Chrysler FirePower Hemi
The infamous Gen II Chrysler Hemi is an engine that needs no introduction. Whether it was in NASCAR, NHRA Top Fuel, or at the local dragstrip, everyone was trying to chase down the big, bad Hemi. Interestingly, Chrysler dabbled with hemispherical combustion chambers 13 years before the 426 Hemi debuted in '64. Launched in 1951, the Gen I Hemi produced 180 hp from its 331 ci of displacement. By 1951 standards, that was pretty darned stout. Consequently, the significance of this engine is rather obvious. Without a Gen I Hemi, there would be no Gen II Hemi.

Not only did Chrysler beat Ford and GM to the OHV punch by several years, Mopar's first OHV engine design boasted trick hemispherical cylinder heads. Building upon expertise it earned while developing aircraft engines during WWII, Chrysler achieved this unique cylinder head architecture by placing the intake and exhaust valves on opposing sides of the combustion chambers. The primary benefits of this setup was that it allowed for a straighter path from the back of the intake port to the manifold, and created extra space for larger valves. Actuating the valves in a Hemi chamber with an in-block camshaft required titling the pushrods at extreme angles, but Chrysler was able to make this arrangement run reliably. The 331 was bored and stroked to 354 ci in 1956, and produced an impressive 355 hp in its top trim level. Chrysler then upped the ante with a raised-deck block in '57, which allowed increasing the stroke even more for a total of 392 ci. The dimensions of this tall-deck block were quite imposing, with a 4.562-inch bore spacing, and a 10.870-inch deck height. The 10.0:1 version of the 392 was rated at 345 hp, and proved very popular with drag racers. A fuel-injected 392 was offered in the Chrysler 300, which churned out 390 hp.

The Gen I Hemi wasn't marketed as a Hemi, and Chrysler dubbed it the FirePower V-8. Chrysler abandoned the Hemi cylinder head architecture in 1958 when production of the Gen I Hemi ended. It was replaced by more traditional and cheaper-to-produce wedge cylinder heads that were introduced along with the new B-series big-block platform that same year. Perhaps recognizing the promise of these hemispherical heads many years later, Chrysler revived the design with the launch of the Gen II 426 Hemi.

That said, the Hemi story doesn't end there. Before the Gen I Hemi was dropped in favor of the B-series wedge motor, Chrysler manufactured a line of "semi-Hemi" V-8s from '55 to '58 called the Spitfire for consumers who didn't want to pony up for the FirePower engine. They used the same 331 and 354ci short-block assemblies as the Gen I Hemi, but were topped with polysphere cylinder heads and a conventional inline valvetrain. The polysphere heads got their name from combustion chambers that resembled two half spheres, and the most potent 354ci variant checked in at 310 hp. Chrysler also produced a 301ci small-bore version of this engine for entry-level vehicles.

"Not only did Chrysler beat Ford and GM to the OHV punch by several years, Mopar's first OHV engine design boasted trick hemispherical cylinder heads."

AMC V-8
The few enthusiasts who know anything worthwhile about the AMC V-8 probably think of it more as a Jeep engine than a genuine hot rod powerplant. That's a reasonable assumption considering that the AMC V-8 was widely used in pre- and post-Chrysler-era Jeeps until the early '90s. Plus, the AMC V-8 is enormously popular amongst off-road Jeep enthusiasts. Nevertheless, AMC's flagship engine has a storied history in the annals of muscle cars, and recently released aftermarket blocks and cylinder heads make it possible to transform one into a seriously wicked hot rod engine.

The first-generation AMC V-8, more commonly known as the Rambler V-8, was built from '56 to '66 for use in Nash, Hudson, and Rambler vehicles. It performed well for its time, with the 327ci variant churning out 288 hp in 1957, however, the thin cylinder walls and limited displacement potential of these engines make them uncommon in both Jeep and hot rodding circles. AMC completely revamped its V-8 for the '66 model year, offering it in 290, 343, and 390ci trim levels. Sized somewhere between a big-block and a small-block, the new Gen II AMC featured a 4.750-inch bore spacing, and a forged crank and rods. Very few parts between the Gen I and II engines interchange. The 390 offered in the '69 AMX was the top dog, generating 340 hp and 430 lb-ft of torque, courtesy of a four-barrel carb and 12.2:1 compression.

For 1970, the AMC V-8 was revised again with the launch of the tall-deck Gen III platform. The basic architecture of the engine remained the same, and improvements included a 5/32-inch raised deck height and revised higher-flowing cylinder heads. Consequently, this allowed for an increase in stroke, and displacement grew to 304, 360, and 401 ci. Power ratings between Gen II and III engines are difficult to compare due to the differences in SAE gross and SAE net rating systems, but as with all engines of the day, horsepower steadily dropped as emission standards tightened up.

Most hopped-up AMC V-8s are based on the Gen III block for its generous displacement potential. With a maximum recommended bore diameter of 4.195 inches and a 9.218-inch deck height, building a 450-plus cubic-inch engine is no sweat. Indy Cylinder Head offers both an aftermarket tall-deck block and cylinder head castings, which pushes the AMC platform to big-block Chevy territory. In fact, Indy sells turnkey 512ci crate AMC V-8s that make 840 hp on motor. How's that for a Jeep engine?