Donald Farr
Former Editor, Mustang Monthly
January 1, 1998

1966 289 High-Performance Four-Speed

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Actual Rear Wheel: 144 hp/238 lb-ft

Estimated at Flywheel: 168 hp/278 lb-ft

Factory Rating: 271 hp/312 lb-ft

We felt Eugenia Hardaway’s four-speed 289 High-Performance K-GT would be a good comparison to Jeff’s automatic. But unfortunately, Eugenia’s hardtop--which she bought just a few months earlier--didn’t want to make power above 4,000 rpm. With smoke pouring out the twin GT exhaust trumpets, Paul first ruled out blow-by, then traced the potential problem to the carburetor. Carbmeister Mike Riemenschneider, on standby with his GT500KR, identified the four-barrel as an Autolite from a 1967 Thunderbird. In addition to being smaller than the stock 289 High-Performance Autolite, the carb was running way too rich, a condition that explained the black smoke and the car’s lack of horsepower at the top end. Although Eugenia’s four-speed K-GT produced a tad more rear-wheel horsepower than Jeff’s automatic K-GT, the manual soaked up less power, giving us only 168 hp at the flywheel compared to 176 net hp for the automatic.

1967 Shelby GT500 Four-Speed

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Actual Rear Wheel: 240 hp/354 lb-ft

Estimated at Flywheel: 281 hp/415 lb- ft

Factory Rating: 355 hp/420 lb-ft

In usual Shelby fashion, the 1967 GT500 was a case of Carroll Shelby one-upmanship over the Mustang. While the largest displacement engine available in the Mustang was the 390, Shelby transplanted the passenger car 428 into his GT500 and topped it with a pair of 600-cfm Holleys. From Shelby American, the GT500 was rated at 355 net hp.

For our Muscle Mustang Showdown, George Huisman, who operates Classic Design Concepts in Walled Lake, Michigan, trailered Cary Silver’s 1967 GT500 to Paul’s High Performance. "I told Cary I wanted to borrow his car," George explained, "and he said, ’Go ahead!’" As a former owner of the white-with-blue-stripes Shelby, George knew the car ran well a few years ago, but realized it spends more time in storage these days than on the road. "It probably hasn’t been driven 200 miles in the last 10 years," George said.

No problem. Cary's GT500 seemingly shook ground around the Dynojet on its way to a 240hp rear-wheel reading, which calculated to 281 hp at the flywheel, some 74 hp shy of Shelby's 355hp rating. The calculated flywheel torque, however, was amazingly close: 415 lb-ft at 2,800 rpm compared to Shelby's 420 lb-ft rating. Cary's GT500 was particularly impressive, considering George merely rolled the car off the trailer and onto the Dynojet rollers without touching a thing.