The shocking truth behind Mopar bulletproof 225 Slant Six engine

Discover Mopar bulletproof Slant Six engine, in a must watch video! Learn about the history and controversy surrounding this legendary power plant.
Witness a classic mopar moment as a seemingly ordinary $500 Dodge Dart achieves an upset victory against a big block Chevrolet Camaro
the story of the ultimate sleeper, showing how a seemingly unassuming slant six could dominate in a drag race. Witness this classic mopar, proving that you don't need flashy American muscle cars to achieve victory.

perhaps the greatest engine ever
Mopar Slant Six lies in its legendary reputation for being nearly indestructible—a result of deliberate engineering, surprising performance options, and extreme real-world durability that far surpassed expectations for a humble straight-six.


Why the Slant Six Was “Bulletproof”

Unique Slanted Design: The block was tilted 30 degrees, lowering the engine’s center of gravity, enabling a low-profile hood, and allowing a long intake manifold to improve fuel/air mixing. This design also improved engine bay space and accessory access.

Overbuilt Internals: Featuring robust tin-plated alloy pistons, thick cast iron construction, and forged crankshafts, the engine could survive poor maintenance and abusive conditions, outlasting both cars and trucks it powered. Taxi fleets, police departments, and industrial operators ran them over hundreds of thousands of miles—even with skipped oil changes and minimal care.

Efficient Cooling and Lubrication: The slanted setup moved the water pump for improved cooling. A deep oil pan ensured consistent lubrication, even on steep hills or under harsh use.

Legendary Reliability: Mechanics told stories of Slant Six engines running “years past oil change intervals,” starting with barely any coolant, and refusing to die in junkyard tests. This engine developed a reputation for running regardless of neglect, something few competitors could match.

Performance Potential: While most units shipped with modest single-barrel carburetors for economy, the factory offered high-performance "Hyper-Pak" packages for racing—featuring aggressive camshafts, headers, four-barrel carbs, and domed pistons. These modifications let the Slant Six out-power many small V8s of the time, shocking enthusiasts and outpacing even Hemi engines in select races.

Missed Opportunities: Despite its durability and hidden performance, Chrysler dropped possible upgrades (like an aluminum high-swirl head and a bigger block) due to cost and market changes, leaving the full potential of the engine mostly untapped.

The Slant Six’s Reputation
Chrysler Slant-6 engine with Clifford intake manifold and valve cover, featuring a reproduction Hyper-Pak intake
Chrysler Slant-6 engine with Clifford intake manifold and valve cover, featuring a reproduction Hyper-Pak intake

Its ability to survive neglect, abuse, and extreme conditions—including war zones and desert applications—earned the Slant Six “bulletproof” status among mechanics and racers. In short, it was an engine built not to die, shaming many more glamorous rivals and surviving long after most cars had rusted away



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Corporate Conflict
V8 executives vs. Weertman’s team (Anderson interview, Car Craft 1990).
Hyper-Pak canceled to protect V8 sales (Hoover interview, Mopar Muscle 1991


Leaning Tower of Power"* (SlantSix.org forums, 2005).
"Rebuild it with a screwdriver"* (@MoparMike, 2023).


Accuracy Fixes:
Aluminum block was prototyped but scrapped (not production).
Hyper-Pak made 196 hp (225ci), not base models.
Australian Hemi-head: 165 hp (170ci), not 225ci.



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