1970 Ford Mustang Boss 520 review muscle classic car

1970 Ford Mustang Boss 520 review muscle classic car

In fact, we’ll be the first folks to drool over a really nice custom that shows the creativity of a dedicated enthusiast. But, we also have the ability to offer you professionally built ‘one of one’ muscle cars that were designed and assembled by some of the best names in the hobby, officially named the Boss 520. From its fresh white paint to its unique Intro wheels, this Ford is the stuff dreams are made of.

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1970 Ford Mustang Boss 520 review muscle classic car

If you’re looking for the ULTIMATE pro-tourer to spend time riding in, instead of time working on, it’s an excellent place to park your money


It seems all re-imagined classics have a story, and the Boss 520 is no exception. Back in 1969 Ford was doing exceedingly well in NASCAR, but getting absolutely whipped on the Trans Am circuit. As a result, legendary car exec Bunkie Knudson decided to commission a Mustang that utilized the brand’s NASCAR technology to enhance its SCCA performance. Unfortunately, Henry Ford II showed Bunkie the door before that model could get built. And Kar Kraft Engineering, manufacturers of the firm’s mighty Boss 429, only produced two prototypes of the would-be 1971 Mustang Boss. Those prototypes, officially named the Composite Mustangs and unofficially nicknamed the Quarter Horses, started with Ford’s Boss 429 chassis, added a ’69 fastback body, bolted up a ’69 Shelby GT500 nosepiece and threw in a Cougar dash for good measure. Both of Ford’s storied Quarter Horses survive today. And 40 years after they originally broke cover, someone decided it would be an excellent idea to produce a no excuses replica.


The project started when Kaucher Kustoms sent a design study to Coraopolis, Pennsylvania’s RPM Hot Rods. Naturally, the experts at RPM decided that an idea this cool was worthy of more than just some glorified driver. So, they executed a ground-up build that ensured the newly christened pony would perform every bit as good as it looked. That meant sourcing a roster of top notch components and fresh Dynacorn metal. Once that metal was smooth, many labor-intensive modifications, including a filled and re-imagined hood, filled and relocated side scoops and a custom rear valence, were painstakingly perfected. And today, thanks to our own RKM Performance Center, that massaged fuselage reflects spotless white paint under a traditional black hood treatment and bold “BOSS 520” callouts.

1970 Ford Mustang Boss 520 review muscle classic car

Despite its obvious 21st century appeal, the car you see here is actually very similar to the Quarter Horses that inspired it.

At the front of its body, a fiberglass Shelby GT500 valance hangs a tweaked grille between modern halogen headlights, a flush-fit bumper and smoked marker lamps. At the top of that grille, a custom-fabricated hood bridges the gap between Ringbrothers pins, Detroit Speed wipers and like-new glass that’s framed in body-matched trim. At the edges of that hood, a clean profile hosts body-matched mirrors, Ringbrothers door handles and relocated side scoops. And at the back of the car, smoked Shelby taillights reflect custom, center-mount exhaust tips.


A couple years back a few of us fielded a killer project by the name of RK527 in the 2014 Hot Rod Power Tour. Well, as you might remember from our pre-tour teasers, Jon Kaase was nice enough to make the trip to Charlotte to provide a custom tune. We figured, since he’d be at the RKM Performance Center anyway, we’d go ahead and ask him to take a look at this Ford’s Kaase 520. And while we haven’t put the car on a dyno since that visit, we do know the mill put down 770 dyno-proven horsepower and a whopping 720lb./ft. of pavement-melting torque when originally installed. Pull the pins and you’ll find 520 cubic inches of Boss Nine V8 that’s been tweaked, bathed in a slick coat of black paint and fully dressed in some of the best aftermarket components on the planet. Up top, a custom air cleaner feeds a coated Quick Fuel carburetor through what appears to be a re-usable filter element. Below that carb, a powder-coated Jon Kaase intake is bolted between aluminum Kaase Boss 9 heads that are finished with powder coated “BOSS 520” valve covers and polished aluminum breathers. Below those heads, a Comp hydraulic roller cam creates explosive combustion with the help of an MSD Pro-Billet distributor and MSD 6AL ignition. At the sides of that cam, custom Stainless Works headers send vaporized dinosaurs into a brutal sounding, true-dual exhaust system. And in front of those headers, Billet Specialties Tru Trac components spin an Edelbrock water pump between a chrome alternator, a chrome AC compressor and a Billet Specialties power steering pump. Cooling for the massive powerplant is provided by a Performance Rod & Customs radiator, which is complete with molded water tubes, a custom support topper and two electric puller fans. Fuel is provided by quality braided hoses that are threaded to a chrome Holley regulator and small Earl’s pressure gauge. The vicious sounding engine rides in an OEM-quality bay that wears traditional satin paint under custom-finished shock towers, cool Ringbrothers hinges and a custom hood prop.

1970 Ford Mustang Boss 520 review muscle classic car

The enlightened Ford enthusiast will immediately spot a recessed firewall that significantly aids the car’s tenacious performance.


The bottom of this awesome Mustang is just as impressive. Behind the massaged motor you’ll find a Tremec T56 Magnum 6-speed that’s engaged through a tough Centerforce clutch. Lift the third pedal and that modern transmission sends power to a slick Currie 9-inch, which spins a stout Detroit Locker posi around big, 3.89 gears and beefy, 35-spline axles. Stopping is a cinch thanks to power-assisted Baer discs, which utilize four 6-piston calipers to clamp four 14-inch drilled and slotted rotors. At the front of the car, tubular control arms and Total Control Products spindles frame a thick sway bar, Ridetech coil-overs and Total Control Products power rack-and-pinion steering. At the back of the car, a modified Ridetech 4-bar utilizes custom tubs and a second set of Ridetech coil-overs to provide excellent grip. Between those suspensions, sturdy Total Control Products subframe connectors perfectly complement a heavily modified floorpan that’s been sealed in thick Herculiner undercoating. At the back of those floors, a custom fuel tank feeds braided lines and a spry Holley pump. Spent gases traverse custom, ceramic-coated pipes, which crawl through brutal Flowmaster mufflers. Power meets the pavement through custom Intro wheels, which spin 245/40ZR18 and 335/30ZR18 BF Goodrich G-Force T/As inside slightly stretched wheel openings. And every detail under this slick Mustang, from its Tuff Stuff starter to its deep Moroso oil pan, has been carefully planned and professionally executed.


Open this pony’s solid-fitting doors and you’ll find a tasteful custom interior that was likely the most labor-intensive part of the car’s entire build. Racing-inspired seats mix striking red stitching with serious Ridetech harnesses. In front of those seats, a custom, red-detailed dash hangs clean telemetry between small tweeters, Vintage Air climate control and custom-framed Clarion infotainment. Beneath that dash, a leather-covered, red-stitched console props an MP3 jack behind a short, red-topped shifter and requisite power window switches. Beneath that console, fade-free carpet bridges the gap between custom-machined foot pedals, RPM sill plates and a tough Ridetech TigerCage. At the sides of that carpet, traditional door panels hang sculpted armrests under polished stainless inserts. In front of the driver, a sporty Sparco steering wheel laps a tilting Flaming River column. And behind the passengers, a custom-fabricated cargo hold anchors two Kicker subwoofers between two Kicker QS quarter speakers and 1,500 watts of Kicker IX amplification.

Absolutely no expense was spared on this killer Mustang pro-tourer. Clean, attractive and ready to roll, it combines professional grade performance hardware with some of the coolest customization in the hobby to create a take-no-prisoners muscle car.