1967 Shelby GT500 427 Side Oiler

Every 1967 Shelby GT500 that left the factory carried a 428, not a 427. So when a GT500 shows up with a genuine side-oiler under the hood, the first question is whether you are looking at a very good engine swap or something considerably rarer. There is exactly one factory answer to that question, and its story involves a test track, a set of tires, and a car Ford was afraid to sell.

There is a detail about the 1967 Shelby GT500 that trips up nearly everyone who has not gone looking for it. Ford built roughly two thousand of them that year, and not a single one left the production line with a 427 under the hood. So when a 1967 GT500 turns up wearing a genuine side-oiler, you are looking at one of two things: a very well-executed engine swap performed at some point in the past half century, or something so rare that only one example has ever legitimately existed. The story behind that single car involves Carroll Shelby, a Goodyear test program, a stretch of Texas asphalt, and a decision Ford made because it was frightened of what it had built.

The Engine That Was Not Supposed to Be There

Start with why a 427 in a 1967 Shelby is so jarring to anyone who knows these cars. Ford’s FE engine family included both the 428 and the 427, and although they share external dimensions and a family name, they were built for completely different lives. The 428 was a passenger-car engine, cast conventionally, designed for torque and durability at moderate engine speeds, and cheap enough to put in something a dealer had to warranty. The 427 was a racing engine that happened to be sold to the public in limited numbers, expensive to build and expensive to keep alive. Ford’s product planners were never going to sign off on putting the second one into a car aimed at people who wanted a fast Mustang for the street.

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What Ford Actually Shipped in 1967

The standard 1967 GT500 engine was the 428 Police Interceptor, a big-bore FE-family V8 fitted with an aluminum medium-riser intake carrying two Holley four-barrel carburetors and rated at 355 horsepower. That rating was almost comically conservative, chosen with one eye on insurance underwriters rather than on the dynamometer. Real output was well above 400. Ford produced 2,048 GT500s for 1967 alongside roughly 1,175 of the small-block GT350 – a combined 3,225 Shelbys for the year – and the GT500 outsold its lighter sibling by nearly two to one, which tells you exactly what the market wanted by that point in the decade.

Side-Oiler Versus FE: The Difference Under the Valve Covers

The 427 side-oiler is a different animal from the 428 despite sharing the FE family designation. Its defining feature is the revised oiling circuit cast into the left side of the block, which feeds the main bearings before routing oil to the top end rather than the other way around. That single change made the engine survivable at sustained high rpm, which is why it powered the GT40s at Le Mans and dominated NASCAR. It was also a cross-bolted, thin-wall-cast, expensive racing engine, entirely unsuited to a car a dealer had to warranty for a customer who would drive it to work.

The Super Snake and the Tire That Ended It

Which brings us to the Super Snake. In 1967 Goodyear needed a high-speed tire endurance demonstration and Shelby supplied a GT500 fitted with a genuine 427 racing engine, reportedly making somewhere around 520 horsepower. The car ran for hours at sustained speed at Goodyear’s San Angelo test facility, averaging well over 140 miles per hour, and the tires survived. Shelby then proposed a production run. The problem was cost: the finished car needed to sell for roughly double a standard GT500, and the dealer network concluded nobody would pay it. Exactly one Super Snake was built, and it remains one of the most valuable Mustangs in existence.

Why the 1967 Car Looks Nothing Like a 1966

Visually the 1967 Shelby broke sharply from the 1965 and 1966 cars, and that change was structural rather than cosmetic. Ford’s Mustang had grown for 1967 to accommodate big-block engines, gaining width and mass, and Shelby’s team responded with a fiberglass nose extending the front end roughly three inches, a fiberglass decklid with an integrated spoiler, functional brake ducts, and rear quarter scoops. The high-mounted driving lamps in the grille became a signature, though some states forced Shelby to move them apart because of headlight spacing regulations. It is a far more theatrical car than the stripped, race-derived 1965 GT350.

The Swap That Everybody Eventually Considers

The 427 swap has genuine appeal for owners who understand what they are taking on. The side-oiler shares FE external dimensions with the 428, so it drops into the engine bay without fabrication, and the payoff in top-end capability is substantial. The costs are equally real: side-oiler blocks and correct components are extraordinarily expensive, the engine wants regular attention, and its torque delivery is peakier than the 428’s, which makes the car less pleasant on the street. Owners who make the change generally keep the original 428 crated in the corner of the garage, and they are right to.

Authenticating a GT500 Before You Write the Check

Authenticating a 1967 Shelby means going well past the badges. Every genuine car has a Shelby American serial number on the plate riveted to the driver’s inner fender apron, in addition to the Ford VIN, and the Shelby American Automobile Club registry can confirm whether that number and the car’s documented history line up. Fiberglass panels, correct Shelby-specific interior components, and the roll bar with its inertia-reel harnesses are all reproduced today, so appearance proves nothing. The registry entry and the fender apron plate are what the market actually transacts on.

The Most Interesting Shelby Nobody Could Buy

What makes this particular chapter compelling is that the most interesting version of the car was the one Ford would not let anyone have. The Super Snake proved the concept comprehensively, survived a punishing endurance run, and then died on a spreadsheet because the price was roughly double what the dealer body thought the market would bear. Every 427-powered 1967 GT500 built since has been somebody privately finishing the job Shelby started and the accountants stopped. It is a rare case where the aftermarket is not modifying a car away from its intended form but rather completing a version the factory had already built once, tested thoroughly, and then declined to sell. Share your thoughts in the comments below.

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