A rare V10 prototype of the Ford Mustang known as the Boss 351 has been restored and run on a dynamometer after spending a quarter-century out of the public eye, according to reporting by Hot Rod and documentation from Ford. Built around the turn of the millennium, the one-off vehicle features a custom 5.8-liter 10-cylinder engine that delivers 510 horsepower to the wheels without forced induction.
Development History of the Boss 351 V10 Prototype
During the production of the facelifted fourth-generation Mustang, a team of six Ford employees worked outside official funding channels to build a large-displacement alternative to the standard V8 engines. According to statements given by Kevin Byrd to Hot Rod, the project was led by Grega Coleman, Jima O’Neill, Paula Velly, Dona Masche, Mika Shelby, and John Bruno. The group received assistance from the engine research plant division, crafting a powerplant intended to pitch Ford into the supercar segment against the Dodge Viper and Chevrolet Corvette.
Engineers bypassed Ford’s existing 6.8-liter Triton V10 used in large pickup trucks. According to project records, the truck engine was too large and tall for the Mustang engine bay and utilized split crankpins typical of V6 designs. Instead, the team took a 4.6-liter Modular V8 engine from the Ford family and extended it by two cylinders, creating a 5,752 cubic centimeter block that retained a 90-degree bank angle. Heads and camshafts were derived from the Cobra R specification and lengthened to fit the new layout.
Engine Specifications and Dyno Performance
The resulting Boss 351 engine operated without split crankpins, running opposite connecting rods on a shared journal just like a V8. This configuration produced a distinct firing order alternating between 90 and 54 degrees of crankshaft rotation. According to Ford performance figures, the powerplant utilized pistons from the Cobra R alongside a 10:1 compression ratio.
When measured on a dynamometer during its recent restoration, the naturally aspirated V10 produced 510 horsepower at the wheels. For comparison, the top-tier production Mustang of that era, the Cobra R equipped with a 5.4-liter V8, officially rated its engine at 390 horsepower, which translated to roughly similar figures on the wheels during testing. The hand-built V10 significantly outmatched the highest-output factory powerplants available to buyers at the turn of the century.
Did you know? The designation “Boss 351” follows American automotive tradition by representing the engine’s displacement in cubic inches, totaling 5.75 liters.
Connection to the Secret Ford GT Project
The clandestine engine development coincided with work on another high-performance vehicle within the company. According to Kevin Byrd’s interview with Hot Rod, the creators of the V10 Mustang hoped to align their powertrain work with the development of the Ford GT, which remained a closely guarded corporate secret at the time. Official divisions such as Ford Racing and SVT held no involvement in the project, and the vehicle narrowly avoided being scrapped multiple times before its recent revival.
Frequently Asked Questions
What was the displacement of the Ford Mustang Boss 351 prototype?
The prototype featured a 5,752 cubic centimeter (5.8-liter) ten-cylinder engine.
How much power did the V10 Mustang produce?
According to dynamometer testing, the engine produced 510 horsepower at the wheels without any form of forced induction.
Was the Boss 351 V10 ever sold to the public?
No. The vehicle exists as a single prototype built by a group of six Ford employees without official corporate funding or production approval.
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