Mump 0406 05 Z Prototype Boss Ford Mustang V10 V10 Engine Bay
Dale Amy
June 1, 2004

There's a section buried deep within Ford Motor Company that could be thought of as the automotive equivalent of Kelly Johnson's infamous Lockheed Skunkworks: that secretive group responsible, over the years, for such leading-edge, outrageous aircraft as the U-2 and SR-71 spy planes. Ford's in-house skunkworks is called Powertrain Research & Advanced Engines, a hotbed of engineering experimentation that occasionally produces the most unlikely things, like an oh-so-subtle silver '99 GT wearing Boss 351 decals and packing an all-aluminum, short-deck, modular V-10, for instance.

What? A V-10 Mustang? Well, to be honest, the GT was just a handy-and very inconspicuous-place to stick the experimental engine for some road-going evaluation and development. This car's so discreet, a person could stand right beside it and have no clue he was next to one of the most powerful Mustangs to ever wear a manufacturer's license plate. Interestingly, this same GT played the role as test mule for the '00 Cobra R's 5.4L cammer engine a few years ago (explaining its R-model hood), but that's a story for another day.

The Boss 351 decals? We're coming to that, so be patient. First off, let's be 100 percent clear that the V-10 you're eyeballing shares nothing but its cylinder count with the 6.8L version found in Ford's Super Duty pickup and SUV lineup. The truck engine is based on the tall-deck 5.4L architecture, whereas this new one is essentially a Cobra 4.6L block wearing two extra cylinders. With the tight bore spacing on the 4.6L modular, adding those two pots increased block length by less than 4 inches, and, quite coincidentally, resulted in 351 cubic inches of displacement (281 plus 25 percent), finally explaining those 1971-vintage decals.

Retooling for such a block would normally cost big bucks, but the 351 V-10's costs were held in check by the inventiveness of the crew at Powertrain Research & Advanced Engines. The skinflint budget has been described to us as a "credit-card project." Under the supervision of project leader Kevin Byrd, these guys quite literally cut apart some existing 4.6L V-8 sand-casting cores and glued them back together in V-10 form, then repeated the process on some Cobra R head and lower intake cores (the intake had to be narrowed to fit the 4.6L deck height). They calculated the '00 Cobra R cam specs should be pretty close, so they had new, longer billet cams made up in that grind. And, since they retained the stock 4.6L bore and stroke, they were able to use '03 Terminator Cobra H-beam rods, connected to pistons of about 10:1 compression that "were lying around from another project."

Crankshaft design, again, bears no resemblance to the one in the truck 6.8L V-10. "The 6.8L truck crank," explains Kevin Byrd, "is a split-pin crank, like you'd find in a 60-degree V-6. [On the 351 V-10] we went to a common-pin design based off the Cobra crank, only instead of four pins, we've got five. The crank is set at 72-degree pin offset, but when you put that in a 90-degree block, it doesn't line up to a 72-degree firing. It ends up being a 90/54, 90/54, so you get that odd-fire sound, but it blends together really beautifully."

This odd-fire crankshaft created an interesting exhaust note, but also created a bit more work, since the crew couldn't just borrow a single EEC V processor from the even-fire 6.8L V-10. Instead, they had to use two such processors, each one calibrated to think it's controlling an inline five. This requires duplicate crank, cam, mass-air, and other sensors, and also necessitates the pair of 70mm throttle bodies that feed into those impressive-looking, black intake-plenum chambers.

In what may come as something of a surprise, fitting the 10-cylinder toy in the Mustang engine bay required only a tubular K-member and some handmade 5-into-3-into-1 headers. A look at our engine photo shows there's no lack of clearance up front, and that's with engine-to-firewall spacing remaining the same as a stock 4.6L. They backed it up with a T56 six-speed and a 9-inch rear axle and went out to play.

So how would this Boss 351 do if it ran up against a 1971 original? Nostalgically speaking, we're sad to report it would beat up the original and steal its lunch money. Though the '71 Boss was among the fastest of early Mustangs, with typical quarter-mile times in the high 13-second range, the V-10 version has gone as quickly as 11.93 seconds at 117 mph on Ford's Dearborn Proving Grounds.

Which leaves only one question: Why was the short-deck V-10 built? Credit-card project or not, Ford's engineers don't simply wander off on whatever tangent they want while on the payroll. Rest assured, there was method to this mechanical madness, as a larger displacement variant of this engine project was used last year in Ford's "427" concept car, and once again in "Project Daisy," the updated Shelby Cobra two-seater that wowed the crowds at this year's Detroit Auto Show.

As for its production line potential, nobody's talking. But we know it'll fit in a Mustang.