426 Hemi Engine: What a Hemi Is, Gen II vs Gen III, and 426 Gen III Crate Engines
A Hemi is an engine whose combustion chambers are shaped like a half-sphere (“hemispherical”), with the intake and exhaust valves set at an angle on opposite sides of the chamber. Chrysler’s 426 Hemi of the 1960s, a 426 cubic inch (7.0L) V8 rated at 425 HP in street form, made the name famous. Today “426 Hemi” also describes new crate engines built on Chrysler’s modern Gen III Hemi design, such as BluePrint’s 610 HP 426.
What does Hemi mean?
“Hemi” is short for hemispherical, the dome shape of the combustion chamber in the cylinder head. Because the valves sit on opposite sides of the dome instead of in a row, there is room for large valves and a fairly direct path for air into and out of the cylinder, with the spark plug near the center of the chamber. The trade-offs are wider, heavier cylinder heads and a more complex valvetrain than a conventional wedge-chamber engine.
Hemi vs non-Hemi (wedge) engines
| Hemi chamber | Wedge chamber | |
|---|---|---|
| Chamber shape | Dome (half-sphere) | Wedge, with the valves in a line |
| Valve layout | Intake and exhaust on opposite sides, angled | Side by side |
| Strength | Large valves and good airflow at high rpm | Compact, lighter heads, simpler valvetrain |
| Examples | 426 Hemi, Gen III 5.7L, 6.4L (392) | Most small block and big block V8s |
The original 426 Hemi
| Specification | 426 Hemi (1960s) |
|---|---|
| Displacement | 426 cubic inches (7.0L) |
| Bore x stroke | 4.250″ x 3.750″ |
| Introduced | 1964 for racing; Street Hemi from 1966 |
| Street Hemi rating | 425 HP and 490 lb-ft (gross) |
| Chambers | True hemispherical, one spark plug per cylinder |
The 426 was Chrysler’s second-generation Hemi. It was built for NASCAR and drag racing first, then offered in street cars from 1966 to 1971. Original engines are now collector items, and the 426 name lives on in new Hemi crate engines.
Hemi generations: Gen I, Gen II and Gen III
- Gen I (1951 to 1958): Chrysler’s first Hemi V8s, in sizes up to 392 cubic inches.
- Gen II (1964 to 1971): the 426 Hemi described above.
- Gen III (2003 on): the modern Hemi, introduced as a 5.7L and later built as the 6.1L, the 6.4L (392 cubic inches) and the supercharged 6.2L used in Dodge Hellcat models.
Gen II vs Gen III Hemi
The Gen III Hemi shares the name and the angled-valve idea, but it is a different engine from the 1960s 426, and parts do not interchange. Its combustion chambers are shallower than the classic Hemi’s, and it fires two spark plugs per cylinder. Many Gen III engines also use variable valve timing (VVT) and cylinder deactivation (MDS), and they are controlled by an engine computer. Factory Gen III sizes are 5.7L (345 cubic inches), 6.1L (370), 6.4L (392) and the supercharged 6.2L, which was rated at 707 HP when the Hellcat arrived for 2015.
A modern “426” is a Gen III Hemi built to 426 cubic inches, so it combines classic displacement with the modern design and fuel injection.
BluePrint 426 Gen III Hemi crate engines
BluePrint’s 426 Gen III Hemi crate engines are designed as retrofits for early Dodge and Plymouth muscle cars and Dodge pickups. According to the product listings, each one has:
- A cast-iron Hellcat/Apache-type block with 4-bolt mains, a forged steel crankshaft (4.05″ stroke) and forged pistons
- Apache aluminum cylinder heads with 73cc chambers and 10.48:1 compression
- A hydraulic roller camshaft, with VVT locked out and MDS eliminated
- A muscle-car style mid-sump oil pan, a fabricated intake manifold and a throttle body
- A Holley Terminator ECU controller kit with wiring harness, and a 58X reluctor wheel
| Engine | Part number | Version | Rating | Price |
|---|---|---|---|---|
| BluePrint 426 Gen III Hemi EFI | PS426CTF | Base dressed | 610 HP, 525 lb-ft | $16,899.00 |
| BluePrint 426 Gen III Hemi EFI, drop-in ready | PS426CTFKB | Deluxe dressed with black front accessory drive | 610 HP, 525 lb-ft | $18,899.00 |
| BluePrint 426 Gen III Hemi EFI, supercharged | PS426SCTK | Drop-in ready with polished accessory drive and Whipple 3.0L supercharger | 872 HP, 764 lb-ft | $26,799.00 |
The accessory-drive versions include the water pump, alternator, power steering pump and A/C compressor. Prices change, so check the product page for the current price. Every order ships for a flat $75 to any US state. See all Mopar crate engines.
Putting a 426 Gen III Hemi in an older car
- Fuel system: an EFI engine needs a high-pressure electric fuel pump, a return or returnless regulator setup and suitable lines.
- Mounts and transmission: plan the engine mounts, the transmission and its flexplate or flywheel for the Gen III engine, since swap parts made for classic Mopar engines do not always fit.
- Exhaust and clearance: the wide heads need headers that clear your chassis and steering.
- Engine control: the BluePrint engines include the Holley Terminator ECU kit, so wiring is simpler than with a factory computer.
Read our guides to crate engines and carburetor vs fuel injection.
Frequently asked questions
What is a Hemi engine?
An engine with hemispherical (dome-shaped) combustion chambers and valves angled on opposite sides of the chamber. Chrysler’s Hemi V8s, including the 426 and the modern 5.7L and 6.4L, are the best-known examples.
How much horsepower does a 426 Hemi have?
The 1960s 426 Street Hemi was rated at 425 HP (gross). BluePrint’s modern 426 Gen III Hemi EFI crate engines are rated at 610 HP and 525 lb-ft.
What is the difference between a Gen II and a Gen III Hemi?
The Gen II is the 1964 to 1971 426 Hemi with true hemispherical chambers and one spark plug per cylinder. The Gen III, from 2003, is a different design with shallower chambers, two spark plugs per cylinder and electronic fuel injection.
Is a 426 Gen III Hemi the same as a 392?
No. The 392 is Chrysler’s factory 6.4L Gen III Hemi. A 426 Gen III Hemi is built to a larger 426 cubic inches; BluePrint’s uses a 4.05″ stroke forged crankshaft.
Do the BluePrint 426 Hemi crate engines include an ECU?
Yes. The listings include a Holley Terminator ECU controller kit with a wiring harness.
What cars came with the 426 Hemi?
From 1966 to 1971 the Street Hemi was an option in Dodge and Plymouth muscle cars, including the Dodge Charger, Coronet, Super Bee and Challenger and the Plymouth Belvedere, Satellite, GTX, Road Runner and ‘Cuda. Original Hemi cars are now collector items; the BluePrint 426 Gen III Hemi crate engines we list are new engines designed as retrofits for early Dodge and Plymouth muscle cars.
Is there a supercharged 426 Hemi crate engine?
Yes. The BluePrint PS426SCTK is a 426 cubic inch Gen III Hemi crate engine with EFI and a Whipple 3.0L supercharger, rated at 872 HP and 764 lb-ft. It is a modern Gen III design, not a supercharged version of the 1960s 426 Hemi.
Related: 426 Hemi crate engines, what is a crate engine?, long block vs short block, crate engine prices, engine management, all guides.
Comments