, though, is that the stroker kit was subjected to Harley’s normal engine-development process. According to a Harley engineer, “We put in a lot of development and durability time to ensure a quality product. There were hundreds of hours spent on the engine dyno on an aggressive-duty cycle.” Some of that was aided by using a couple of standard parts that had themselves been part of intensive development during the genesis of the Twin Cam 88—its crankpin and big-end roller bearings. These remain the same parts as in every other TC.

Completing the package for this Dyna are Harley-Davidson Screamin’ Eagle cylinder heads, “258” camshaft, adjustable pushrods, 7000-rpm ignition module, low-restriction mufflers and two-barrel Holley carburetor kit. The result, built entirely from parts available from the Motor Company, is a machine that looks almost stock, but doesn’t perform like it. Thumb the starter, and the Dyna’s engine cranks over more slowly at first than a standard Twin Cam. Upon firing, its warm-up idle is slightly rougher than stock, and its exhaust note, even at these low speeds, is not exactly neighbor-friendly.

Click into first gear, and you find yourself riding a torque monster. Shift at 3500 rpm, and you can match the performance of a standard Twin Cam shifted at redline. It’s even easy to get in the habit of doing that, in which case you might think this bike is a pussycat. One trip to the 6000rpm power peak and beyond will dispel that, as the hot-rod Dyna lunges forward like few Harleys before it. With 106 foot-pounds of torque at 4500 rpm, and 108 horsepower at 6000 rpm, this machine can fly through the quarter-mile in the mid-11 s, do 0-60 mph in 3.0 seconds and pull roll-on times (3.4 seconds for both 40-to-60 and 60-to-80 mph) that are as good as most big-bore sportbikes. This is a Big Twin that deserves to wear an “S” on its chest.

There are just a few drawbacks. The cams installed have traded a little bottom-end power and smoothness for top-end, a little disturbing in that this stroker is averaging 5000 piston feet per minute at 6800 rpm, an

engine speed it runs to very naturally, and a piston speed normally reserved for race engines. At the introduction of the stroker kit, Harley engineering was showing another, yet stronger torque curve for a more mildly tuned version, and it still peaked at around 100 horses. We’d forgo the cams and shoot for that if we were installing this in a machine that was going to rack up a lot of mileage. And, even with the Dyna’s rubber mounts, the long-stroke engine vibrates a bit more than a stocker. Finally, there’s the exhaust note, which, while not unusual in Harley circles, is simply too loud.

But those are small costs for such outrageous performance. And, of course, this may be more than a slight hint of what the future may hold for production Harleys. The 1550cc bigbore Twin Cam kit has already made limited production in Harley’s Custom Vehicle Operation Screamin’ Eagle Road Glide. While the stroker crank is currently an accessory listed “for off-road use only,” we wouldn’t be surprised to see 103-cubic-inch production Harleys a few years down the road.

Steve Anderson