The 426 Hemi Engine is known throughout the muscle car world. Car enthusiasts of all brands know about the Hemi and sometimes wonder why it’s so legendary. Let’s start by answering, how much horsepower and torque does a 426 Hemi have?
The 426 Hemi street engine was rated at 425 horsepower at 5,000 RPM and 490 foot pounds of torque at 4,000 RPM. It was available from 1966 to 1971 and maintained those horsepower and torque numbers every year.
This article will dive deeper into the horsepower and torque numbers. Most people are aware the car manufacturers were under reporting the power numbers of engines. Let’s take a closer look at this and find out how much power the engine really had.
The following 426 Hemi specifications and facts were learned from my personal experience and research, Mopar engine manuals and brochures, webinars, books, videos and articles.
426 Hemi Horsepower and Torque Numbers
Two of the most asked questions about a muscle car is how fast it is and how much horsepower do you have?
Not everybody can answer that question, even about their own car. How about a 426 Hemi car? The following table shows the horsepower and torque numbers of a 426 Hemi engine.
|Power Category||425 Street Hemi|
Horsepower and Torque Numbers
|Horsepower||425 Horsepower @ 5,000 RPM|
|Torque||490 Foot Pounds of Torque @ 4,000 RPM|
We all know the more power an engine has the faster the car will accelerate. The power numbers are enough to plant you and your passengers into the seat when the gas pedal is floored.
The design of the head is largely responsible for the horsepower the engine puts out. Its camshaft is relatively small compared to the ones Chevy was installing in their big block monster engines of the day, but they weren’t faster. The engine’s head made up the difference.
Even today, the Top Fuel dragsters still use the Hemi design. That alone speaks volumes for the engine and why every gear head with one wins the bragging rights.
How Car Manufacturers Underrated Power Numbers
It is common knowledge the car manufacturers of the muscle car era reported horsepower and torque numbers well below what the engine really produced.
There are many reasons why this myth exists including the following:
- Car insurance premiums.
- Some people speculate manufacturers underrated horsepower to qualify for more competitive race classes within the NHRA.
When car manufacturers starting increasing the horsepower of their motors and installing them in smaller cars, insurance companies took notice.
All insurance is based on risk, therefore car insurance companies placed higher premiums on big horsepower cars.
This can hurt the sales of some muscle cars. To enjoy the adrenaline rush of hearing 1,250 cfms rushing through 8 barrels, it was going to cost more money.
The higher premiums in addition to the cost of a Hemi option and gas maybe was too much for some people. Therefore why not stick with the 383 instead?
A way around this was for manufacturers, like Chrysler, to report lower horsepower and torque numbers.
Back in the 1960s Nascar and drag racing played a huge part in car sales for the major car manufacturers. After all, the street Hemi was born in 1966, so Nascar would allow racers to use the Hemi engine again after being banned in 1965.
The NHRA placed cars into different categories based on weight and horsepower numbers. The NHRA, like Nascar, was important to the automotive manufacturers and their sales.
The lower horsepower numbers benefited companies like Chrysler. Therefore, it’s not a myth the manufacturers underrated horsepower. I think the myth is people think they lied about it. I don’t think they did.
If they didn’t lie, how would they report lower horsepower and torque numbers?
Car manufacturers rated horsepower and torque at lower a RPM even though they produced more horsepower at higher a RPM. You’ll see in just a few paragraphs how this is true.
Another way was how they tested the engines. Adding an air cleaner and failure to fine tune, the untuned timing or air fuel mixture could keep horsepower lower.
How Much Horsepower a 426 Hemi Really Has
The 426 Hemi was rated at 425 horsepower at 5,000 RPM. 5,000 RPM is a low engine speed especially for the Hemi.
The cylinder heads allowed the engine to breathe better than most engines. So, common sense would think the engine produced more power above 5,000 RPM.
It’s common knowledge now, through many proven dyno pulls, the engine produced more power past 5,000 RPM. Actually it increases horsepower all the way to about 5,900 to 6,100 RPM.
The street Hemi also produced a few more horsepower at 5,000 RPM than what the factory reported. This may be because the factory didn’t want to fine tune the carbs or timing, limiting the power.
Let’s examine some dyno pulls on the engine and the kind of horsepower and torque they are really putting out.
Check out how much horsepower the Hemi engines produced prior to the 426 had in my article, Hemi Engines Made Before the 426 Hemi.
426 Street Hemi Dyno Results
A machine shop located in Massachusetts hooked up a street Hemi rebuilt to factory specifications to a dyno and received the following results:
- 459.3 HP @ 5,000 RPM
- 494.4 HP @ 5,950 RPM
- 498.3 ft. lbs. torque @ 4,500 RPM
At 5,000 RPM, which the factory rated the engine at, this Hemi produced 34.3 more HP than the factory rating.
The engine made it’s peak horsepower, 494.4 at 5,950 RPM. That’s 69.4 more horsepower than the factory rating.
Chrysler, instead of saying the engine had 425 HP @ 5,000 RPM, it’s possible they could have reported 494 HP @ 5,950 RPM instead. But if they did, this wouldn’t be good for insurance or NHRA.
For a complete list of all cars having the 426 Hemi check out my article, What Cars Had the 426 Hemi: Street and Race Hemis.
The engine used in this dyno test was rebuilt to factory specifications except it was bored 0.30 over making it 432 cubic inches.
Because the owner of the engine didn’t want his engine to rev high or maybe break, the dyno test was only performed up to 5,100 RPM. Here are the results:
- 436.8 HP @ 5,000 RPM
- 439.6 HP @ 5,100 RPM
At 5,000 RPM, this engine produced 11.8 more horsepower than what Chrysler rated. See the video directly below showing the exact test.
Just 100 RPM more the horsepower was still increasing and would have kept going up until about 6,000 RPM. Too bad the test wasn’t performed at higher a RPM, it would have been interesting.
Learn more about the carburetors in my article, The Carburetors on a 426 Hemi.
The powerplant in the video below was rebuilt and bored 0.30 over to clean up the cylinder bores.
The block was honed and slightly different compression pistons were used making the compression 10.6:1 instead of the factory compression ration of 10.25:1.
Other than those two things this engine is factory including the following:
- Intake manifold
- The heads were not ported or polished.
- Factory rocker arms and shafts.
- Stock valve job.
- Factory dual point distributor and coil.
The following is how much horsepower and torque the Hemi produced:
- 491.3 HP @ 6,100 RPM
- 493 ft. lbs. of torque at 4,500 RPM.
491 HP instead of 425 HP at a higher RPM, maybe Chrysler should have reported these numbers instead? Here’s the video of the dyno:
The Hemi heads create most of the Hemi power, but what does Hemi really mean? Find out in my article, What Hemi Means in an Engine: Generation 1, 2 and 3 Hemis.
The Hemi tested in this video is factory original and not rebuilt. It’s unknown how many miles were on this engine when it was hooked up to the dyno.
It’s safe to say an engine with some wear and tear shouldn’t produce as much horsepower as new. This is a great test because it’s not rebuilt.
The following is the horsepower and torque numbers:
- 446 HP @ 5,000 RPM
- 452 HP @ 5,500 RPM
- 490 ft. lbs. of torque @ 4,000 RPM
It’s interesting to note the peak torque was produced with the same number and RPM as the factory rating.
The HP at the factory RPM rating was 21 more HP than the factory 425 HP. Don’t forget this number is with a used engine with some wear.
This engine produced a peak HP of 452 at 5,500 RPM. Here’s the video of these results:
There’s more to the horsepower that makes a 426 so special. Find out more in my article, What Makes the 426 Hemi So Special.
The video below has a 426 Hemi rebuilt to factory specifications on the dyno. In the video, not many details are given but it is mentioned the engine produced 496 horsepower at approximately 6,000 RPM.
426 Hemi Engine Real Power Numbers
Above are 5 dyno tests for engines as close to factory specifications as you can find. They have factory cams, heads, valves, carbs and intakes.
Knowing the engine had more horsepower than rated at the factory, let’s answer the question, how much horsepower does a 426 Hemi really have?
The 426 Hemi really has 443.7 horsepower at 5,000 RPM and a peak horsepower of 493.6 at 6,000 RPM.
The 5 tests represent a good indication of the engine’s true power numbers. The following is the average horsepower of all 5 engines:
- 443.7 HP @ 5,000 RPM
- 493.6 HP @ 6,000 RPM
The 443.7 HP average is 18.7 more horsepower than the factory rating of 425 at 5,000 RPM.
Allowing the elephant motor to rev higher like it was designed to do resulted in an average horsepower of 493.6 at 6,000 RPM.
Find out why the Hemi was banned twice in my article, Why the 426 Hemi was Banned From Nascar.
Knowing the powerplant had more horsepower, let’s examine the torque. How much torque does a 426 hemi really have?
The 426 Hemi really has 493.6 ft. lbs. at 4,333 RPM.
The following is the average torque of all 5 engines:
493.6 ft. lbs. @ 4,333 RPM
It’s interesting to note the torque numbers reported by Chrysler is very similar to the torque numbers reported by the engines in the dyno tests.
The 493.6 ft. lbs of torque average is 3.6 more than the factory rating of 490 at 4,000 RPM.
The horsepower numbers showed a huge difference and not the torque. The is probably because peak torque of most engines is at a lower RPM than horsepower.
Also, convenient for the car manufacturers, it was the horsepower ratings affecting the NHRA classes and insurance premiums and not the torque numbers.
Let’s settle the score about which one is faster in my article, The 426 Hemi vs The 440 Six pack: Which is Faster?
Check Out More 426 Hemi Articles!
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- Google books: How to Rebuild and Modify Chrysler 426 Hemi Engines
- Google books: The Definitive Plymouth Barracuda and Dodge Challenger Guide: 1970-1974
- The Mopar Blog: Mopar.com
- GTS: Galen’s Tag Service
- Hemmings: Hemmings.com