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5 Forgotten Domestic Engines That Went Against The Detroit Grain

Detroit is famous for building powerful V8s, strong diesels, and even ultra-reliable straight-six engines — but what about the motors that rarely ever get mentioned? It turns out that peeling back the history of domestic automakers reveals a long list of intriguing engine designs that were unique and innovative in their time, but which, for various reasons, never caught on with the automotive mainstream.

Pontiac Firebird Sprint front view

Which of these unusual power plants do we think deserve the most attention? Here's a look at 5 forgotten domestic engines that went against the Detroit grain.

5. General Motors Twin-Six V12

Did you think Cadillac was the recipient of that last 12-cylinder engine GM ever made? Think again, because in the 1960s the automaker took a break from building V8 muscle cars to create one of the largest V12 engines ever produced.

GMC TwinSix V12 illustration

Part of the reason that GM's most recent V12 dwells in obscurity is because it was never intended for the passenger car market. Instead, the motor was aimed specifically at commercial truck operators who needed more torque than what the traditional 427 cubic inch big block could give them.

GMC TwinSix V12

The V12 displaced a whopping 702 cubic inches, and while it was similar in design to the General's 350 cubic inch industrial V6, it also featured a one-piece block, seven main bearings, and four gallons of oil capacity. The crankshaft alone weighed nearly 200 lbs. Torque for the monster checked in a 625 lb-ft at 2,100 rpm, which rivals turbodiesels in terms of low-end performance, while horsepower was a more modest 275 ponies. Although the engine left the GM catalog in 1965 after five years of production, there's a surprisingly healthy market for these engines today, with rebuilt units readily available. 

4. Chevrolet / GMC Inline-Five

A more modern motor that's been buried in the popular consciousness was the 3.5L (later 3.7L ) inline five-cylinder that found its way under the hood of a host of Chevrolet and GMC products in the early 2000s.

Hummer H3 I5

The Atlas family of engines were branded as Vortec 3500 and Vortec 3700, and sprinkled throughout the mid-size truck and SUV line-up. The five-cylinder version was derived from the more common inline-six that motivated a diverse range of GM-badged crossovers and sport-utilities at the time, and is notable for being the only five-banger ever designed and sold by a Detroit manufacturer.

Hummer H3

Capable of between 220 and 242hp (and with a maximum torque rating of 242 lb-ft, making the 3.7L version a 'square' motor), the I5 was primarily deployed in the Chevrolet Colorado and the GMC Canyon (along with Isuzu's i-Series branding of the same trucks). Hummer H3 buyers were also able to select the five-cylinder engine at ordering time, and it lasted in one form or another from 2004 to 2012.

3. Buick 215 Turbo V8

Everyone knows about Buick's famous 3.8L turbo V6 that made its name in the '80s with the Regal T-Type, Grand National, and GNX. Fewer people are familiar with the first turbocharged Buick motor, however, which debuted nearly two decades beforehand.

Buick 215 Turbo V8

Buick's 215 cubic inch V8 was the automaker's first all-aluminum motor, making it an outlier when it arrived in 1961 for use in smaller cars offered by General Motors. By 1962, it had become embroiled in GM's experiments with forced induction when it was made the beating heart of the Oldsmobile Jetfire, which was the first turbocharged mass-produced vehicle in history.

Oldsmobile Jetfire

With a rating of 215hp and 300 lb-ft of torque, the Buick-cum-Oldsmobile motor impressed with its performance. Unfortunately, the carbureted setup arrived well before the dawn of computer-controlled ignition systems, which meant the high compression motor had no way of dealing with knock. Throw in owners not accustomed to the delicate care and feeding required of an early turbocharged engine, and Oldsmobile was forced to withdraw the Jetfire from the market the following year.

2. Chevrolet LT5

Although the Chevrolet Corvette is perhaps the world's most famous pushrod performance car, there was a time when the path forward for the coupe seemed to be pointing in a very different direction. Specifically, the 1990-1995 ZR-1 introduced the 32-valve, dual-overhead cam LT5 V8 to the Corvette faithful, setting horsepower records for the model in the process.

Chevrolet LT5 V8

Designed in conjunction with Lotus, the aluminum engine was loosely based on the more common 5.7L L98 eight-cylinder, with a dramatically reworked head, intake runners (16 in total), and bore centers. Built by Mercury Marine in both Gen I (375hp) and Gen II (405hp) versions, it was a monster motor that proved Chevrolet could stand toe-to-toe with the best in the world when it came to sports car performance during the heat of the early '90s.

Chevrolet Corvette ZR-1

General Motors eventually decided against developing the 32-valve design any further, instead throwing its engineering weight behind another titan of small block performance, the LS family of engines that would appear in the 1997 Chevrolet Corvette. Slowing sales of the C4 generation 'Vette, which had been left on the market long past its best-before date, would be the final nail in the LT5's coffin, especially considering the ZR-1's enormous $34,00 price premium over a base Corvette.

1. Pontiac Cammer Straight Six

Not every high performance engine offered by Pontiac in the heat of the muscle car era was a V8. John DeLorean was an innovator at nearly every level during his time with General Motors, which is how the Pontiac 'Cammer' inline six came into being as an unusually advanced option for the brand's entry-level autos in the mid-60s.

Pontiac Cammer I6

The Cammer stood apart thanks to its overhead camshaft design, non-interference cylinder head, rubber timing belt (instead of a less smooth chain), and a relatively high redline. In standard form, the 230 cubic inch engine was good for 165hp and it served as the base motor for a number of Pontiacs such as the Tempest and the Pontiac Firebird.

Pontiac Firebird Sprint Convertible

Spend a little more money and you could get the 'Sprint' package for both, which delivered a higher compression ratio, a four-barrel carburetor, and a more aggressive camshaft. The sum total of the upgrades elevated the Firebird Sprint and Tempest Spring to 215hp and 240 lb-ft of torque until the Cammer stopped production after 1969.

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