The Chrysler 426 HEMI is a 7,015 cc, V8 petrol engine produced between 1964 and 1971. It features a cast iron block and heads, with a true hemispherical combustion chamber design and dual overhead rocker shafts actuating two valves per cylinder. In street-legal "Street HEMI" form it delivered 425 hp (317 kW), while race versions exceeded 500 hp, making it one of the most powerful American production engines of its era.
Fitted to iconic muscle cars like the Dodge Charger, Plymouth Road Runner, and Dodge Super Bee, the 426 HEMI was engineered for dominating drag strips and NASCAR ovals. Emissions compliance for its production period was minimal, meeting only basic 1960s US federal standards through simple carburetion and exhaust systems.
One documented service concern involves valve train maintenance complexity due to its dual rocker shaft design. While not a "failure" per se, this architecture requires precise adjustment and specialized tools, as detailed in Chrysler's Factory Service Manual. The engine was discontinued after 1971 due to tightening emissions regulations and insurance pressures, succeeded by lower-compression wedge-head V8s.
Production years 1964–1971 meet pre-regulation US Federal emissions standards (No EPA Engine Family designation applicable).
The Chrysler 426 HEMI is a 7,015 cc V8 petrol engine engineered for high-performance muscle cars (1964-1971). It combines a true hemispherical combustion chamber with dual rocker shafts to deliver explosive power and high-RPM capability. Designed before modern emissions regulations, it prioritized raw performance over environmental controls.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 7,015 cc | |
| Fuel type | Petrol | |
| Configuration | V8, OHV, 2 valves per cylinder, dual rocker shafts | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 4.25 in × 3.75 in (108.0 mm × 95.3 mm) | |
| Power output | 425 hp (317 kW) @ 5,000 rpm (SAE gross) | |
| Torque | 490 lb‑ft (664 Nm) @ 4,000 rpm (SAE gross) | |
| Fuel system | Dual 4-barrel carburetors (Carter AFB) | |
| Emissions standard | Pre-regulation (1964-1971) | |
| Compression ratio | 10.25:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Gear-driven camshaft | |
| Oil type | SAE 10W‑40 (non-detergent recommended for break-in) | |
| Dry weight | 680 lb (308 kg) |
The HEMI's hemispherical chambers and dual rocker shafts deliver exceptional high-RPM power but require meticulous valve train adjustment using specialized tools. Its gear-driven camshaft is robust but noisy. The engine demands high-octane leaded fuel (or modern equivalents with additives) to prevent detonation. Cooling system capacity must be adequate for high-load conditions. Maintenance is complex and best left to specialists familiar with vintage Mopar engineering.
Oil Specs: Original spec was non-detergent SAE 10W-40 for break-in, then detergent oil (Chrysler Owner's Manual 1966). Modern high-zinc (ZDDP) oils are recommended for flat-tappet cam protection.
Emissions: No formal EPA emissions standards existed for 1964-1971 production (EPA established 1970).
Power Ratings: Rated under SAE gross (engine-only) standards, not modern SAE net (installed) standards (Chrysler Power Catalog 1966).
Chrysler Factory Service Manual (1966 Edition)
Chrysler Engineering Report 426-01
Chrysler Power Catalog (1966)
EPA Historical Emissions Regulations
The Chrysler 426 HEMI was used exclusively in Chrysler Corporation high-performance vehicles with longitudinal mounting. This engine was a premium, low-volume option for Dodge and Plymouth muscle cars, featuring unique engine mounts, suspension, and drivetrain components. No licensing partnerships occurred. All specifications are documented in OEM service literature.
Locate the engine code stamped on a machined pad on the front, passenger-side of the engine block, just below the cylinder head (Chrysler Service Manual 1966). Genuine 426 HEMI blocks also have "HEMI" cast in large letters on the side of each cylinder head. The intake manifold is a unique aluminum cross-ram design for dual 4-barrel carburetors. Critical differentiation from the 426 Wedge: The HEMI has spark plugs entering the head at an angle from the sides, not vertically from the top. The valve covers are also uniquely shaped with a pronounced hump.
The 426 HEMI's primary reliability consideration is its complexity and fuel requirements, not inherent design flaws. Its valve train demands expert adjustment, and running on low-octane modern fuel without additives risks severe engine damage. Chrysler factory documentation emphasizes precise maintenance procedures to ensure longevity, making adherence to these protocols critical for preserving these valuable engines.
Analysis derived from Chrysler factory service manuals (1964-1971) and historical technical publications. Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about CHRYSLER 426-HEMI.
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