Although the introduction of the Fox platform for the 1979 model year signified a new, potentially more dynamic chapter for the Mustang, the future of big displacement, naturally aspirated V8s was still uncertain. After debuting with a 302ci, eight-cylinder motor making 140 horsepower as the top dog powerplant, Ford dropped the 5.0 for 1980 in favor a detuned iteration that provided better fuel economy. The new mill displaced 4.2 liters and limped by with an output of 120 horsepower.

Those numbers didn’t offer particularly thrilling performance prospects to enthusiasts. Ford started to test the waters for an alternative in case the V8 wasn’t long for this world, developing a turbocharged version of its 2.3-liter four cylinder engine that would offer similar output to a naturally aspirated V8 while keeping federal regulators at bay.

We absolutely had it to the point where Ford said ‘what a great project’ and we actually did feasibility studies for putting them down the assembly line. — Gary Kohs

At the same time Ford was also keen to re-establish the Mustang as a legitimate contender in the realm of high performance. Gary Kohs, a PR specialist for Ford at the time, concocted the idea of bringing the Mustang back into the fray with a factory road racing effort in the IMSA series, along with a limited production, road-going version of the car the company would campaign.

The M-81’s widebody treatment made it clear that this was a machine built for the race track. Although the mechanicals under the sheet metal of the road-going car were substantially different from the IMSA racer it was based on, the overall look was nearly identical. (Photo Credit: Bring A Trailer)

Gary also wanted to attach the Mustang to a name synonymous with the upper echelons of road racing. To do so, he brought the idea to his friend Roger Bailey at McLaren. The English company had established a U.S. base of operations in Livonia, Michigan back in 1969, putting them in close proximity to Ford’s headquarters, and Roger was on board with Kohs’ idea. This partnership would set in motion the development of the Ford McLaren Mustang M-81, one of the rarest factory-authorized Mustangs of all time.

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Development & Specifications

The hand-built M-81 was a far cry from the garden-variety production Mustang that served as its foundation. Sporting bulging bodywork was created by Dave Kent of Creative Car Craft, it was clear even from a glance that this machine was a departure from the norm. But as with the rest of the modifications, they were as much about elevating the car’s capability as they were about turning heads — the unique hood featured functional heat extractors, the flared steel fenders allowed for wider wheels and tires to bolster the Mustang’s handling, and the unique front fascia curtailed front end lift at high speeds while also helping to keep brake system temperatures down with its integrated cooling ducts.

While the interior of the M-81 shared the same door panels, dash, and center console as the factory production four-cylinder Mustang, there were a number of other changes that made it clear this was no typical pony. The factory steering wheel was replaced by a 14-inch leather-wrapped wheel from Racemark, and behind it, a unique Stewart-Warner instrument panel was integrated into the factory dash to provide real-time information about the engine’s vitals.

After a 10-year hiatus from factory efforts, Ford was ready to mix it up on the world stage of endurance racing once again. They were also eager to prove the new Fox platform was a capable performer, and sought a partnership with a respected outfit to help get the point across to the public. (Photo Credit: Ford Motor Company)

To help keep occupants firmly planted in their seats during high-lateral-G maneuvering, a pair of Recaro LS seats replaced the factory units up front. Air conditioning was optional, as was an SCCA-approved, bolt-in roll bar.

Of course the M-81 package wasn’t just an aesthetic treatment. Underpinning the car was a heavily reworked suspension system that featured adjustable Koni shocks and struts, stiffer springs, and police package sway bars from the Ford Fairmont with tungsten bushings. Stopping power up front was provided by calipers Mustang GT that were paired up with 10.6-inch rotors, while 9-inch drums were installed in the rear, and the M-81 road on three-piece lightweight 15×8-inch BBS wheels that were wrapped in 255mm-wide Firestone HPR rubber.

While the interior design didn't deviate dramatically from the standard Mustang, changes like the smaller steering wheel, Recaro seats, and optional bolt-in cage gave the M-81 a much more purposeful vibe than any other performance-oriented Mustang that Ford had in production at the time. (Photo Credit: Bring A Trailer)

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Underhood Upgrades

But perhaps the most significant element of the M-81 package lurked under the hood. Using factory 2.3-liter blocks, McLaren blueprinted, polished, and de-burred the engines to bolster durability. While the 9.0:1 engine were mechanically similar to the factory turbo four-cylinder mills, McLaren allowed for the powerplant to handle more boost from the Garret T-3 turbocharger. Although 175 horsepower might not sound like much today, it was an increase in output of more than 30 percent versus the standard turbo four-cylinder’s 132 horsepower. A pair of car were also reportedly outfitted with adjustable boost controllers, while a range of 5-11 psi allowed the engine’s output to potentially be ratcheted up to 190 horsepower and beyond.

Although the 2.3-liter, McLaren-tuned engine wasn’t exactly setting the world on fire with 175 horsepower, it helped paved the way for a boosted four-cylinder high performance model to join the Mustang roster later on. It’s also worth noting that this engine produced nearly 50 percent more horsepower than the 4.2-liter V8 that was available in the GT at the time. (Photo Credit: Bring A Trailer)

The M-81’s performance must be evaluated within the context of its time, though. A road test in the December 1980 issue of Motor Trend revealed a 0-60 sprint of 9.76 seconds on the way to a quarter-mile time of 17.37 seconds at 79.20 mph. But these were respectable numbers for the day, and Gary’s project seemed destined to complete its planned production run.

IMSA Racing Effort

A crash early in the race at the M-81’s first IMSA event — the 24 Hours of Daytona endurance race — should have resulted in a Did Not Finish, but the team managed to cobble the car back together and complete the entire race – a feat that received no shortage of publicity in both American and Europe. While both the road-going M-81 and its racing counterpart were motivated by four-cylinder engines, notably hotter hardware was selected for the racing machine. Under the hood was a naturally aspirated 1.6 Cosworth twin-cam BDA motor with Weber carburetion that sent north of 300 horsepower to the rear wheels through a four-speed manual gearbox. Only two were built. (Photo Credit: Ford Motor Company)

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The SVO Effect

While the original plan called for 250 examples of the M-81 Mustang to be built, but only 11 were produced in total, including the original prototype. Several factors stood in the way of the M-81’s success, and chief among them was the car’s $25,000 price tag, a princely sum in 1980 – especially when a standard Mustang GT cost less than a third of that.

Though the MSRP was steep, there was a substantial amount of enthusiasm for the M-81 both within Ford and the public at large. According to an interview published by Hagerty, Gary said, “We absolutely had it to the point where Ford said ‘what a great project’ and we actually did feasibility studies for putting them down the assembly line. There was no problem.”

At more than three times of the price of a GT, it was clear from the outset that the M-81 was never destined for mass production. But even the goal of building 250 examples in total proved to be too much. Just ten would be produced, along with the original prototype. Image: Bring a Trailer

Instead, what would doom the M-81 project was Ford’s own Special Vehicle Operations group, or SVO – a skunkworks department within the company that was just getting up to speed at the time. After seeing the potential for a high-performance iteration of the four-cylinder Mustang that combined V8-level straight-line pull with the road-holding capability of a lightweight, Ford decided to pull the plug on the M-81 project in favor of developing their own take on the idea a few years later – a model which we know today as the Mustang SVO.

While both the M-81 and SVO models would eventually be put out to pasture as Ford’s development of the push rod 5.0 progressed and output far exceeded that of the boosted four-pot, both serve as harbingers of a turbocharged future — one that includes the turbocharged four cylinder-powered Mustang EcoBoost we have today.

Due to the fact that the Ford-McLaren Mustang M-81 is one of the rarest Mustang models ever built, these cars command sums even higher than the original lofty asking price on the second-hand market (when you can find them). Seven examples were painted Bittersweet Orange, one in black, another in white, and the other two received the Enduro GT prototype treatment.

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