Ford's secret V10 Mustang is back, with 517 hp at the wheels
Five engineers, one V10 and 17 years in the back of a garage
Ford's Heritage Fleet has put its one-off V10 Mustang back on the road, 24 years after a group of engineers started building it in their own time. The car is a 1999 Mustang GT with a naturally aspirated 5.8-litre V10 where the 4.6-litre V8 used to sit. It exists today only because the men who built it decided Ford was not going to crush it.
Ford had no answer to the Dodge Viper, so eight engineers cast a V10
The project started in 2002 inside Ford's Powertrain Research and Advanced Engines group, and the driving concern was that Ford had no large naturally aspirated performance engine at a time when Dodge had the Viper. The answer was not a V8 with two cylinders added on the end. Ford's Casting Process Development Centre in Windsor, Ontario cast an entirely new 90-degree block, with the extra cylinder dropped into the middle of each bank of the 4.6-litre Modular V8. That took it to 5.8 litres, or 351 cubic inches, which is where the Boss 351 name comes from.
Two engine computers, because nothing could fire a 54-90-54-90 V10
The five-chamber heads were cast extensions of the four-valve Cobra R design, with billet camshafts and a billet crankshaft. The team wanted a common-pin crank, which is stronger and revs harder than the split-journal item in Ford's 6.8-litre truck V10 and needs no balance shaft, and paid for it with an odd firing sequence of 54-90-54-90 degrees. In 2002 Ford had no control module that could manage that, so the engine runs as two independent inline-fives sharing a crankshaft, each with its own module and its own throttle body. Behind it sit a Tremec T-56 six-speed manual and a 9-inch axle with a 3.83:1 final drive, in a Cobra R mule that had already been booked in for the crusher.
Jim O'Neill's team hid the Mustang and paid for its upkeep
The Great Recession killed the programme, and Ford scrapped a great many prototypes in those years. This one survived because the engineers would not hand it over. Jim O'Neill, now prototype build leader in Ford's advanced powertrain R&D, has described moving the car between the backs of different garages: “we maintained it with no money, we did the work on it ourselves”. It stayed out of sight until 2019, when Ford finally let outsiders drive it. Naturally aspirated V10s did not become normal either, and the ones still being built, such as the Cosworth in Adrian Newey's track-only Red Bull RB17, are not road cars.
Ford's dyno now reads more than 517 hp at the wheels, up from 432
The Heritage Fleet worked with members of the original team to recommission the car, replacing aged electronics and going back through systems nobody had touched in decades. Then Ford strapped it to a chassis dyno, where it recorded more than 517 hp at the wheels against roughly 432 hp when the car was new, a gain of close to 20%. The engine was quoted at around 507 hp at the crank in its original form, which lines up with that early wheel figure once driveline losses are taken out. The visible difference on the car today is a modernised intake. For scale, Ford's own parts counter will now sell a Mustang owner more than 800 hp with the warranty intact.
The US Heritage Fleet holds 175 cars, and Europe had one first
The operation doing this work is new. Ford has run heritage collections in the UK, Germany and Australia for years, but the American fleet was only formalised under chief executive Jim Farley. It now holds around 175 vehicles, roughly 50 of them on display at the Dearborn headquarters, and it is set up as an internal resource rather than a museum: designers and engineers are brought in to look at the cars, and they get taken out to events such as the Woodward Dream Cruise. A running prototype nobody outside Ford could have seen for most of two decades is exactly the argument for the whole exercise.
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The Boss 351 did not lose an engineering argument. Ford's own people had a 6.4-litre version of this V10, good for more than 600 hp, on the table as a candidate for the second-generation Ford GT, and the car that reached production used a 3.5-litre twin-turbo V6 instead. The V10 lost to a recession and then to a downsizing rulebook, which is not the same as losing on merit. Ford is currently willing to stretch the Mustang name onto a four-door hybrid, so a ten-cylinder coupé was never the strangest idea in the building.
It also settles what a heritage fleet is for. A parked prototype is a photograph. A recommissioned one produced a number nobody had, and that number is higher than anything Ford ever measured from the car while the programme was alive. There are around 175 vehicles in the American collection and about 50 of them on show in Dearborn. The measure of the thing is how many of the rest get started, not how many get dusted.
