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Jon Kaase's Ford Mustang Short Block Engine - Horsepower!


Photography by Ed Taylor

589CI, 885HP, Kaase Boss Ford
Jon Kaase Racing Engines, Winder, GA

If there were a Ford engine builder's hall of fame, you would find Jon Kaase's name (pronounced kah-zee) somewhere near the top of those who fiddle with carburetors and gasoline. While Kaase's reputation is still growing within the street performance arena, he's been building and tuning competitive Ford drag race engines for more than 30 years. Lately, he's gained considerable notoriety for winning the Engine Masters' competition three times (once with a Pontiac), which brings us to the present and his latest venture into resurrecting Ford's performance heritage. Kaase is using the Boss Nine moniker to refer to the remake of the original Shotgun Boss 429 head. We're talking a large-by-huge oval intake port head Kaase says is capable of 1,000 normally aspirated horsepower. This 589ci engine made 973 hp and 800 lb-ft with a more aggressive camshaft, but Kaase deemed it too rough for his street taste. The engine is bolted into a virtually new '07 Mustang, and as you can see, this new/old Boss offers more clearance. The engine also fits under the stock Mustang hood with no scoop or bubble required. How's that for a sleeper? Kaase estimates the Mustang is capable of a 200-mph top end charge with its Viper-spec six-speed. Car Craft is assembling a slightly smaller version of this engine to test one of the first sets of production heads, so there's more meat on this beast. But we thought you'd like a quick shot here of what Kaase's been whittling on inside his Georgia skunkworks.

A: Trans
Kaase determined that an automatic would be wimpy, so instead he spec'd a Tremec T56 Viper-spec six-speed bolted to a Quick Time bellhousing that houses a McLeod twin-disc clutch system. Imagine how little throttle it takes to move the car in First gear with just a touch of the gas pedal when your engine is making in excess of 630 lb-ft at 2,500 rpm.

B: The Car
Let's talk plain black wrapper, shall we? The car is a simple '07 Mustang with a set of 18x10-inch American Muscle five-spoke wheels in the back. Other than perhaps a distinctive rumble out the exhaust, Kaase's sleeper should seem like just a generic Mustang. Now you know.

C: Heads
This is where it all happens. Kaase built these heads to retrofit onto any production or aftermarket 429/460 Ford block. They are semihemispherical, which really means they're more wedge than Hemi. The Boss Nines feature 2.300/1.900-inch valves but do require specific shaft rockers. These heads are fitted with W. W. Engineering 1.75:1 rockers and Manley springs. The exhaust rockers are reminiscent of Hemi pieces with their exceptionally long arm length. If you have a set of production Boss 429 valve covers, they will bolt on, but Kaase has also designed his own Boss Nine covers that look very similar.

D: Intake
The Kaase heads will also require a Kaase-built single-plane intake like this one that mounts a CFM-built 1050 Dominator fuel mixer. The motor sits low enough in the chassis that with a 3x16-inch-diameter air cleaner (to clear the longer Dominator bowls), everything squeezes under the stock hood without a scoop or bubble to give away what's under it.

E: Exhaust
Chuck Lawrence built the 2 1/8-inch primary diameter headers with a 3 1/2-inch collector leading to a complete Granatelli 2 1/2-inch exhaust system that you can't see in this photo--but trust us, they're effective.

F: Accessory Drive
That's a Billet Specialties serpentine accessory drive on the front of this monster, complete with a new alternator and power steering pump. Even the A/C still works.

G: Short-Block
Kaase traded for the aluminum race block that ended up with a massive 4.627-inch bore followed by a 4.375-inch-stroke Sonny Bryant steel crank. This 589-incher swings 6.800-inch steel Oliver rods and 10.5:1 pump gas-friendly Diamond pistons. The current cam is a mild Comp roller with 251/251 degrees of duration at 0.050-inch tappet lift pushing the net lift up to 0.660 inch. A trimmed Moroso oil pan clears the Mustang's rack-and-pinion steering.

2,600 644 319
3,000 596 340
3,500 714 476
4,000 753 573
4,500 794 681
5,000 794 756
5,300 801 794
5,500 780 817
6,000 757 864
6,400 715 885
6,500 715 885
7,000 648 864

There is actually more valve cover and spark plug access in Kaase's '07 Mustang than in original Boss 429 engines in the '69 Mustang.

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