Blast from the past: Considered too special for the crusher, members of the original Mustang Boss 351 Concept development team managed to store the prototype. (SAE)

Engineering artifact: Ford Mustang Boss 351 V10 Concept

A relic from the recently bygone era of naturally aspirated engine upsizing, the concept’s 5.8-L V10 was an exercise in bottom-up engineering.

Manufacturers are constantly prototyping by leveraging existing engineering assets to improve their products. Clean-sheet designs are expensive and rare, so advanced engineering departments are consistently tasked to unearth improvements with the lowest possible budget and manufacturing impacts. This process generates a steady stream of powertrain and vehicle prototypes, most of which never leave the digital realm. Those that escape the computer but fail to make production tend to meet a quickly recycled fate. Ford’s Mustang Boss 351 Concept is a rare exception.

Through some cunning and perhaps a little guile, the prototype Mustang V10 (top) first conceived in 2002 managed to elude the crusher, and 17 years later remains an impressive example of bottom-up engineering. Developed with real cost and production targets in mind, it was shepherded by a group of passionate and like-minded engineers. Were it not for the Great Recession and a sea-change in global vehicle-emissions targets, the new powertrain might have found a production home. Ford recently offered the chance to drive the prototype and speak with some of the team members behind it.

Optimizing existing assets
The Mustang Boss 351 Concept began in 2002 as a self-started powertrain project within Ford’s Powertrain Research & Advanced Engines group. The project was instigated and championed by a group of eight engineers, and the lack of a large, naturally aspirated performance engine in the Ford lineup at that time (such as Dodge possessed with the Viper) was a driving concern. The team started by considering variants to Ford’s modular V-engine architecture (aka the “Romeo” engine, from its production plant in Romeo, Michigan).

Ford already was producing a 6.8-L truck V10 based on the undersquare, taller-decked 90-degree 5.4-L V8, but it used an 18-degree split-journal crankshaft to provide the 72-degree even-firing sequence and required a balance shaft. The shorter-deck, shorter-stroke 4.6-L modular V8 had more revving potential. The team started with this engine, adding an additional cylinder in the middle of each side of the V8 block. A new V10 block was cast at Ford’s Casting Process Development Centre (CPDC) in Windsor, Ontario.

A common-pin crankshaft would be stronger for higher revving potential and wouldn’t require a balance shaft. This necessitated a 54-90-54-90 firing sequence with a custom billet crank machined for the build. The two additional cylinders brought total displacement to 5.8-liters (roughly 351 cubic inches), matching the namesake 1971 Boss 351 Mustang. The five-chamber cylinder heads were cast extensions of the aggressive 4-valve heads from the Mustang Cobra R, with custom billet camshafts.

At that time, a niche production line at Romeo already was producing lower-volume performance variants of the modular V8, so was a potential manufacturing outlet for the new V10. “We thought we could have a production variant through Romeo, maybe with a smaller displacement, cast iron, higher volume. It could be two-valve, or three-valve,” explained Kevin Byrd, supervisor, base-engine lower-end, at Ford’s Research and Advanced Engineering, and one of the original engineers on the project. “Then you could have your four-valve, more niche aluminum version for your high-end stuff. But all the engineering, a lot of your processes and components would be common.”

“You're working within some major constraints,” Byrd noted. “We had to figure out how to make a powertrain the company could afford, and then hope they would wrap a vehicle around it. If we had to spend a billion dollars on a plant, it wasn't ever gonna happen,” he said. “We had to do it in the smartest, most-economical way. It’s not much different from being on one of those cooking shows where they only give you so many ingredients. You have to use those ingredients, but somehow your meal comes out tasting awesome.”

A path to production
To have the all-new V10 engine considered, Byrd said the team understood they had to make it real to stakeholders, and the only way to do that was to get it in a vehicle. “That's when Jim [O’Neill] and his team really came to the rescue. Once the motor was coming together it's just a lump of metal. It needs a life. And Jim's team came with the stage,” Byrd said. “No one can stare at an engine and get a vibe, but they can drive a car and understand the thrill. It was a rolling rock stage.”

At the time, Jim O’Neill, now prototype build leader with Ford’s advanced powertrain R&D, provided a Cobra R mule based off a 1999 Mustang GT that was due to be crushed, which already sported a raised hood that would accommodate the custom Cobra R intake. Save for new engine mounts and front-suspension tuning to account for the heavier block (and moving the battery to the trunk), the V10 dropped into the Mustang’s engine bay. O’Neill said he and his team were thrilled to help move the cause forward: “It was a skunkworks project that had very little funding but a whole lot of passion behind it. No bosses, just a bunch of engineers building a car we all thought could go somewhere.”

The V10 makes the rounds
Once the vehicle was complete, internal promotion began in earnest. “Once the car was running, we took it over to a chassis dyno, got it running great and then just started passing the keys around,” Byrd said. “It went everywhere. The excitement shot all the way up to Bill Ford Jr.,” who according to O’Neill, drove the car multiple times, “We took it to every show we could possibly find at Ford,” O’Neill said. “Any place we could stick that thing and open the hood, we'd do it.”

According to Byrd, the canvassing had the desired effect. “It generated the excitement that we all thought it could. It really showed the people within Ford – not only at our level, but up through the management chain – the excitement for that performance and the opportunity to get in that space. The GT [supercar] was being formulated, so there was just a swirl of excitement of getting back into the GT range. We had the 5.4 supercharged motor option, now we had this V10 option. We had a lot of opportunities in that space, obviously,” Byrd added, “before the downturn.”

The Great Recession put the brakes on the entire industry. Ford was able to avoid bankruptcy and a federal bailout, but many programs were massively curtailed. The V10 program was just one casualty. “None of us had the heart to crush it,” O’Neill admitted about the concept car. “We hid it for many years in the back of different garages, we maintained it with no money, we did the work on it ourselves. We crushed a lot of cars over the years. This was one that we thought was so unique that it should stay.”

It’s a remarkable and fortunate preservation, as the Mustang Boss 351 Concept is a scintillating throwback to a non-turbocharged era. Compared to the latest hi-po version of Ford’s 5.0-L V8 (480 hp/358 kW), the 5.8L V10 produces around 500 hp (373 kW). It has a revvy, lightened-crank feel about it thanks to the Cobra R’s aggressive valvetrain and the custom billet cams and crankshaft. The V10 pulls hard from low rpm and revs freely, emitting a wicked and slightly exotic wail, like a slightly gruff V8 with dissonant harmonics that Viper owners would find familiar.

In the Mustang Concept, the V10 is paired to a now well-abused Tremec T-56 6-speed manual transmission, and puts power to the rear wheels via a Ford 9-inch axle and 3.83:1 final drive. It’s the kind of car you find yourself constantly ramping up through the gears and searching for tunnels or underpasses just to hear the ripping V10 snarl. Its sound is infectious, and at high rpm, you can feel the engine’s gyroscopic tug when modulating the throttle.

Enthusiasm as motivator
It would be understatement to say the team members we spoke with remember the project fondly. “I looked forward to coming in,” O’Neill recalled. “I don't ever remember one disagreement by anyone, and there were a lot of people that worked on that project – a lot of passion and emotion in it. And even when we broke it, we'd all get together, drag it back into the shop, and fix it and put it back out the next day. It was our choice, not our assignment.”

“Every program, you're constantly asking what if, and how? How do we get past this challenge? How do we make it better? How do we optimize it?” Byrd said. “And I think it made that group from many years ago still bond today. We still see each other in the hallway, and it's ‘click’, back to those times. I think in my 20 years, it's the coolest project for all those reasons. We weren't forced to do anything, everyone was there because they were excited.”

“It's a little bit disappointing it didn't go to production,” Byrd admitted, “but I tell people I make sandcastles on the beach, right on the shoreline. You build a sandcastle and it could be awesome. Then the tide comes in and washes it away and you go, ‘Well you know what, I get to build another one.’ So you move over 10 feet and you build another sand castle. It's the idea of building things that could be inspirational, could be breakthroughs. We build all day long and only some of it gets to go down the pipeline. But it's all cool.”

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