This 870-HP Mustang Outmuscles Ford’s Own GTD And Dark Horse

RTR Vehicles has started handing over keys to its most powerful Mustang yet, and the number on the build sheet is the whole story: 870 horsepower. That figure comes from a supercharged 5.0-liter V8 stuffed into the 2026 Mustang RTR Spec 5, and it puts RTR ahead of Ford‘s own factory halo trims, the Dark Horse SC and the track-focused GTD, in peak output. Deliveries are underway now, with the first of a planned 50 examples already handed to a customer this week.

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That’s the detail that matters for anyone chasing the biggest number in the current Mustang lineup. Ford builds the Dark Horse SC and the GTD as its top performance statements, but neither one is the most powerful Mustang money can buy anymore. RTR, an aftermarket shop founded by drifter Vaughn Gittin Jr., has claimed that title with a car that still carries Ford’s factory warranty.

The Spec Sheet Behind RTR’s Power Claim

Every Spec 5 starts as a standard V8 Mustang before RTR adds the supercharger that pushes output to 870 hp. The company pairs that engine with its Tactical Performance suspension, a 30-way-adjustable setup with coilovers and adjustable front and rear sway bars, letting owners dial in ride height and handling balance for street or track use. Each car rides on 20-inch RTR forged wheels wrapped in Michelin Pilot Sport 4S tires, and a Borla exhaust system developed specifically for the Spec 5 gives it a distinct exhaust note.

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The widebody composite kit is the visual giveaway that separates a Spec 5 from a standard Mustang in the parking lot. Pricing starts at $159,999, and buyers can order through RTR’s North Carolina facility directly or through RTR-authorized dealers. Despite the aftermarket build, every Spec 5 still carries Ford’s 3-year, 36,000-mile factory warranty, which takes some of the risk out of buying a car with this much added power.

Why This Number Matters Against Dark Horse SC And GTD

Ford built the Dark Horse SC and the GTD to sit at the top of the Mustang range, and both carry serious credibility among performance buyers. The Spec 5’s 870 hp figure simply outguns both on paper, which means the biggest-number conversation in the Mustang world no longer ends inside a Ford dealership. For buyers who prioritize peak output above all else, RTR has become the default answer, and it’s doing it while keeping the factory warranty intact, something most aftermarket power upgrades can’t offer.

Customization Comes At A Price

RTR treats the Spec 5 as a build-to-order car, not an off-the-shelf model. Standard paint is included, but premium color options run an extra $7,500, and unique finishes like the Mystichrome shown on early builds push that figure to $15,000, with access to RTR’s paint-to-sample program at that tier. With only 50 units planned and three already built, the window for ordering one is narrow, and RTR’s North Carolina shop is working through customer deliveries now.