Harley’s Hot-Rodding of the CVO Road Glide ST

[Hugh Janus]

Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

The King of the Baggers class presented by MotoAmerica at roadrace events has been a big success, pitting highly modified Harley-Davidson Road Glides against Indian Challengers. Horsepower numbers somewhere in the 165 to 185 range are spoken of in low tones. And these bikes, built to a minimum weight of 620 pounds, have changed a lot of minds by their ability to lay down really fast lap times.

It was high time that Harley riders remembered that, while it’s fun to be cool, it can be really big fun to be fast as well.

The Motor Company now offers its CVO Road Glide ST with the 121 HO engine—121 HO translates to 121ci (1,977cc) High Output—influencing the rear wheel strongly with a claimed 127 hp at 4,900 rpm and 145 lb.-ft. of torque at 3,000.

H-D’s 121 HO engine puts out 127 hp and 145 lb.-ft. of torque. (Brian J. Nelson/)

This engine puts aside the variable valve timing of non-ST 121 engines in favor of a camshaft with longer, race-inspired valve timing, redlined at 5,900 rpm.

To put these delicious changes in perspective, remember that for generations, Harleys have been known for their impressive bottom torque, which they needed to heave their not inconsiderable weight away from rest. Torque peaked low down, then sloped downward as the engine revved up.

The reason for this was very short valve timings, rather like those of a classic VW Beetle—almost what we were taught in high school: Intakes open at TDC, intakes close at BDC. On the other hand, having the valves open for such a short time makes the engine more and more short of breath as it revs up, trying to fill the cylinders in shorter and shorter time.  As the Interstate Highway System was built, riders could cruise at higher speeds and for longer. Keeping up with traffic has required more performance from time to time, and that has been provided by increases in engine displacement—without changing that feeling of strong bottom torque.

The original Big Twin, the EL or “Knucklehead” of 1936, had 61ci of displacement, soon growing to 74 and continuing upward ever since. Harley’s traditional feel never changed.

For on-ramp and passing acceleration, variable valve timing (VVT) has been useful. What it does is change the phase angle between cam and crankshaft as the engine accelerates, first providing the valve timing best for lower revs, then altering it as engine revs rise, shifting cam phase to what works best at higher revs.

Cam phasers just advance or retard the camshaft; they cannot vary the valve duration (number of degrees during which the valves are open) or the valve lift.

I suspect that the experience of the Harley KOTB racing team (Yes! Harley again has a factory race team for pavement racing, with permanent staff and “Harley Racing” T-shirts!) has shown ways to combine strong bottom performance with big horsepower on top. Such a cam surely opens the intakes before TDC, giving the intake process a head start, then closes the intakes significantly after BDC, giving more open time for cylinder filling.

Related: 2024 Harley-Davidson CVO Road Glide ST First Look

Tech from Harley-Davidson’s King of the Bagger racing efforts is beginning to trickle down to production models. (Brian J. Nelson/)

Another element is the KOTB-derived intake Y-manifold, claimed to flow 26 percent more air from the 58mm throttle body. Another item mentioned is an updated cylinder head. Could it be that racing still improves the breed? Could it be that higher performance still brings excitement?

Be sure also that a front pulley now with 30 teeth instead of the previous 32 increases torque at the rear wheel by 6.7 percent.

More power means more heat, continuing to underline the usefulness of liquid-cooling around the exhaust valve seats. Many problems of heat engines are caused by high temperature “creep,” which is the slow yielding of metals under stress, even far below their melting point. When the material around the exhaust valve seats and port runs too hot, creep may become a problem, loosening seat inserts or distorting/displacing exhaust valve seats. This causes valve leakage that heats the parts even more. Liquid-cooling keeps the aluminum in critical locations at safe temperatures.

Liquid-cooling is used in the heads to fend off damage to the valve seats by high temperature. (Brian J. Nelson/)

Fun does not go out of style. Seeking it is part of being human.

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[Buckster]

[Marcel le Moose Fondler]

20 hours ago, Buckster said: