The first-gen Bronco left the factory with five engine options across its eleven-year run. The early trucks were underpowered by modern standards — Ford slotted in compact car engines to keep weight down and the platform affordable. The good news: the Ford small-block parts supply is enormous. Whether you're keeping the original engine running or planning a swap, the support is there.
Factory Engines
The original six — reliable and underpowered
Ford's compact 170 cubic-inch inline-six came from the Falcon parts bin. It produced around 105 horsepower — acceptable in 1966, marginal now. It's surprisingly reliable and parts are still findable, but if you're buying a '66 Bronco you're likely keeping it original for collector purposes, not to drive hard. Don't expect to pull hill grades without patience.
More displacement, still a slow truck
The 200ci six replaced the 170 as the standard engine for most of the production run. It brought output to around 120 horsepower — an improvement, but the Bronco still isn't quick with this engine. The 200 is a durable, low-maintenance six that rewards steady highway driving. It handles the trail fine at moderate pace. It just won't surprise you with power.
Rev-happy and underrated
The 289 small-block is the option most buyers overlook. Ford's high-revving compact V8 produces real power — around 200hp in Bronco tune — and it's naturally balanced. The 289 rev character feels more responsive than the torquier 302 at lower throttle positions. Parts are plentiful (shared with early Mustang and Falcon). If you find a Bronco with a clean 289, don't let anyone talk you out of it.
The sweet spot — parts everywhere, honest power
The 302 Windsor became the dominant V8 option when Ford introduced it in 1969, and it remains the most practical original engine to own. Aftermarket support is comprehensive — carburetors, manifolds, heads, ignition — everything is still manufactured and stocked. A healthy 302 puts down 200–220hp in stock form with room to grow. Pre-1972 versions have higher compression and breathe better. This is the engine the platform was built around.
The performance choice — torquey, heavier
The 351 Windsor shares its block architecture with the 302 but adds 49 cubic inches of displacement. The result is meaningfully more torque — better suited to trail work where you want pulling power rather than high-rpm performance. The 351 is slightly heavier, which affects nose weight on an already front-heavy truck. Worth it for serious wheeling builds. Pre-emissions examples (pre-1972) are the ones to seek.
Swap Options
The small-block Ford engine family makes the early Bronco a swap-friendly platform. The same mounts that held a 302 will accept a larger Windsor with minimal modification. Modern EFI conversions have matured significantly — reliable, documented systems are available for all common swaps.
5.0 HO (Fox-body Ford)
The fuel-injected 5.0 HO from 1986–1995 Mustangs is the most common budget swap. It drops into the Bronco engine bay with minor bracket modifications, produces 215–225hp in stock form, and supports the full range of aftermarket modifications. Wiring can be simplified with a standalone harness from companies like Painless Wiring or Fuel Air Spark Technology. This is the workhorse swap — proven, affordable, and well-documented in Bronco forums.
EFI 302 conversion
If you're keeping a factory 302 but want modern fuel injection, a TBI or multi-port EFI conversion gives you the best everyday driveability. Cold starts, altitude compensation, and consistent fueling replace the carburetor's quirks. Edelbrock, Holley Sniper, and FiTech all offer bolt-on EFI systems designed for small-block Fords. This approach preserves the original engine while solving most of the carb's real-world problems.
Coyote 5.0
The 2011-and-newer Coyote 5.0 (420–480hp depending on generation) is the prestige swap — more power than most early Bronco drivers will ever use, but genuinely transformative. It requires crossmember modifications, a transmission adapter (T56 or TREMEC TR-6060 is common), and a complete standalone engine management system. Budget $12,000–$20,000 for the swap alone before installation. The result is a truck that drives unlike anything else in the segment. Worth it if the budget allows; overkill for most drivers.
Verdict
A clean 302 or 351W is the right engine for most builds — proven, supported, and honest. The 5.0 HO swap earns its place on trail-first builds where budget exists. The Coyote is spectacular and expensive; know what you're getting into before you commit.
Carb Tuning and Altitude
If you're keeping a factory carburetor, plan to rebuild it regardless of condition. The stock Autolite/Motorcraft carbs run lean from the factory on emissions-era trucks and lean further as jets wear and float levels drift. A carb rebuild kit runs $25–$60 depending on the application — do it before diagnosing any running problems.
Altitude note
At elevation above 5,000 feet, carbureted engines run progressively rich as air density drops. Re-jetting for altitude makes a real difference — typically 2–4 jet sizes smaller for every 3,000 feet above sea level. If you're in the desert Southwest, Colorado, or anywhere with regular high-altitude driving, this matters.
Cooling System
Worth knowing
The factory radiator is marginal with a V8, especially in stop-and-go or trail conditions. An aluminum three-row radiator from a Bronco-specific supplier is a straightforward upgrade that resolves most overheating issues before they start. Budget $350–$550 for a quality replacement. If you're doing a swap, plan for a new cooling system from the beginning.