Ford Mustang Boss 429
Ford Mustang Boss 429
Photo: Charles from Port Chester, New York, CC0, via Wikimedia Commons
Vehicles · Vintage American Muscle

Ford Mustang Boss 429 · 1969–1970

The Boss 429 is a big-block SportsRoof Mustang built to homologate Ford's 429 'Boss 9' semi-hemi V8 for NASCAR, with the oversized race engine hand-installed by Kar Kraft in widened, shock-tower-relocated engine bays. Collectors prize it as the rarest and most powerful factory first-generation Mustang, valued for its NASCAR lineage, low production, and — for matching-numbers documented cars — blue-chip provenance.

The one to have: A documented, matching-numbers 1969 S-code car carrying its Kar Kraft KK serial and backed by an Elite Marti Report, wearing an original factory colour on the correct chrome Magnum 500 wheels. Best of all is a low-mile, unrestored survivor still on its original semi-hemi 429, Toploader four-speed, and buck tag.

Specification
Engine
429 semi-hemi V8
429 cu in (7.0 L) OHV 'Boss 9' V8, semi-hemispherical heads, single Holley 4-barrel
Output
375 hp (rated)
380 PS / 280 kW; 450 lb-ft at 3,400 rpm; peak 5,200 rpm; widely regarded as underrated
Weight
3,870 lb
1,755 kg curb; nose-heavy big-block in an intermediate pony-car body
Built
1,358
859 in 1969, 499 in 1970; Kar Kraft serials KK #1201–#2558
The market
Verified sales on file
5
May 2025 – Jun 2026
Median sale
$660k
all tracked results
★ Matching-numbers KK-serial survivor
$660k
median of 4 target-spec sales
Top result
$1.04M
Barrett-Jackson · Jun 2026
Benchmarks: driver $200k – clean/#2 $400k – concours & documented survivors $600k–1,045k · Trend: firming; documented matching-numbers survivors set records while modified cars lag

Know the real one

Every Boss 429 was a SportsRoof fastback finished by Kar Kraft in Brighton, Michigan: the shock towers were relocated, the front apron hand-fitted, and the battery moved to the trunk to clear the wide engine. The VIN 5th-digit 'Z' engine code and a KK serial (KK #1201–#2558) on the driver's door are the primary authentication.
The engine was homologated for NASCAR but never raced in a Mustang — it powered Ford's Torino Talladega on the superspeedways. Total Mustang production was 1,358 (859 in 1969, 499 in 1970); two Mercury Cougars also received the engine.
The 'Boss 9' is a unique semi-hemi with staggered valve covers, not the 385-series 429/460 nor the Chrysler 426 Hemi; most fakes hide a standard 429/460. Verify the KK number, an Elite Marti Report, the buck/door tags, and the engine build code (820-S then 820-T in 1969; 820-A in 1970, which ran a solid-lifter cam).
Matching-numbers, unrestored cars with documented KK/Marti provenance and original colour command the strongest money: a 4,435-mile survivor (KK #1412) became the first seven-figure Boss 429 in June 2026. Re-engined or modified cars — common, since the temperamental race motor was often swapped — trade for a fraction.

Verified sales · ★ = target spec · foreign results converted to USD as noted

DateVenueYearSpecMilesPriceLocNote
Jun 2026Barrett-Jackson1969matching-numbers S-code, KK #1412, Candy Apple Red, unrestored survivor ★4,435$1,045,000OHInaugural Columbus auction; 100-point Bob Perkins appraisal, original engine/gearbox/paint, buck and door tags. First seven-figure Boss 429 ($950,000 hammer, $1,045,000 with premium).
May 2026Mecum1969Raven Black fastback, 1 of 21 in the colour ★—$660,000INMecum Indianapolis; reported as a record for a 1969 Boss 429 at public auction, surpassing the prior $605k mark.
May 2026Mecum1970Grabber Green fastback, white interior, 1 of 9 in the colour combo ★—$660,000INMecum Indianapolis; rare Grabber Green/white combination drove a record 1970 result alongside the Raven Black 1969.
Oct 2025Mecum1969KK No. 2011, Candyapple Red fastback—$247,500INMecum Indy Fall Special; genuine Boss 429 donated by the seller, all proceeds to charity — price reflects the charity context, well below matching-numbers market.
May 2025Mecum1970numbers-matching 4-speed, Calypso Coral / white, 1 of 13 ★—$627,000INMecum Indianapolis; nut-and-bolt concours restoration. At the time the most expensive Boss 429 sold at public auction, any year.

Where to hunt

Bring a Trailer — Boss 429 resultsModel auction history and live listings Classic.com — Boss 429 marketAggregated sold prices and trend Glenmarch — Boss 429 resultsGlobal auction result database
Research file — market data verified through July 18, 2026. Sources: individually observed results via Classic.com feeds, BaT, Cars & Bids, Mecum, RM Sotheby's, Broad Arrow, Gooding, Collecting Cars, PCARMARKET and venue coverage, plus marque registries and factory press material.