What’s the Biggest Motor Harley-Davidson Makes?

Are you a Harley-Davidson biker looking to get the most powerful riding experience on the biggest motor that the brand makes, but you don’t know which one it is? If yes, then this is the right place for you to be.

The biggest engine Harley-Davidson makes is the Screamin’ Eagle 135ci Stage IV Performance Crate Engine, offering a massive 135 cubic inches (2,212cc) of pure American V-twin muscle. Designed for performance enthusiasts, it delivers relentless rear-wheel torque and tire-shredding horsepower.

In this comprehensive guide, you will learn everything about Harley-Davidson’s largest powertrain, how it performs on the open road, what it costs to install, and how to keep your big-bore motor running smoothly for miles to come.

What is the Biggest Motor Harley-Davidson Makes?

Since 1903, Harley-Davidson has been delivering resilient, classy, and powerful bikes for avid riders. Every year, the brand introduces new models and pushes the envelope of factory engineering. Harley-Davidson shattered records with the release of the Screamin’ Eagle Milwaukee-Eight 135ci Stage IV Performance Crate Engine.

This absolute monster offers a massive displacement of 135 cubic inches (2,212cc), securely dethroning rival Indian Motorcycle’s largest stock cruiser engine—the Thunderstroke 116 (1,890cc)—to claim the crown as the largest street-compliant crate engine produced by a major motorcycle manufacturer.

The Ultimate V-Twin Displacement Comparison

The Screamin’ Eagle 135ci engine serves as a direct bolt-in replacement for 2021 and later Harley-Davidson Touring models running either Air/Oil-Cooled or Twin-Cooled Milwaukee-Eight chassis. It builds upon the legacy of the previous 131ci crate engine, introducing larger components, massive structural breathing upgrades, and track-tested reliability sourced straight from the factory’s King of the Baggers racing program.

New Features of the Screamin’ Eagle 135ci Engine

The Screamin’ Eagle 135ci engine is a complete, bottom-up build from the Milwaukee factory, meaning it is much more than a simple big-bore cylinder swap. It integrates a collection of premium high-performance components:

• Massive Throttle Body: A giant 68mm throttle body paired with a matching CNC-machined intake manifold to optimize airflow.
• High-Flow Heads: Screamin’ Eagle Extreme CNC-ported cylinder heads equipped with high-performance valve springs that remain perfectly stable at high RPMs.
• Forged Pistons: High-compression 10.7:1 forged pistons engineered to withstand intense combustion forces.
• Upgraded Fueling: High-capacity 6.8 grams-per-second fuel injectors to adequately feed the giant 2,212cc cylinders.
• Heavy-Duty Oil Pump: A Pro Billet cam plate and oil pump that maintains high pressure even when engine temperatures soar.
• Aggressive Camshaft: The SE8-517 high-lift cam, high-performance cam bearings, and high-performance tappets ensure maximum valve duration.

The engine features signature 135 Stage IV badging on the cylinder heads and the timer cover, available in either a striking black or classic chrome finish to blend seamlessly with your touring bike’s aesthetic.

How the Screamin’ Eagle 135ci Engine Performs

Going to a Harley-Davidson dealership and riding out a few hours later with a 41% increase in horsepower and a 28% jump in torque over a standard production Milwaukee-Eight 117 engine is a rider’s dream. The 135ci crate engine turns a stock touring motorcycle into a terrifyingly fast hot-rod bagger.

Stock Production Engines vs. The 135ci Monster

Standard production engines (like the Milwaukee-Eight 114) feature a standard “shed-roof” torque curve. Peak torque hits early at around 2,500 RPM, but rapidly slopes downward as higher revs outpace the engine’s breathing limits.

The 135ci engine operates on a broad “haystack” torque curve. It produces an immediate, linear rush of power, peaking at 143 lb-ft of rear-wheel torque at 3,500 RPM and climbing all the way to 130 rear-wheel horsepower at 5,500 RPM.

[Stock M8 114/117 Engine]  ---> Early Peak Torque ---> Fast Drop-off at High RPMs
[Screamin' Eagle 135ci]    ---> Massive Low-End   ---> Flat, Linear Surge to Redline

Street Acceleration and Highway Passing Power

From 0 to 30 mph, the 135ci engine feels incredibly healthy, though you will want your Traction Control System enabled to manage wheel spin. The true power gains reveal themselves past the 40 mph mark.

On the highway, while cruising at 80 mph (just under 3,000 RPM), a stock engine is already on its downward torque slope. The 135ci engine, however, keeps building momentum up to its 5,500 RPM peak. This gives you instant, roll-on passing power in top gear without ever needing to downshift.

Sound, Heat, and Fuel Economy

Pairing this motor with a high-flow intake and Screamin’ Eagle Street Cannon mufflers results in a deep, chest-shaking exhaust note. It retains the iconic, traditional Harley-Davidson rumble, but amplifies it into a crisp, authoritative roar.

Surprisingly, the extra displacement does not ruin daily rideability:

• Heat Management: Radiant engine heat stays well within acceptable limits. Liquid-cooled heads target the rear cylinder first, meaning it won’t roast your legs in heavy city traffic.
• Fuel Efficiency: While economy drops slightly compared to stock layouts, it remains exceptionally efficient given the massive performance upgrade.

The True Cost of Unleashing 135 Cubic Inches

The Screamin’ Eagle 135ci Stage IV Crate Engine carries a base MSRP of $7,999.95. However, riders should budget for the auxiliary parts required to safely run this amount of power.

To complete the installation, you will also need a separate high-flow head pipe, a fan-assisted oil cooler kit, an upgraded air cleaner, and a Screamin’ Eagle Pro Street Tuner to recalibrate the ECM. When adding these components alongside roughly 8 hours of dealership labor, the total on-the-road cost typically lands between $12,000 and $13,000.

Warranty Protection: If the engine is installed by an authorized Harley-Davidson dealership within 60 days of a new bike purchase, it is backed by the standard 24-month factory warranty. Otherwise, it comes with a standalone 12-month manufacturer’s warranty.

How to Make Your Harley-Davidson Engine Last

A high-performance V-twin requires proper care. Follow these essential maintenance steps to ensure your big-bore engine goes the distance:

Ride Regularly: Letting a high-performance motorcycle sit idle for months can cause seals to dry out and fluids to settle. Ride often to keep components lubricated.

Follow the Break-In Routine: The first 500 to 1,000 miles are critical. Keep your riding smooth, avoid dragging the engine, and vary your RPMs to seat the piston rings properly.

Regular Fluid Changes: Always swap out your engine oil and oil filter according to your owner’s manual. Premium synthetic oil is vital for managing the friction of a 135ci setup.

Service the Air Filter: A clogged or dirty air filter restricts oxygen and causes the engine to run rich, while a loose filter lets damaging debris grind inside your cylinders.

Keep it Clean: Wash your motorcycle regularly to clear road salt, grime, and debris from the cooling fins, protecting your engine from overheating.

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