By the tail end of the 1960s, the gloves were off in the factory horsepower wars — nearly every major domestic automaker had a massive V8 that made gobs of power available on the options sheets of their performance-focused coupes. For enthusiasts with the means, pavement scorching capability was readily accessible nearly everywhere you looked.

However, alongside this steady climb in horsepower was a trend that saw muscle cars getting bigger and more laden with options and accessories. While this provided more luxurious cruising, it also translated to more weight, a well-known enemy of performance. And whether at the drag strip or out on cruise night, the inherent desire to make one’s ride stand out among a sea of capable performers saw a contingent of buyers looking for something beyond factory-spec, but would offer a bit more refinement than a straight-forward DIY project.

Though the addition of “X” package in 1971 gave the Gremlin some visual appeal, the compact was still lacking the hardware to really attract performance-minded buyers. In its first two years on sale, the Gremlin was only offered with six cylinders under the hood, good for a best-case scenario of 150 horsepower from an optional 4.2-liter mill in 1971. But while the tide was turning away from muscle cars in the early 70s, AMC bucked that trend by offering its 304 cubic-inch V8 in the Gremlin in 1972, which in turn set the stage for a 401ci V8 swap. Image: Hobby DB

This, in turn, resulted in the rise of high-performance dealers across the country. These shops would take delivery of factory machines and inject an additional dose of capability that went beyond what the automaker’s top tier offering could provide.

At a time when General Motors had a corporate rule that made any motor in excess of 400 cubes verboten in anything but a Corvette, Don Yenko came to the rescue with his L-72 427ci-powered Yenko Camaros, Novas, and Chevelles.

When enthusiasts sought an edge over the competition during the original muscle car era, they often turned to high-performance dealerships for both knowledge and parts. Outfits like Yenko Chevrolet and Grand Spaulding Dodge would become recognized commodities for capability they could dial into these already-potent factory machines. Randall AMC of Mesa, Arizona would emerge as one of the premiere performance houses for American Motors machines. Image: Randall Rambler/AMC Jeep Eagle FB Page

Meanwhile, Tasca Ford was finding ways to put big-cube power in the hands of younger buyers who couldn’t afford the expense that came along with the Shelby Mustangs, while Mr. Norm’s Grand Spaulding Dodge would grow to become a performance mecca for Mopar enthusiasts throughout the 60s.

But these high-performance dealers were also among the first casualties of the seismic shift that happened in the industry in the early 1970s, and as factory high-performance offerings began to be killed off, so too were the ultra-high performance models built by these dealers.

Randall AMC dealership in Mesa, Arizona, apparently didn’t get the message though. In 1972, with the endorsement of AMC corporate, the performance dealer would unleash the most potent “factory” Gremlin ever produced — the 401-XR.

The Randall Formula

If the power to weight ratio was becoming an issue with model bloat toward the end of the muscle car era, the Gremlin served as a utilitarian response to the problem. With a 96-inch wheelbase, this diminutive compact weighed in at roughly 2600 pounds depending on its configuration, which made it nearly half a ton lighter than a ’71 Ford Mustang or Dodge Charger.

That certainly provided the Gremlin with a significant weight advantage, but it wasn’t until 1972 that AMC would offer V8 power in the Gremlin. By then federal regulators had already had their way with the automotive industry, and AMC’s top-spec 304ci V8 only made 150 (net) horsepower. While it was enough to keep the Gremlin a lively option at a time when viable performance models were becoming a rare commodity, it fell far short of the true potential of the package in the eyes of Grant and Mike Randall.

Randall AMC was no bandwagoning late-comer to the high-performance dealer game though. Since 1967 the dealership had been hopping up Hornets, Ramblers, and other AMC vehicles. They’d also put together a “how-to” guide for AMC performance, outlining tuning, blueprinting, parts combinations, and other tips for enthusiasts looking to dial more capability into their cars.

A batch of 401 engines awaiting installation in Gremlins that were earmarked for 401-XR conversion at the Randall AMC dealership. Since the external dimensions of the 304ci V8 and 401ci V8 are identical, fitment of the bigger-displacement motor was a straight-forward proposition. AMC’s factory V8 package included the beefier suspension and brakes that a car with this sort of power to weigh ratio would need, so for under $3K, buyers could get that bigger engine in an otherwise unmodified 304 car and run 13-second quarter miles right off the showroom floor. Image: Gremlin X

With AMC taking the SCCA Trans-Am championship in 1970, the company was starting to look like one of the few manufacturers who were still interested in catering to young performance buyers, and Randall AMC would quickly become the go-to shop for the most potent American Motors hardware.

Once AMC had developed components to get the Gremlin to accept the 304ci V8 for the 1972 model year, a swap to the larger-displacement, 255 horsepower 401ci V8 was almost inevitable. The two motors’ external dimensions are identical and thus required no special fabrication to make the 6.6-liter power plant work with the factory motor mounts and crossmember, while the heavy-duty suspension and larger brakes equipped to the 304 V8-powered Gremlins made the transplant largely hassle-free for the dealership.

For a mere $2995 a buyer could leave the Randall dealership with a Gremlin 401-XR which was essentially factory stock aside from the engine swap and good for high 13-second quarter mile times right out of the box.

In spring of 1972, Car Craft put a well-optioned Gremlin 401-XR through its paces. Outfitted with the optional ignition, exhaust, and camshaft upgrades, the magazine posted a quarter mile run of under 12.3 seconds — more than a second and a half quicker than a “base” Gremlin 401-XR. Image: Gremlin X

However, those willing to spend a bit more could choose from a healthy list of options that included headers, a four-speed manual transmission, a Twin Grip rear end, a high rise intake manifold and other go-fast goodies.

As illustrated by Car Craft in May 1972, a well-optioned 401-XR could post much better quarter mile times than the base car, as their best run of 12.22 attests.

Legacy

While the capability of the Gremlin 401-XR was undeniable and the value proposition to enthusiasts looking to go fast in 1972 was seemingly alluring, AMC’s reputation as an economy car builder who had touted at the debut of the 1964 Rambler Typhoon that “the only race we care about is human race” proved difficult to shrug off in the eyes of the performance-minded buyer. Among the nearly 360,000 AMC Gremlins produced between ’72 and 1974, just 21 examples of the 401-XR would be built in total.

Due to their scarcity as well as the difficulty in proving authenticity, coming across an original 401-XR is difficult today. On the rare occasions that they do become available the asking prices have been fairly lofty, which may see these cars becoming collector curiosities rather than show-going drivers as the years roll on.

However, cloning a 401-XR is essentially the same process for intrepid DIYers today that it was for Randall AMC back in the early 1970s, so getting 401ci power into the engine bay of a Gremlin remains a fairly straightforward proposition — provided you can find the parts needed to do the swap. As a result, well-sorted tribute cars have proven to be much more accessibly priced.