Tom Shaw
August 10, 2016

“Whos the !@#$% who did this,” thought Joe Flowers, examining a hatchet job done on his rare Boss 429 breather. He had just discovered that the Ram Air flapper on his newly purchased 1969 Boss 429 Mustang had been cut away. He knew this was not stock and was not happy. It was 1978. Disco was in, and muscle cars were out, but not for Flowers. He was a big fan of Detroit iron and was always scanning backyards, garages, parking lots—ever on the lookout for his next find. His new Boss 429 came to him on just such a mission. He had been driving past the Lincoln-Mercury dealership in Medina, Ohio, the next town over from his hometown. Buried deep behind everything else at the Lincoln-Mercury dealership, a familiar shape caught his eye. “I knew exactly what it was by the hood scoop,” Flowers says.

“I stopped in and asked them if that car was for sale.” They told him the car belonged to the dealership owner’s son, and they weren’t sure if it was for sale or not. “Come back tomorrow,” they told him. Flowers did. “Yeah it’s for sale,” he confirmed. “Go to my house. It’s sitting inside the barn with the keys in it.” It’s crazy, but the guy was sending him to his house to take it for a test drive. Flowers did and liked the car. “I made an offer, and in less than a week, I had the car,” he says. The kid’s dad wanted him to sell it because he was afraid his son was over his head in the monstrously powerful Mustang. The Wimbledon White Boss 429 had only 11,000 miles and appeared—other than a set of Cragar SS wheels—very original. That was good news, but even better news awaited.

“It sounded pretty radical,” says Flowers, who also owned a Grabber Blue 1970 Boss 429. Investigating his new purchase, he noticed the engine made some departures from factory stock, such as a set of highly engineered headers engraved with “Larsen Engineering” and a deep sump oil pan. But no story came along with the car, so its mods were a mystery. Then, the mystery was answered.

“I took it to SAAC 8 in Dearborn, Michigan,” Flowers says. “It was near the end of the show and everybody was getting ready to leave. My car was lined up with three or four nearly identical white Boss cars lined up—you couldn’t tell which one was which. However, a kid was walking by the cars and going up to the front fenders and feeling under there. Then he’d go to the next one and feel under it. He feels under my car and looks over at his dad says, ‘Dad, here it is!’ I asked his dad what it was all about.”

“That’s Leonard Adamek’s car, the first owner,” the guy said. “We did all kinds of work on it. I have a tape of that motor on a dyno. We balanced and blueprinted it. I know it’s the car because when we were working on it, we dropped it onto a jackstand. Feel under the fender; it’s got a dent from the jackstand.” Sure enough, it did. And it does to this day. Flowers left SAAC 8 with Leonard Adamek’s phone number and the tantalizing tip of a story about his Boss 429.

Shortly after, Adamek told him the tale. “Back in 1969, Adamek was a co-op college student part-timing at Ford. He went into Stark-Hickey West, bought the car off the showroom floor, and then he had to take it home because it was wintertime. When the weather turned nice, he started driving it, but he was real unsatisfied with the performance of the car. He writes Bunkie Knudsen [president of Ford at the time] a real nasty letter telling him how unhappy he is with the car’s performance. ‘I never thought they could find me because I was a college co-op student. I wasn’t on the directory,’ he said. ‘But they sent Jacque Passino looking for me, who found me, and took me up to Knudsen’s office. We had a discussion for about an hour about the car.’”

Knudsen wasn’t harsh with the young complainant. Instead, Knudsen wanted details on why Boss 429, one of Knudsen’s pet projects, was a letdown. “They asked what I wanted it to do,” Adamek said. “And if they could borrow the car, do some modifications, and make it perform.” Of course, he agreed. “They had the car for about a month. When they called and told him the car was done, he went to Dearborn Steel Tubing [a Ford sub-contractor] to pick it up. When he picked it up, it had two brand-new cylinder heads in the box in the trunk as a gift. He was a very happy man, thereafter.”

Adamek then gave the car the VIP treatment for the rest of the time he owned it. “He told me he never ran the car in water, it never saw any kind of weather,” Flowers says. But Adamek wasn’t the only one who admired it. “Around 1976, a guy in the truck division kept bugging him to buy the car.” He finally sold it to him with the understanding that he could buy it back if he wanted to. “A year later, he wanted to buy the car back, but the guy had already sold it,” Flowers says.

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From there, it went through a quick succession of owners, all of whom kept the Mustang nice but didn’t keep it long. Flowers further learned that Knudsen had an ulterior purpose for the Boss 429’s makeover. The revisions were being considered to pump up the 1970 production. In the end, the company decided Boss 429 production was too close to its end to do a big change. Instead, on June 25, 1969, Ford mailed a letter to Boss 429 owners. “Rather than produce an all-out fire breather for street use, Ford engineers put together the best combination of smooth action, inclement weather drivability, quiet operation, and performance possible for normal operation.”

“Some owners have expressed a desire to increase the performance of their 429 Boss,” the letter added. “Accordingly, we have just made available through your Ford dealer a new mechanical camshaft and tappets which have given an improvement of up to 25 horsepower, plus 1 second and 5 miles per hour in our quarter-mile tests.” This is the car those experiments were done on, though Flowers didn’t realize it right away. That’s why the hood scoop flapper was cut out. Not realizing its significance, he pulled the modified breather off and sold it at a swap meet.

Ford published its recipe for modding the Boss 429, learned from experimenting on Flower’s car, in the August 1969 issue of Shop Tips. One of the recommended mods was to cut the flapper out and open up the hood scoop. “When I found out what the car was, I knew selling that breather was a mistake. In retrospect, we can see this is how the engine should have been configured from day one. Detuning it to be happy as a driver was a mistake. If you’re going to build an exotic, it should live up to its promise. This one does. This car has a lot more horsepower, it breathes a lot quicker, and accelerates quicker,” Flowers says. “The 4.30 gear has a lot to do with it. The 3.91 gear makes the car kind of bog because it doesn’t rev quick enough. It’s got plenty of power to get it going, plenty of power.”

Driving the Boss

During our photo shoot, we piled into Flower’s unique Boss ’9 and took a 16-mile ride down the turnpike to the exit where we took these pictures. The Boss 429 negotiates mundane low-speed chores without drama. Accelerating onto the express lane, things change.

At highway speeds, the 4.30:1 axle has the engine revving, but it doesn’t seem to mind. Sixty-five mph is taching around 3,500rpm. The engine is heard, but the noise is not overpowering. We chat about the Boss 429’s power for a bit, then Flowers gets into the throttle. The Boss ’9 surges ahead, with no cough, chug, or flat spot. We pass 70, then 80mph. It feels like the engine is just getting started, so he stays in it. Now, we’re doing 90 and climbing. The engine was designed for NASCAR’s high speeds. At the triple-digit mark the car still feels stable. The tach reads about 5,800rpm, and there’s plenty left. He isn’t afraid to run the car, and the car isn’t afraid to run. The Boss 429 is a racehorse bred, groomed, and trained for the track, and finally, unleashed for its showing at the derby.

“I had it on Ford’s Utica test track,” Flowers says. “The car never stopped pulling. I went down that straightaway, and it was still pulling by the time I got to the turn. I had to let up. You can be doing 110 and kick it, and it’ll pick the front end back up.” Flowers didn’t know it at the time, but he’s caretaker of a national treasure. It’s the Boss 429 that every Boss 429 should have been—radical, rowdy, butt-kickin’, solid-lifter, quick-revving, and super-powered. It’s the Boss 429 that we knew lived deep inside the Boss 429. So good to finally meet you.

Boss 429 Hop-Ups From the August 1969 Shop Tips:

Shop Tips was a magazine that Ford produced and sent to its dealers. Targeted primarily towards the dealerships’ parts and service departments, it focused on service procedures and marketing service parts. The August 1969 issue focused on Boss 302 and 429 Mustangs. It’s where Ford published its findings about modifying the Boss 429, learned from working on Joe Flower’s car. Date codes on his exhaust system precede this issue. The following is what this issue had to say:

Strip Tips for Quick Trippers

ENGINE: Here are some touch-up tricks that will give you the ultimate output from the Boss 429.

• FOR THE C9AZ-6250-A HYDRAULIC CAM—Back off the rocker arm adjusting screw (with the lifter on the base circle of the cam) until the push rods are free to turn, then tighten a quarter turn. This will prevent tappets from pumping up, and will raise valve toss speed of the engine.
• FOR THE D0AZ-6250-D MECHANICAL CAM—Remember that the aluminum cylinder heads grow as they warm up, causing quite a change in the valve lash (hot vs. cold). Set valves at 0.013” cold or at 0.024” hot.
• Install lightweight, fabricated exhaust headers. Try 34-inch primary tubes into the collectors. Make collectors of 2 1/8-inch O.D. material for street use, or 2 1/2-inch for strip. Headers are available from Larson Engineering, 26121 Van Born Road, Taylor, Michigan, 48180.
• Use a reduced-pitch flex-blade fan, or one with decreased diameter.
• Use solid-core ignition wire in place of the standard radio-suppression type. Autolite Steelductor Silicone cable and connectors work well, and are heat resistant also.
• Block the heat riser passage. This will cause the mixture to run cooler and produce more power.
• Install the deep sump oil pan and extra-long oil pickup.
• Use #84 secondary carburetor jets with standard exhaust, or #86s with headers and open exhaust.
• Disconnect the power steering pump drive belt.
• (STREET) Set the distributor initial advance at 12-14 degrees. With the maximum internal advance of 20 degrees at 3,200 engine rpm, this will give a maximum advance of 32-34 degrees. (STRIP) Use C3AZ-12171-A breaker points (2 sets) and check for 32 ounces of tension. These are low-mass points to prevent point bounce, but they also have a high wear rate. Remove the vacuum hoses and plug the openings. Try 10-14 degrees initial spark advance. Check distributor to desired rpm on distributor machine. Maximum safe advance is 38 degrees. Retard spark as necessary to prevent pre-ignition damage to the aluminum pistons and cylinder heads.
• Open up the hood scoop for increased airflow. To do this, remove the scoop from the vehicle, and cut away the front part of the fiberglass inner panel which seals on the air cleaner tray. Reinstall the scoop.
• Use Autolite AF-22 spark plugs for strip, AF-32s for street. Set gap at .032-.036.
• Install a 5-6 psi electric fuel pump at the tank.
• Use the highest-octane fuel available.

Drive Line

• Remove teeth on second and third gear blocker rings, for faster power shifting.
• Install 4.57:1 ratio ring and pinion, along with a Detroit Automotive Locker.
• Install 7-inch slicks on rear.


• Install 302 CID Mustang front springs.
• Install 90/10 uplock front shocks and reinforce the shock absorber brackets.
• Install a good set of traction bars on the rear axle.