We all knew it was coming, though Harley-Davidson did everything possible to hide its move toward liquid-cooling under a bushel. With the exception of the V-Rod introduced more than a decade ago, Harleys have always been air-cooled, but times, needs, governmental regulations, and rider expectations change, so despite more than a century’s worth of tradition in 2014, very quietly, Harley introduced its “twin cooled” engines.
The air and “precision-cooled” 103s debuted in a few select applications, with “precision” in that sales description being H-D quiet-speak for water. A 2011 patent revealed exactly how Harley planned on doing this, water-cooling the cylinder heads for its big V-twin. It’s a clever design using twin radiators and cooling fans well hidden inside the fairing lowers. Coolant is circulated via a small pump down at the bottom of the downtubes, and most of the plumbing is concealed between the top of the cylinder heads and the fuel tank. Taking advantage of this additional cooling for the cylinder heads, with water jackets concentrated primarily on the exhaust side surrounding the valves and ports, Harley bumped up the compression, switched cams, and dubbed the new engine a “High Output” 103. And it worked. That liquid-cooled Big Twin delivered reliable power while consistently running 20 to 30 degrees cooler than its strictly air-cooled counterpart.
“I think we’re looking at the future here,” says Jason Hanson at Speed’s Performance Plus. “In theory, if you can control cylinder head temperature, keep it down, you should be able to reliably make more power and keep that power at its peak. When a cylinder head gets hot, power always drops off some—that’s just a thermodynamic fact. Adding liquid-cooling around the hot spots of a Harley’s head, all around the exhaust valves and ports, can better control that buildup of power robbing heat.”
And Jason’s had the opportunity to test that theory. Today the liquid-cooled Harley Big Twin in both 103 and 110 versions, or the “wethead Harley” as it’s been called, is offered in a few select models of bikes and trikes, machines such as the CVO Limited, Street Glide, and Road Glide Ultra with the 110 and CVO Tri-Glide Ultra with the 103, all able to disguise the presence of those radiators in fairing lowers. And while other tuners have, so far, been hesitant to attempt performance mods on the Twin Cooled Harleys, Jason and the SPP team jumped right in. With some pretty promising results.
Not surprisingly the liquid-cooled Harleys, the 110 especially, respond to a performance touch pretty much the same way its air-cooled sibling does. The main problem, Jason has found, is once again a lack of compression. “It’s the thing holding this motor back,” he says. Harley lists it at 9.2:1, identical to the air-cooled engines. Additionally, the camshaft grind is aimed more for torque than horsepower, so a stock liquid-cooled 110 will show maybe 80 rear-wheel horsepower on the dyno with around 110 pound-feet of torque. After Jason was through with it that same bike was making 117 hp and had 121 pound-feet of torque. “And I believe that’s just the start,” he goes on. “I’m confident we’ll be able to reliably squeeze 130/130 out of these liquid-cooled engines, horsepower and torque. And still have an everyday friendly and most importantly cooling-running engine.”
The changes made? Most significantly the compression ratio was raised, up into the 10.0:1 range. Jason swapped cams, as well, slipping in a grind more suited to the bumped-up compression. Additionally, the exhaust ports were flowed and gently cleaned up and the cylinder head work was limited to just the exhaust side because these new MVA heads on the 110 are actually pretty good with just a few issues. The combustion chamber, Jason notes, is enormous, but the compression boost addresses that, and while the intake port and valve size is more than acceptable, the exhaust ports could stand a little attention and got it with the SPP wethead build. Obviously, care had to be taken here because there are water jackets surrounding those ports. Grind too much and you’ll hit liquid. Naturally a good set of pipes and a free-flowing air filter were part of the package, all followed with a custom tune. But that’s about it. More compression, the right cams, a little port work, and those intake and exhaust add-ons and the wethead Harley was growling with authority, keeping a cool head doing it. Interested? Plenty of riders already are, and more are certain to join those ranks as Harley finds a way to hide those radiators on bikes without fairing lowers and broadens the liquid-cooled applications. Either way, stop by and talk to the Speed’s Performance team about all this next time they’re close by, or give them a call.
Speed’s Performance Plus
(605) 695-1401 – MN
(605) 695-2272 – SD
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