“Bunkie” Knudson and Larry Shinod were both stolen away by Ford after doing so well with General Motors. They were tasked to put a plan in action that would dominate the SCCA championships. The final result of the plan was a Mustang that accomplished their goals they set. The plan which ultimately spawned the Boss 302 and Boss 429. While the Boss 429 was produced in a bid to homologate Ford’s new 429 cubic-inch powerplant for future use within NASCAR racing, the Boss 302 was designed with the sole intent of outright domination of Trans-Am class racing.
The Boss 302 was released to a significant degree of fanfare in 1969 and returned for a second production run in 1970. Competing alongside the recently-released 1970 Dodge Challenger (and its updated E-body cousin, the 1970 Plymouth Barracuda), the Boss 302 was a necessary stablemate for Ford. However, the 1970 production year would prove to be the last for the Boss 302, as it would be dropped by Ford, before its junior year. In actuality, little changed between the Boss 302’s two years of production, aside from a few minor suspension revisions, and a handful of modest exterior modifications.
1969 Boss 302
Boss 302 became the first Mustang to use the Cleveland heads, years before they would see regular production.
- A strengthened engine block
- 8 valve cover bolts (instead of the usual 6)
- High-strength steel connecting rods
- Smaller spark plugs (made more room for the valves)
Though the Boss 302’s official horsepower is listed at 290, most put it much higher than that. One Ford engineer, Bill Barr, dynoed the engine at 314 hp with all equipment, and 390 when stripped down. It was common for manufacturers to understate the horsepower capabilities of their engines. This was a maneuver designed to keep the insurance companies at bay.
- 4” bore x 3” stroke
- 2.23” intake valves
- 1.71” exhaust valves
- High-lift camshaft
- Forged steel crankshaft
- Holley 780 cfm 4-barrel carburetor
Transmission and Rear End
The Boss 302’s transmission was a standard 4-speed toploader, available in a close or wide-ratio. No automatic transmission options were offered for the Boss Mustangs.
From there, Boss 302 owners had their choice of several desirable rear gear axles. The standard was a durable 3.50 with an open differential. They could also select a 3.50 with a limited-slip differential (traction-lok), or a 3.91 limited-slip. The final rear gear option was a 4.30 with a Detroit no-spin differential. This last option was a locking differential, most appropriate for race cars.
Suspension
The Boss 302 was quickly labeled “the best handling Mustang yet” by Car and Driver. It achieved this by having an exceptional suspension. Extra bracing on the shock towers, stiffer springs and shocks, and staggered rear shocks delivered improved handling.
Though an 0.85” stabilizer bar was slated to be used, it was swapped out in favor of a 0.72” front sway bar.
Manual steering and front disc brakes finished the handling adjustments. One engineer remarked that the secret to the Boss 302’s handling was minor adjustments. For the most part, it had the same suspension geometry as a standard Mustang.
Exhaust
Naturally, a great sound was important to drivers. New manifolds were designed to go with the Cleveland heads. A transverse muffler system helped add uniqueness to the exhaust note.
Wheels and Tires
All Boss Mustangs came with Magnum 500 chrome wheels. Superfat wide oval F60x15 bias-ply tires were chosen to accompany these wheels. The result was a widebody look. The fender arches had to be increased to provide enough clearance. Improved front spindles were also added to enhance the cornering capability.
The Mustang Boss 302’s hood is painted with matte black paint to eliminate glare. It also received a standard chin spoiler to help reduce aerodynamic drag. The Boss 302’s side stripe contained its name, though it served no practical purpose.
A rear wing and rear window louvers were sporty options that could be added. They came in the same anti-glare black as the hood.
The Boss 429
Engine Configuration
The Ford Boss 429 engine is a V8 engine that features a unique and powerful configuration. Here are the key details:
Engine Type: V8
Displacement: 429 cubic inches (7.0 liters)
Bore x Stroke: 4.36 x 3.59 inches
Compression Ratio: 11.3:1
Fuel Delivery: Holley 4-barrel carburetor
Valvetrain: Overhead valve (OHV)
Number of Valves: 16
Max Power: 375 horsepower
Max Torque: 450 lb-ft
The engine’s large displacement and high compression ratio contribute to its impressive power output. The Holley 4-barrel carburetor ensures efficient fuel delivery, while the overhead valve design and 16 valves allow for optimal airflow and performance.
Engine Specifications Values
Engine Type V8
Displacement 429 cubic inches (7.0 liters)
Bore x Stroke 4.36 x 3.59 inches
Compression Ratio 11.3:1
Fuel Delivery Holley 4-barrel carburetor
Valvetrain Overhead valve (OHV)
Number of Valves 16
Max Power 375 horsepower
Max Torque 450 lb-ft
The Ford Boss 429 engine’s specifications highlight its impressive performance capabilities and its place in automotive history. Whether it was dominating the racetrack or powering high-performance street cars, this engine remains a symbol of power and engineering excellence
Such a large big block engine made the car nose heavy. To help offset this, the battery was relocated to the trunk, and a 3/4″ sway bar was added to the rear end to limit body roll. This was the first Mustang ever fitted with a rear sway bar, giving it better handling than the other large engine Mustangs of the time, making it a much more capable track car. So did an oil cooler which allowed both high RPM and endurance loads on the engine, and a manually controlled hood scoop for bringing in denser air for more thorough combustion. For better ground clearance the front spoiler was made shallower than the Boss 302’s, and a 3.91 ratio rear axle came with a “Traction-Lock” limited slip differential. Other features included color keyed dual racing mirrors, an 8,000rpm tachometer, and AM only radio.[citation needed]
A total of 1359 original Boss 429s were made.
1969 vs 1970 Boss 302 Mustangs
There were several small changes made between 1969 and 1970 for the Boss 302 Mustang. The only performance-related change was to the suspension. Ford added a rear sway bar, which allowed them to upgrade the front sway bar to the originally-planned 0.85” one.
You could also get an optional Shaker hood scoop for the Boss 302 in 1970. Other than that, the changes were all aesthetics.
While the 1969 Mustang Boss 302 featured a bold “C” shaped side-decal, the 1970 version featured a hockey-stick shape. The purpose for this was simple, the stripe came up and joined the (now slimmer) hood stripe.
Color options were also significantly expanded for 1970. The 1969 Boss 302 Mustang came in Bright Yellow, Calypso Coral, Wimbledon White, or Acapulco Blue. For 1970, these options expanded to include many more colors.
Buying a Used Boss 302
It’s difficult, and expensive, to find a used Boss 302 Mustang. Even though 8,642 were created, most were driven hard and gave up the ghost a while back. As of 2019, Hagerty evaluated a1969 Boss 302 in perfect condition as being worth $135,000. They also determined that this would be the most valuable of the Boss 302 Mustangs given its scarcity.
While $135,000 for a collectors’ car is pretty acceptable, not a lot of people have the opportunity or the cash for that kind of investment. Most people who admire the Boss 302’s performance or appearance opt to create their own via the aftermarket.
Honestly, Larry Shinoda would be ecstatic to know his work continues to inspire people to go out and add some neat things to their Mustang.
Whether you decide to drop in a full Boss 302 crate engine or just add some heavy-duty suspension components, you’ll be making a Mustang that’s a half-step closer to the Boss 302.
For extensive information on the 71 Boss 351 click here to the 1971 production and specs research.
The Last Boss, 1971 Boss 351
The engine displacement number, it fell somewhere between the 302 and 429, combining their strengths. The 302 was more of a road-course car, while the 429 was a straight-line brute on the dragstrip. The 351 met them in the middle.
Unlike the 302, which had a Windsor block and Cleveland heads, the entire Cleveland engine was used instead. The stroke difference between the two engines amounted to half an inch, increasing the Boss 351’s compression ratio. In order to improve the performance of the Boss 351, it was also upgraded in several other ways, including upgrading the pistons to forged aluminum and adding four-bolt mains to the block. All told, the 351 delivered at least 330 horses and 370 lb-ft of torque, enough to outgun a number of big-blocks.
The Boss 351 was built for just one year, with only 1,806 units produced—slightly more than the Boss 429. In addition to a Hurst shifter, the package included a competition-grade suspension and power front disc brakes. The end result was a car that could go from 0-60 in a snappy 5.8 seconds, with better handling and braking than either of the other two Boss Mustangs’
The 1971 Boss 351 replaced the previous Bosses and became known as the performance Mustang. There were 1,806 of these special cars made. They came with very few options, including:
Boss engine,
ram air,
3.91 rear axle,
traction-loc,
4 speed manual transmission,
competition suspension,
Front power disc brakes
Front spoiler,
Mach 1 front grill
Mach 1 lower body side paint
351 decals and tape treatment,
Chrome front bumper
Hood that was mostly blacked out.
15×7 wheels and chrome trim rings
Goodyear F60x15 RWL tires
The original Boss of 1969-70, the Boss 302, was a homologation model, produced to meet the eligibility requirements of the SCCA Trans-Am series. It used a high-revving 302-cid V-8 rated at 290 horsepower, built to meet the race series’ five-liter class limit.
Ford, however, had ended its Trans-Am program by the time the bigger, heavier Boss 351 arrived late in the 1971 model year. Though it lacked a racing pedigree, the new Boss turned out to be one of the fastest Mustangs of the day. It was also one of the rarest, with just 1,806 built.
“The Boss 351 was more drag-racing oriented than the Boss 302, but better handling than the 429 Cobra Jet,” said Mike Berardi, global director of service engineering operations at Ford Motor. A red Boss 351 is one of 55 Mustangs in his collection, and a favorite to drive. “It’s high revving, so you row the gears more than with a 429 CJ,” he said.
The 351 in the ’71 Boss was Ford’s 351-cid Cleveland engine, nicknamed for the Ohio plant that built it. The 351C shared little more than bore and stroke spacing dimensions with the 351 Windsor used in the 1969 Mustang. Its advantage was deeper breathing, a result of huge ports and valves in the cylinder heads. The 1969-70 Boss 302 had married the Windsor block with Cleveland heads, but the Boss 351 was the whole deal, with lots more torque.
Starting with the 11:1-compression 351C with four-barrel carburetor, Ford assembled a top wish list: four-bolt mains; forged pistons; shot-peened connecting rods; high-lift camshaft; aluminum intake with 750-cfm carburetor; dual-point ignition and ram air induction. It added up to 330 horsepower at 5,400 rpm and 370 pound-feet of torque at 4,000 rpm, matching Chevy’s LT-1 350 in the 1971 Camaro Z28. Magazines that tested the Boss 351 posted quarter-mile times in the low-14-second range at about 100 mph, on par with big-block models like the Mustang 429 CJ.