How much horsepower does a 1971 426 Hemi have?
The 1971 426 Hemi was rated at 425 horsepower (gross), with about 490 lb-ft of torque. This figure is the iconic figure most enthusiasts associate with Mopar’s legendary big-block Hemi from that era.
In this article, we explore what that horsepower number meant at the time, how it was measured, and how those figures fit into the broader history of American muscle cars. You’ll also see how modern measurements compare to the original rating and what to expect when evaluating a 1971 426 Hemi today.
Context and the rating method
During the 1971 model year, horsepower ratings were calculated using SAE gross standards. Gross horsepower measures engine output at the crank under controlled laboratory conditions, without factoring in power losses from accessories, exhaust, or the vehicle’s drivetrain. Because of this, the published numbers from that era tend to be higher than what you’d see on a modern dyno run using SAE net ratings. The 426 Hemi’s 425 hp figure reflects that vintage gross standard, which remains a key part of why the engine is so celebrated.
Numbers you should know
Below are the central figures that define the 1971 426 Hemi’s official performance, and how they relate to today’s measurements.
- Official rating: 425 horsepower (gross) at roughly 5,000 rpm.
- Torque: about 490 lb-ft (gross) at around 4,000–4,400 rpm.
- Net horsepower: not the rating used for the 1971 Hemi; if converted to SAE net (as modern testing does), the figure would be lower and dependent on measurement setup.
These numbers underscore the Hemi’s position as a peak-performance engine of its era. While the gross rating emphasizes peak output, real-world performance would vary with tuning, exhaust, induction, and condition. The transition to SAE net horsepower in later years generally reduced published numbers to reflect drivability and accessory losses more accurately.
Additional context on testing and interpretation
When enthusiasts discuss the 1971 426 Hemi today, it’s common to encounter two perspectives: the historic gross rating that Mopar published, and modern net or dyno results that reflect current testing methods and engine condition. Reproduction or restored engines can produce results that differ from factory figures due to compression, cam timing, exhaust configuration, and carburation. If you’re evaluating a real example, ask for the provenance of its build, wiping the engine surface, and any dyno or professional test data.
Summary
The 1971 426 Hemi delivered a historically iconic 425 horsepower on the books, using the gross SAE rating of the period, with about 490 lb-ft of torque. This reflects Mopar’s bold approach to performance in the early 1970s. When comparing to today’s measurements, remember that modern net horsepower figures typically run lower, and the true-in-use performance depends on numerous variables beyond the original factory rating.
What is the true horsepower of a 426 Hemi?
But what truly set it apart was the legendary 426 HEMI V8 under the hood. Rated at 425 horsepower and 490 lb-ft of torque, this monster engine made the Challenger a street-legal race car.
How much horsepower does a 1971 Challenger RT 426 Hemi have?
Displacement: 426 cubic inches. Bore and stroke: 4.25 x 3.75 inches. Compression ratio: 10.2:1. Horsepower: 425 @ 5000 RPM.
Was the 440 faster than the 426 Hemi?
The **440 Six-Pack was often faster in stock form, particularly in the quarter mile, but the 426 Hemi had a higher potential for power when modified. Stock 440 Six-Packs generally had better out-of-the-box performance due to how they were tuned and how they hooked up from the line, while the Hemi was a detuned race engine that could be built to produce significantly more power than the 440 with modifications.
You can watch this video to learn about the history and impact of the 426 Hemi: 1mIts Just Cars!YouTube · Jul 31, 2025
| Feature | 440 Six-Pack | 426 Hemi |
|---|---|---|
| Stock Performance | Often faster in stock form (e.g., quarter-mile drag racing). | Slower in stock form compared to the 440 Six-Pack. |
| Power Potential | Lower power potential than the 426 Hemi when both are modified. | Higher power potential when modified, especially with race-spec builds. |
| Factory Advantage | Lower factory-rated horsepower but with better street-tuned performance. | Higher factory-rated horsepower but often struggled with traction in stock form. |
| Engine Design | Wedge head engine. | Hemispherical head engine with larger ports and valves. |
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How much horsepower does a 1971 HEMI have?
Second generation: 426 1964–1971
| 426 Hemi | |
|---|---|
| Cooling system | Liquid-cooled |
| Output | |
| Power output | 425 hp (317 kW) (Gross) 350 bhp (261 kW) (Net) |
| Specific power | 60.9 hp (45 kW) per liter |
