Shelby fitted the C6ME ‘Police Interceptor’ 428 into the mustang which created the GT500. It also included a host of other upgrades including Holley BJ/BK carburetors, manifolds, RUGS-1 transmission, 3.50 Traction-Lok rear end, braking system with KH calipers and drums, a louvered hood, inboard driving lights, optional 10-spoke wheels with Goodyear tires.
The GT500 arrived for 1967 and was an altogether different animal than the Shelby GT350. The biggest change was the engine. It was powered by a monster 428 CID engine with two 600-CFM Holley carburetors, rated at 355 hp and 420 lb-ft of torque, paired with a choice of a four-speed manual or a three-speed automatic. The engine itself also featured a cast aluminum intake manifold. Actually, there were two engine options for the GT500 for 1967 — the other was Ford’s 427 CID V8.
For 1967, Ford offered the Mustang with their tried-and-true 390 V8 in the GT350. It had a bore and stroke of 4.05 x 3. 78 inches. To make Shelbys compete in road-racing and acceding to demands from Shelby’s audience, they were given room for big-block power. That is how Shelby got the reworked 428-cid “Police Interceptor” stuffed it into the Shelby. The engine was good for ~355 hp to 360 hp and 420 lb-ft of torque.
A bigger engine wasn’t the only mechanical change: Shelby fitted stiffer front springs to Ford’s stock suspension, an upgraded anti-roll bar and Gabriel shock absorbers. The GT500 also featured front disc brakes as standard equipment, which would come in useful for a lot of owners.
In the cockpit the GT500 also received an upgraded 140-mph speedometer, an 8,000-rpm tach and a couple of other additional gauges. But the biggest and the most noticeable change, and also one of the most practical, safety-wise, was the roll bar. Badging was relatively light on the inside: Cobras appeared on the passenger-side dash as well as the three-spoke steering wheel trimmed in wood. There were plenty of other opportunities to advertise the car’s performance on the outside, with Cobra badging along with a rocker stripe. Buyers had three options when it came to wheels, and all were 15 inches in diameter — this was in the age of smaller wheels.
The GT 500 is not a racing car, although but for a few subtle differences its engine is the same as the one that propelled Shelby’s Fords to victory at Le Mans. Seven liters in a Mustang! The early GT 500 engineering prototype was the fastest car ever to lap Ford’s twisty handling loop, except for the GT 40s, of course. And the same car cut a quarter-mile in 13.6 seconds at 106 mph. Super car!