Harley-Davidson’s iconic motorcycles have been around for over a century, and riders love the designs and the distinctive rumble of Harley’s legendary engines. Even though bone stock engines provide enough power to push HD’s bikes down the road quickly, riders are always looking for ways to boost the performance of their bikes. That’s where the new 135 cubic-inch crate performance engine enters the picture. Here’s everything riders need to know about the engine and its performance benefits.

 

A Little History

 

Not all Harley riders know much about the history of the brand’s legendary 45-degree twin engines. The first Harley-Davidson bike boasted a single-cylinder engine that delivered 3.9 HP. That engine roared onto the scene in 1903. However, the Harley brothers and Arthur Davidson quickly determined a power boost was needed and introduced the brand’s first v-twin in 1909. That was the beginning of the brand’s reliance on v-twin engines.

 

Improvements were made over the years as the Flathead and Knucklehead models boosted power to roughly 52 to 55 HP, but riders always wanted more. The Panhead and Shovelhead engines pushed the power levels up to 70 HP, which was an improvement, but riders demanded more, especially since Japanese and European models routinely topped HD’s standard horsepower and torque ratings.

 

The Evolution (or EVO) engines provided roughly the same horsepower but ran smoother, cooler, and more efficiently than earlier Harley-Davidson engines. Those engines powered larger HD bikes through 1999 and proved reliable. EVO engines continued to power the Sportster models for a few more years.

 

This is where the performance picture gets murkier. The next generation of engines was the Twin Cam model. The Twin Cam 88 pushed out a maximum of 62 HP from the factory. The 96 saw a boost to a max of 66 HP. Following that, the 103 provided up to 75 HP. The final engine in the Twin Cam generation, the 110, pushed the maximum rating to 90 HP. Throughout all those generations, riders everywhere found exciting ways to push their bikes’ power levels to new heights, but they were limited, to some degree, by the basic design of the HD v-twin.

 

The Revolution engines arrived on the scene next. They were used on the V-Rod, Night Rod, Street Rod and VRSCSE Screaming Eagle V-Rod. That engine produced up to 125 HP from the factory, which was a significant power increase over the Twin Cam models. The Screaming Eagle iteration pushed the Revolution’s power to a segment-leading 165 HP. However, the Revolution’s 60-degree V-twin didn’t produce the same iconic rumble Harley riders loved, and even though the power ratings were pretty astounding, bikes with that engine didn’t sell like the 45-degree twin models.

 

Next, HD enthusiasts were treated to the Milwaukee-Eight engines. The “eight” refers to the engine’s eight valves, which helped to boost performance levels, with the Milwaukee-Eight 131 model boasting up to 115 HP in its stock factory configuration.

 

Screaming Eagle Performance Kits

 

Newer Harley-Davidson models proved to be successful right out of the box, but, as usual, riders wanted more. The Screaming Eagle performance kits delivered additional power, which riders quickly grew to love. The kits came in Stage 1 through Stage 4 levels, with each level adding more speed goodies. We’ve come to the latest iteration from Harley—the Screaming Eagle 135 Stage IV crate engine.

 

If you’re considering dropping the cash for a Screaming Eagle 135 crate engine, be aware it won’t fit all models. When shopping for used motorcycles, ask about compatibility issues to ensure the model you’re considering will accept the engine.

 

How Much Horsepower Does a Harley 135 Crate Engine Have?

 

Remember that the previous top-rated HD Screaming Eagle Crate engine, the 131, was rated at 121 HP when used with other bolt-on accessories. That engine was designed to fit 2017 and later Harley-Davidson touring bikes. The 135 crate engine, on the other hand, produces a ground-thumping 130 HP and 143 lb-ft of torque at the rear wheel. That’s a significant boost over the 131 crate engine and points out the power potential of the legendary Harley v-twin design.

 

How did HD manage to generate that much power with the new design? Many minor changes contribute to the new horsepower rating, but the main ones include a high-performance camshaft and redesigned cylinder heads. Of course, the increased displacement is the result of a larger bore and longer stroke than the older 131 crate engine.

 

The increased horsepower and torque mean that riders can access instant power with a simple twist of their wrist and accelerate from a dead start or easily pass other vehicles. According to data from HD, the engine achieves maximum torque at 3,500 RPMs and top horsepower at 5,500 RPMs.

 

Check Out the Details

 

Harley-Davidson also lists several improvements contributing to the performance of the Screaming Eagle 135 crate engine. According to a recent article, those enhancements include:

 

• A new, larger throttle body and improved intake manifold to push more fuel and air through the engine and do so efficiently. 

 

• New cylinder heads improve fuel flow to the cylinders, which boosts power and increases torque. Little things like better valve springs also improve the engine’s overall performance during hard riding.

 

• The redesigned oil pump maintains higher oil pressure even when the oil is hot. That’s a major plus, as wear is minimized when lubrication is improved. 

 

• New pistons, camshaft and bearings, and cylinder sleeves all help to ensure the new engine will provide the service that Harley owners demand. 

 

• High-capacity fuel injectors round out the improvements.

 

Harley-Davidson also recommends using engine-matched exhaust and air filter components to round out the package.

 

What Bikes Will the Screaming Eagle 135 Crate Engine Fit?

 

The new Screaming Eagle 135 crate engine is designed to fit all 2021 and newer Harley-Davidson touring models. There are two versions of the engine, which means you’re covered for both the air and oil-cooled Milwaukee Eight or the twin-cooled Milwaukee Eight. The design team’s efforts mean there are no special requirements for updating to the 135 crate engine. The one exception is that the engine won’t fit HD trikes, which is sure to disappoint riders of Harley’s three-wheeled models.

 

Can Owners Handle the Upgrade Themselves?

 

A lot of Harley owners enjoy working on their bikes, but most don’t have the qualifications or equipment required to replace the engine. That’s a job best left to factory-trained experts equipped to complete the update quickly and without creating any performance issues later.

 

At the same time, bike owners may find the experts recommend updating other driveline components. The extra power the Screaming Eagle 135 engine delivers will strain the belt, but dealers providing upgrades should have the required parts on hand. If you’re unsure which parts should be upgraded during the engine swap, ask the experts at HD for advice.

 

Remember that the new engine must be fitted with appropriate emission control devices to remain street-legal, and ECM calibration is required. That’s not something most owners can do themselves, which is another reason to leave the upgrade to the experts.

 

One other thing to consider is that the engine was initially designed for track use, which means the proper steps must be taken to ensure the components used will be legal for street use. The installation team at your local Harley-Davidson dealership will know what’s necessary to make sure bike owners don’t run into legal complications later.

 

How Much Does the Screaming Eagle 135 Crate Engine Cost?

 

This is the part that starts to hurt. The crate engine retails for a lofty $7,999.95, which certainly isn’t cheap. However, many Harley owners feel the extra horsepower and torque are worth the expense. That price doesn’t include installation, which takes several hours. When discussing the upgrade with your Harley service team, ask about their labor rates and how long the job will take to get a solid picture of the actual upgrade cost.

 

Don’t forget to ask about any extra parts that are needed to complete the installation. For example, 

a new head pipe is required, and an oil cooler fan will be needed for some models. An upgraded air filter and exhaust may be on your list, and don’t forget about moving up to a heavy-duty drive belt.

 

Enjoy the Performance Boost

 

Once the installation is complete, bike owners will enjoy a level of power most riders only dream about. While upgrading to a Screaming Eagle 135 crate engine requires a hefty investment, the results will make the effort worthwhile. Remember that upgrading a bike is an ongoing adventure, so consider your ultimate riding goals when deciding how to improve your Harley.

 

Get started by discussing the upgrade with your HD technician. Find a technician that has the training to complete the Screaming Eagle upgrades, as having a top mechanic in your corner will be an absolute must. Ask the technician for advice on how and when to take care of routine maintenance. The Screaming Eagle 135 is special, and you’ll want to do everything possible to keep it running for years to come.