Nascar-engined Ford Mustang Boss 429 to sell at auction

Powerful, pristine pony looking for a new stable

If Ford’s Mustang was the original pony car, then the Boss 429 was its thoroughbred.

While visually similar to its Mustang siblings, the 429 was easily the most powerful stallion in the stable: adapted to take a Nascar-derived engine, its on-paper power rating of 375bhp was way below what actually came out of the engine on the road.

What’s more, it was arguably the high point of Mustang design, pairing on-tap power with aggressive yet understated styling – ditching much of the chrome toted by its contemporaries in favour of stencilled graphics and clean lines.

Built for just two years, few remain today in good condition – making this 429, heading to auction at Mecum’s Houston sale, a rare horse indeed.

Winning formula

Ford’s first Mustang surfaced in 1965, inaugurating the idea of the pony car: a class of affordable machines equipped with long noses, sports performance and rear-wheel drive power.

The formula proved a runaway success, with sales of the first Mustang breaking records for Ford.

Rapid growth

Over the following years, the Mustang returned in many iterations, bearing a raft of upgrades – from bigger engines to increasingly bigger bodies. By 1970, the Mustang had grown larger, heavier and altogether more aggressive.

Ready testbed

With an established and popular platform at their disposal, when the time came in the late-’60s to homologate a newly developed Nascar engine, Ford determined that the Mustang would be the perfect pony to bear the load.

Made to fit

The race-bred Boss 429 engine was the most powerful Ford had built to date – and it was also too huge for the Mustang’s frame. As a result, ‘Stangs selected for the performance package were pulled off the line and sent to Kar Kraft in Michigan.

Special division

Kar Kraft functioned as something of an in-house developmental tuning shop for Ford, and it was here that Mustangs were modified to take the massive ‘shotgun’ motor.

Front heavy

This packing job meant not just cutting out a hole big enough for the block, but also repositioning internal components (the battery went to the back) and fitting a sway bar – a first in a Mustang – to counteract the sheer weight in the nose.

Not for looks

A functioning hood scoop was also added to the Boss 429 to provide much-needed cooling airflow to the racing engine. The vent was controlled manually from the cabin, to be closed by the driver when driving in the rain.

Little white lies

The result? On paper, it was pretty disappointing: Ford, it seems, under-rated the 429’s power in order to circumvent insurance costs and growing pollution fears.

Dealers marketed the new Nascar-engined pony car as a 375bhp machine with 450 lb/ft of torque.

Marketing flop

Not too shabby, perhaps, but a hefty price hike for the performance upgrade took the 429 into Stingray territory – and with that under-sold horsepower figure, the Boss struggled on forecourts, leading to its limited production lifespan.

More for the taking

Those that did shell out, though, got a factory-detuned muscle car that, with a few tweaks to take it back to stock and the smog pump bypassed, could readily exceed 500bhp on the street – with reports that it could hit 175mph in the right conditions.

Track on tap

The 429 also benefited from a host of racing parts, including competition suspension, that made it more than ready for weekend track visits – though its rarity today means that accurate racing performance figures are hard to come by.

Ready for the road

Despite the power under the hood, the 429 was also pretty friendly as a day-to-day runner (even with the 4-speed Toploader transmission), thanks to power steering, that sway bar keeping things smooth and an engine that was surprisingly happy to cruise at high revs.

Early engine

This particular Boss 429, built in 1969, is one of just 279 to carry the first-generation 820-S Nascar engine. Later models carried either the quick-revving 820-T or lighter 820-A block with its mechanical cam setup.

Matching numbers

It’s also one of only 132 Mustangs to carry a Royal Maroon finish, and has been restored to Concours standard – making it a stunning matching-numbers example, both inside and out.

Factory parts

Despite that restoration, it mercifully remains a highly original machine, carrying a host of period parts – including the front suspension and rear sway bar, as well as a factory smog pump, exhaust manifold and carburettor.

Stamped all round

It’s also peppered with identifiers, including the original vehicle ID tag, Kar Kraft sticker and body-stamped VIN numbers to prove its provenance as one of the mightiest Mustangs around.

Hot lot

Understated, tastefully restored and free from modern modifications, this is a pristine illustration of arguably the greatest iteration of the Mustang – and you can expect it to head for the $200,000 (£143,000) mark when it goes to auction in Houston tomorrow (7 April).