426 HEMI Vs 426 Max Wedge: Are They The Same Engine?

Chrysler experimented with unorthodox combustion chamber designs near the end of World War II, when the company developed prototypes of high-displacement engines with hemispherical combustion chambers for tanks and military aircraft. While the "hemi" showed promise in those applications, the experimental engines were shelved as the war came to a close. In 1951, Chrysler revisited the engine design, using the experience that they gained in the war years to adapt hemi technology for use in production cars. The first generation "FirePower Hemi" continued to power some of Chrysler's most powerful models until 1958, when the Hemi was phased out in favor of a new V8 engine series.

The new V8 engine architecture was introduced in 1958 and featured a more typical combustion chamber design. The new Chrysler B engines featured wedge-shaped combustion chambers, earning them the nickname of "wedge engines." The following year, Chrysler introduced a raised-deck version of the B family called the RB family and began building a 413-cubic inch race version of the RB in 1962, called the Mopar "Max Wedge." With the increase of NHRA and NASCAR engine displacement regulations to 7.0 liters in 1963, the 413 Max Wedge grew to 426 cubic inches, creating the 426 Max Wedge.

The same year as the 426 Max Wedge's introduction, Chrysler president Lynn Townsend ordered the engineering team to get started on another high-displacement V8 explicitly built to destroy Chrysler's competition in NASCAR and on the drag strip. The team went to work, adapting the existing RB block to accept a hemispherical combustion chamber cylinder head, leading to the creation of a new generation of the wildly successful 426 HEMI the following year. While using an adapted Max Wedge block and having the same displacement, the 426 HEMI was a completely different engine than the 426 Max Wedge.

While the 426 HEMI was initially based on the RB architecture used by the 426 Max Wedge, the two engines share very little in common. Both engines have 426 cubic inches of displacement and have the same 3.75-inch stroke and 4.25-inch bore, but that is where the main similarities of the engines end. The biggest differences between the 426 HEMI and 426 Max Wedge can be found in their cylinder head designs, which also meant that the Max Wedge's RB cylinder block had to be heavily modified to accept the HEMI cylinder head.

Wedge-shaped combustion chambers were chosen for the B and RB engine families' cylinder heads due to the fact that they were much simpler and cheaper to build than the hemispherical combustion chamber heads used on the earlier FirePower HEMI V8s. Eventually, the wedge design caught up and smashed the original HEMI's performance with the introduction of the Max Wedge, which featured more aggressive cams, larger ports and valves, a bulletproof rotating assembly, and a sky-high 13.5:1 compression ratio. While the Max Wedge's cylinder heads were competitive, there are a couple of reasons why Mopar reverted back to hemispherical heads for the 426 HEMI.

The 426 Max Wedge's main downfall was cylinder head flow. The wedge's cylinder head was offset from the cylinder bores which shrouded the valves and led to poor flow. In contrast, hemispherical cylinder heads allowed for even larger valves that opened away from the cylinder walls, which improved flow dramatically. The hemispherical shape of the HEMI's combustion chamber also allows cylinder pressure to build up faster in the combustion cycle making its power stroke more efficient.

[Featured image by Trekphiler via Wikimedia Commons | Cropped and scaled | CC BY 3.0]

Both the 426 Max Wedge and 426 HEMI enjoyed success in racing, but the HEMI was the truly dominant engine in both NASCAR and drag racing. The 426 Max Wedge was initially born for drag racing in 1963 when the National Hot Rod Association raised the Super Stock drag racing engine displacement limit to 7.0 liters, or 427 cubic inches.

The 426 Max Wedge came in both a low-compression variant and a high-compression variant with 11.0:1 and 13.5:1 compression, respectively. The low-compression version made 415 horsepower, and the high-compression version made 425 horsepower, taking advantage of a more aggressive cam and better-flowing exhaust system. While 426 Max Wedge Mopars went undefeated in the 1963 drag racing series, they didn't achieve much NASCAR success.

When the 426 HEMI was introduced in mid-1964, it was made in two different configurations for racing only. The first was a track version built for NASCAR, which featured a single Holley four-barrel carburetor. The second was a race version built for drag racing and used twin Carter AFB carburetors on a cross-ram intake manifold. The Track HEMI was rated at 425 horsepower while the Race HEMI was factory rated at 415 horsepower, although those numbers were likely much higher in actuality.

In its first race, the 426 Track HEMI powered the Mopar to a 1-2-3-4 at the 1964 Daytona 500, and the Race HEMI did serious damage in Super Stock as well. The Race HEMI eventually led to the Street HEMI in 1966, which was a detuned version of the legendary 426 that was used in road vehicles.