What Makes A HEMI Different From A Max Wedge?

Let’s pretend it’s May 1962 and you’re a diehard Chrysler loyalist who loves drag racing. You could search for a used 392 Hemi, but good luck keeping the bottom end from grenading after slapping on an 8-71 blower and running nitromethane. Unfortunately, the 417 Donovan block with its 72-stud main bearing girdle is nine years away from debuting, so that’s not going to help. However, you could plunk down a stack of cash on a new “Maximum Performance” wedge-headed 413-cubic-inch beast, called Max Wedge for short. You heard that Chrysler’s 413 pushed the 300F GT to a top speed of almost 145 mph on Daytona Beach in 1960, and now the engine’s being prepped for quarter-mile runs. 

The 413 Max Wedge was a real monster, making up to 420 hp, more than one horsepower per cubic inch. In 1963, the Max Wedge grew to 426 cubic inches, offering up to 425 street-unfriendly horsepower, but it wasn’t to be the top Mopar offering for long. In 1964, the Hemi came back. Boy, Chrysler just can’t quit the hemispherical combustion chamber. It always weighs the Hemi’s pros and cons, and ends up deciding that the power is worth the downsides. 

In a Hemi, the combustion chambers are, as the name implies, roughly half-spheres, which allows for massive valves, efficient combustion, and excellent airflow. In a Max Wedge, the valves are right next to each other, and run single file in line with the cylinder banks. While this makes for a lighter, cheaper valve train and smaller overall dimensions, it limits the size of the valves and horsepower potential. Still, a 413 Max Wedge-powered Plymouth Savoy nicknamed the Melrose Missile was the first factory stock car to run in the 11s through the quarter.

Before exploring the minutiae of Chrysler’s nomenclature and the specifics of the Max Wedge and Hemi engines in the early ’60s, let’s further examine technical differences. Inspect this picture, noting the variation in piston and valve train design. The top half shows Hemi components, including the splayed-out rocker arms necessary for actuating valves set at dramatic angles. The pushrods come up between the rocker shafts, and both intake and exhaust valves each get their own shaft. Also notice the domed piston, which gives a good idea as to where the valves sit in the head. The bottom half of the picture shows the far simpler wedge-head valve train. Rockers operate on a single rocker shaft and pushrods are more or less parallel. The piston is, for all intents and purposes, flat.

As for branding, in 1962, at Dodge, the engine was called the Ramcharger 413, and at Plymouth, it was the Super Stock 413. Base compression was 11:1 and good for 410 hp, but an optional head-cracking 13.5:1 compression version made 420 hp. While some modern engines need today’s premium gas, a high-compression Max Wedge requires 104-octane Sunoco. Both engines featured the coolest-looking “crossram” intake with dual four-barrel carbs, forged internals, a high-lift cam, and a baffled oil pan. 

In 1963, displacement increased to create the Ramcharger 426 and Super Stock 426. Horsepower bumped up to 415 for 11:1 engines and 425 for 13.5:1 engines. In May 1963, Chrysler made slight improvements and dubbed the engines “Ramcharger 426A” and “426 Super Stock II.” After some further refinement in 1964, the engines became the “426 Super Stock III” and the “Ramcharger 426 III.” These numbers are where the “Stage II” and Stage III” nicknames come from.

Unfortunately for the Max Wedge, 1964 was the year that Chrysler brought back the Hemi. The “Race Hemi” displaced 426 cubic inches and had 12.5:1 compression. It even gained aluminum heads in 1965. Thanks to its success, the “Street Hemi” was born. Though it had a lower compression ratio of 10.25:1, a milder cam, and cast-iron heads only, it still had 425 hp and crushing performance. Meanwhile, the wedge head didn’t die, it just became second banana. Chrysler punched it out to 440 cubic inches and used it in everything from the comfy Chrysler 300 land yacht to the sharp, Mustang/Camaro-battling Dodge Challenger and Plymouth ‘Cuda, where it made up to 390 hp. 

In a horsepower race, manufacturers will do crazy things, and the 1960s saw some stupendous experimentation. Ford’s single-overhead-cam 427 generated more than 600 hp and was sold through speed shops. Chevrolet added fuel injection to Corvettes and produced aluminum blocks for the rare ZL1 427. Pontiac’s Ram Air V heads had intake ports so large that the only place for the pushrods was, well, directly through the port. Oldsmobile even developed a 32-valve 455 that, like an LB7 Duramax Diesel, still used an overhead valve arrangement. Chrysler even tried pushing engine tech forward with a massive prototype double-overhead-cam pentroof 426, which means that Dodge did try to ditch pushrod V8s at one point. 

And American Motors Corp. was, uh, there. Look, the 390 and 401 are awesome engines, but other than the 1957 fuel-injected 327 that never actually made it into the Rambler Rebel, the company’s engines were pretty conventional. If you want crazy AMC, check out a Randall Gremlin 401-XR.