Chrysler 426 Hemi Engine Guide: Specs, Features, & More

Hemi. The word means different things to different people. There is the new generation of gear heads that think of the spectacular engines from the 3rd-gen Challengers and their crazy horsepower numbers. Then you have the old-school Hemi lovers that remember the 7.0 Liter big-block engine from the muscle car era. Though one-in-the-same, they are VERY different animals.

Focusing on the 426 Hemi, the engine did NOT start under the hood of the famed Barracuda that brings 6-figure price tags nowadays. This engine design started inside a plane. Yup, a World War II fighter.


P-47 Thunderbolt

Chrysler engineers worked with Pratt & Whitney to make engines for the P-47 Thunderbolt and eventually the Patton tank. This gave Chrysler the idea to put this special combustion principle toward their production cars. In the early 1950s, the engine saw its first use in Chrysler and Imperial cars. These first-gen engines were the start of something special – something that would catapult the Chrysler corp to stardom through the muscle car era.

So, what exactly is the Hemi? Well to put it in layman’s terms, it is an engine that has a hemispherical cylinder head – thus a hemi-head design. The design came from the problem of flat pistons creating too little compression – necessitating the “domed” shape.

Second Generation

1964 Dodge Cross-Ram high-rise intake
Photo Source: Hot Rod

The second-gen Hemi, the 426ci behemoth most of us have heard of, was issued in 1964. These engines were sold to just 11,000 customers and were used mostly for drag racing – which was big at the time. However, that didn’t stop some consumers from squeezing this engine into a few aluminum-fendered Mopars – and in the process – scaring their neighbors into submission.

The first production models with the Hemi in them came in 1966 – with cars like the Charger and Belvedere GTX  receiving the race-bred engine for cross-town driving. These cars were not comfortable driving cars and had far more power than anyone should have back then. Tires were garbage, suspensions were just being perfected, safety options were limited, and accident technology was in its infancy.

Unending, Underrated Power

1970 Dodge Challenger 426 Hemi
Photo Source: Hot Rod

The 426 Hemi, referred to as the “street” Hemi in cars from 1966 onward, started with the same power as the engine would carry for its 6-year lifetime – 425 horsepower. The engine was underrated and most likely produced in the neighborhood of 485 or so horsepower – right from the factory.

After opening the hood, you’d notice the Hemi would have one of the widest looks of any production engine. It was not only the biggest looking, but it was also the biggest cubic inch engine in racing at the time of launch. And the sound… mind-numbing. The thump of one of these engines – even with stock exhaust – is enough to produce chills. Low-restrict pipes? It’ll shake you apart.

Beyond the horsepower numbers, the monstrous 7-liter engine put out almost 500lb-ft of torque. To put that into perspective, a 2020 Scat Pack Challenger only produces 475. With the 727 automatic or 4-speed manual gearbox, Mopars would turn into virtual rocket ships with the Hemi under the bonnet.

Performance Examples

Hemi Tested ¼ Mile Time @ Speed
1967 Dodge Charger 14.2 @ 96 mph (Car Life)
1967 Plymouth GTX 13.5 @ 105 mph (Muscle Car Chronicle)
1968 Plymouth Roadrunner 13.5 @ 105 mph (Car & Driver)
1969 Dodge Charger 500 13.4 @ 109 mph (Hot Rod)
1970 Dodge Challenger R/T 14.1 @ 103 mph (Car & Driver)
1970 Plymouth Hemi Cuda 13.1 @ 107 mph (Car Craft)
1970 Plymouth Roadrunner 13.3 @ 108 mph (Super Stock)
1971 Dodge Charger Super Bee 13.7 @ 104 mph (Motor Trend)

As you can see, these mid-size, 4-5 passenger, 3800lb cars would run the quarter-mile in the mid-to-high 13-second range. Ok, so there are luxury Audis and BMWs that will run low-12s nowadays without breaking a sweat. So, why are the figures impressive?

Well, for starters, these beasts had 3-speed auto or 4-speed manual transmissions. Not exceptional for acceleration runs. Next, they didn’t have paddle shifters or electronic gear shifts, so even the automatics would take tenths of time to shift. Then you move on to the horrible, narrow, bias tires of the time. Lousy for anything but burnouts and grocery-getting.

When all is said and done, these cars would be legit 12-second cars with a set of modern tread and low 12-second cars adding a modern transmission.

Simply put, they were fast, loud, and amazing – especially for a time where some seatbelts didn’t have shoulder straps.

1967 Dodge Charger Hemi Engine Specs*

Engine OHV, 90o V8
Bore X Stroke 4.25 x 3.75
Displacement Cu. in. 425.36
Compression Ratio 10.25
BHP 425 @ 5000
Torque 490 @ 4000
Carburation Carter – 2- 4barrels
Valve Operation Mechanical lifters, pushrods, overhead rocker arms
Exhaust System Dual reverse-flow mufflers
Transmission 3-Speed Torqueflite  Automatic
0-60 mph 6.4 sec.
0-100 mph 16.4 sec.
0-¼ mile 14.1 @ 96.1 mph
Top Speed 134 mph
Price as Tested $5,289

* Car Life 2/67

Retired Too Early

With the dreaded gas crunch of the early 70’s, the Hemi was discontinued faster than most big-block engines. The last Hemi was produced in 1971 and it would never be produced again. Yes, the new Challengers boast “Hemi” engines, but these are NOT the same steel monsters of the muscle car era.

Today, you can buy Hemi crate engines and even get them in bigger sizes than the original 7-Liter. They are more sturdy, more powerful, and ridiculously expensive. However, getting an original one in a muscle car would cost you more than 10x as much, so they have become an alternative to the real mccoy. Just scoop up a cheap 318 Charger and you could have your own Hemi-powered Charger R/T for a third of the price.

Either way you slice it, the 426 Hemi was not only one of the most powerful and successful engines of the muscle car era, but are considered the most coveted engine on the market nowadays. Once you’ve driven one, however, you’d never want to be without again.