Screamin' Eagle 135 Stage IV Unleashed as Harley's Largest and Most Powerful Street Engine

Shortly after releasing some new and updated motorcycles for the 2023 model year back in January, the Milwaukee-based company now rocks the industry with the release of a brand-new crate engine. And not just any engine, but one described as the largest (as in the one with most displacement) and most powerful street-compliant crate powerplant it ever created.

The unit is part of the Screamin' Eagle family, and comes tuned to Stage IV. It is officially meant for Touring motorcycles produced after 2021, but we’re pretty certain someone out there will be able to find some other uses for it as well.

Harley tells us that the Screamin' Eagle 135 was made at least partially with lessons learned from its participation in the MotoAmerica Mission King of the Baggers series. And that should tell you something, given how the competition is a fierce battle between Harley and its main competitor on the American market, Indian.

What that means, for instance, is that the engine uses a new 68 mm throttle body complete with CNC-machined intake manifold, and these pieces were initially developed for factory racing team engines. There are also new high-compression forged pistons in there, a new flywheel, and equally fresh fuel injectors.

What all of the above, and some other engineering tricks as well do is make the 135 a force to be reckoned with. As per the specs provided, the engine churns out 130 horsepower at 5,500 rpm, which for comparison’s sake is a staggering 41 percent increase over what your daily Milwaukee-Eight 117 makes. Torque is high as well, sitting at 143 lb.-ft. at 3,500 rpm.

But that’s only the start, as the powerplant can further be tweaked with a special, factory-supplied tuner tool. In fact, this is a mandatory gizmo to get the engine ready for duty once installed in the frame.

Installing the engine into an existing Touring motorcycle is not difficult, as the Screamin’ Eagle is a bolt-on affair for this kind of chassis, and it requires no modifications to be made.

Harley will make the engine available in two variants. The first is meant for post-2021 Touring models equipped with an air/oil-cooled Milwaukee-Eight engine, while the second is intended for the bikes that use twin-cooled powerplants of the same family.

Regardless of choice, the Screamin' Eagle 135 Stage IV has a price of $7,999.95, but a series of other parts (like head pipes and oil coolers) will be required to get it ready for the road, so expect the final price to be a bit higher. Depending on the visual needs, the engine can be had in either black or chrome.