Jon Kaase’s 2008 Ford Mustang Blue Crescent Beheader

By Ro McGonegal
Photography by Robert McGaffin


“I have always wanted a Boss 429 Mustang because I consider it to be Ford’s masterpiece of engineering. The problem is, considering their present value [approximately $500K], I was as far away from being able to afford one in 1969 as I am today. If I could buy an original, it would be far too valuable to drive. With the release of our Boss Hemi engine parts, the next logical step was to build our own version, rationalizing that a complete running car would showcase the new parts and create a new market for our parts sales,” said the gleeful Jon Kaase.

Original cars had a working hood scoop. Kaase wanted to stay away from that, so he used a NASCAR-flavored BSR air cleaner and bottom plate that drops the whole assembly cleanly away from the underside of the hood. Big Boss is nearly 600 ci large. Kaase’s pal Chuck Lawrence did all the wiring and considerable finessing needed to make it all work

“Let’s be honest here. I wanted this car! I want to drive it home and give my family and neighbors a ride. Most of them think I have a garage that does quick oil changes. They have no idea. I hadn’t driven anything with over 360hp since 1974. With 800 ft-lbs of torque and 900 hp, this car is a real handful.”

We were yakking with Jon at the recent PRI show about the black beast in his booth. Then the thread wound into a trip we’d made to his old shop a dozen years past. We had gone there to document the building of an 812-inch IHRA Pro Stock motor. Forgot what it made, something like 1,400 on the motor. Kaase said that times have changed, drastically, and that same configuration outfitted with the latest parts would put out at least 1,900. We’ll come back to this in a minute.

Look at the Boss Nine Mustang. Kaase’s vision was based on a stock-appearing car, one that you would buy from a dealer with the biggest motor available. It was rated at a paltry 375 hp. Kaase’s version makes 900. In the day, the 1969-70 Boss 429 came with 7-inch Magnum 500 rims and F60 Goodyear Polyglas GT rubber, and perhaps the most arresting thing about it was the distinct lack of stripes, black-out trim, wheel or rocker panel moldings, or chrome exhaust tips. All it said was “Boss 429” on the fenders, and it carried a functional hood scoop that practically disappeared when the body wore dark livery. Kaase’s Boss Nine fairly reeks that aura and looks for all the world like it just rolled off the Kar Kraft (Brighton, Michigan) “assembly” line, modern Magnum rims and all.

Part of that image comes from a new Mustang that Kaase bought from B.F. Evans Ford in Livermore, Kentucky. It had but 180 miles on the odometer, and only because Evans’ guys drove it to Nashville, where Kaase’s guys loaded it on a trailer for the final miles home. All the build tags and stickers are still in place, adding to the dj vu mystique. “It was worth it because it’s new and it’s a pleasure to work on, no dirt, oil, or road gunk,” quipped the low-key Kaase.

The biggest obstacle for Kar Kraft was that skinny space between the shock towers, a place never meant for an engine with the girth of the Boss (see “Total Performance,” p. 44). Their techs had to cut out, rebuild, and relocate the towers to make room for the big Blue Crescent (semi-hemispherical combustion chambers) cylinder heads, and with little space to spare even at that. Kar Kraft also lowered the suspension by about an inch, using control arms and spindles specific to the Boss 429. We asked Jon about how the Boss Nine fit in that modern engine compartment. He smiled, Cheshire cat-like. “You could say it just sort of fell in there. We didn’t have to trim, cut, or rebuild anything for it to take the motor. We didn’t even have to take the hood off.”

As a work in progress, the Mustang chassis/suspension is bone stock. The Boss Nine is equipped with latter-day 18-inch American Muscle Magnum 500 wheels and thick Pirelli PZero Rosso rubber, but the motor has enough moxie to break ’em in fourth gear

Then: “I should have measured the stock engine crank centerline at the front, with respect to the sides. The tailshaft and rear crossmember measured to be in the centerline of the car, and the pinion is also centered between the wheels. The thing is, I remember the valve covers to be unequal distances from the shock towers, offset to the right. Is the engine in these [new] cars at an angle? With the Boss engine in place, the tailshaft is centered and the valve covers are closer to the right, just like stock.

“This car is a natural for the Boss Hemi swap. There is plenty of room between the shock towers, enough room for headers [you can reach past them with your hand], and enough room between the accessory drives and the radiator. The hood needs no modification for the air filter. It’s close, but the right filter assembly will fit. A stock rear sump Moroso pan fits over the steering and crossmember perfectly. The cooling system is completely stock. All we did was space the bottom of the core outward an inch or so, but the top of the radiator is in the stock location.”

D&D Performance supplied the blast-shield/bellhousing and the Viperized T56. Kaase made the crossmember. The McLeod clutch assembly is twin-disc on an 11-inch steel flywheel

Kaase stripped it down and installed a mock-up engine, then sent it to fabricator pal Chuck Lawrence in Hiram, Georgia, for motor mounts and headers. Back at Jon’s shop, they built and dyno tested the 589 and installed it with the clutch, transmission, and driveshaft. It went over to Lawrence’s for the close-up work–hoses, wiring, gauges, and the rest of the finish work.

Kaase: “The front drive is from Billet Specialties. It comes with a billet front cover, which has extra bosses for attaching the accessories and brackets. It comes with the front cover, water pump, power steering pump, an alternator, A/C compressor, and all the pulleys and brackets. Nothing bolts to the heads. As complicated as it looks, it only took an hour to completely assemble it. Like any good racers, we threw the instructions out and just winged it. I was really impressed with the quality and fit of this assembly.”

As the Boss 302 was created to champion small-block performance and to rub fenders with the Chevrolet Z28 in the Trans Am series, in the big-block world, the Boss 429 was really a homologation special required for legality in NASCAR. Production for ’69 was 859 units (including two Boss 429 Cougars). In ’70, the total was but 499. Automatic transmission and air conditioning were not offered, but at least it had an engine oil cooler and the battery was moved to the trunk, largely to free up space in the motor room. Well, they still don’t race Mustangs in NASCAR, so how come it wound up in one instead of the obvious Torino? Sorry, we can only guess at the back story on this one, but Ford marketers figured heavily on boosting the Mustang’s image, so that’s the way it was.

About as slick as a moleskin biscuit, the Boss Nine has every bit of its assembly line interior. Colorful it ain’t; functional it is. Note the just-the-right-height Hurst gear changer

Kaase’s remarks about the efficacy of modern speed parts made us think. The Boss 429 had huge ports and a marginal camshaft that really didn’t take effect until the engine was really winding up, so low-speed torque pretty much sucked. His Boss Nine heads (which will fit on any 429-460 block) have holes just as large, but the advance in camshaft phasing and ignition technology “adjust” for these ancient and potential shortcomings. The same goes for the completely stock suspension. When the weak stuff breaks, they will amend the woe with stronger stuff.

No matter how careful I am with the throttle, and I’m talking Third and Fourth gear now, it literally wants to rip the tires off (laughs). Now that I’ve felt this thing, realistically, a 466-inch Boss Hemi would be about right for this car, but, as they say, anything worth doing is worth doing in excess.”

Can we get an AMEN!

’08 Ford Mustang
John Kaase Winder, GA
Vehicle weight w/driver: 3,800 pounds
Type: Ford displacing 589 cubic inches
(4.627 bore x 4.375 stroke)
Block: C&C MotorSports aluminum,
siamesed bores, iron liners, stock
10.32-inch deck height
Compression ratio: 10.5:1
Oiling: Moroso catalog pan, 7-quart, Kaase
oil pump
Rotating assembly: Sonny Bryant 4.375-inch forged crank,
6.800-inch Oliver steel I-beam rods,dished
Diamond pistons, Ackerly & Childs ring packs
Cylinder heads: Kaase Boss Nine, as-cast aluminum, 88cc
combustion chambers, Manley 2.30/1.90 valves,
Kaase/W.W. Engineering 1.75:1 rocker arms, Boss
Nine rocker covers
Camshaft: Comp Cams mechanical roller, .699-inch lift, 251/251
degrees duration at .050, 110-degree C/L, Trend 3/8-inch
pushrods, Ford Motorsport timing gear
Induction: Kaase Boss Nine intake manifold, Holley 1150 HP
carburetor, BSR Racing Products 16-inch air cleaner
(to clear Dominator and hood)
Power adder: are you kidding?
Ignition: Mallory distributor, MSD 6AL-2 box, 34 degrees
total timing
Exhaust: Chuck Lawrence built 2 1/8-inch primaries, 3.5-inch
collectors, Granatelli stainless 3-inch exhaust system
and mufflers
Fasteners: ARP
Output at flywheel: 902 hp at 6,800 rpm, 800 lb-ft at 5,100rpm
Built by: Jon Kaase Racing Engines, Inc.
Transmission: D&D Performance (2.66, 1.78, 1.30, 1.00, 0.80, 0.62:1)
T56 Viper-spec transmission, Quick Times steel bellhousing,
McLeod 11-inch twin-disc clutch, pressure plate, flywheel,
hydraulic throwout bearing
Driveshaft: Dynomax custom aluminum one-piece,
1350-series yokes
Rear axle: stock Ford 8.8-inch housing, clutch-type
differential, 3.31:1 ring-and-pinion
Front suspension: stock, MacPherson struts, lower control arms, antisway bar
Rear suspension: stock, coil springs, three-link, Panhard rod
Brakes: stock 12-inch disc, front; 12-inch disc, rear
Wheels & Tires
Wheels: American Muscle Black Magnum 500, 18×9, front; 18×10, rear
Tires: Pirelli PZero Rosso Asimmetrico, 255/45R18, front; 285/40R18, rear, Y-rated