What was the standard engine displacement in the 1965 Ford Mustang GT?

The standard engine displacement in the 1965 Ford Mustang GT was 289 cubic inches. In this context, “standard” refers to the engine required for the GT Equipment Package, not the base engine available in every Mustang.

Ford introduced the Mustang GT Equipment Package in April 1965. It was available only with a V8, and the ordinary GT used the 225-horsepower, four-barrel 289-cubic-inch V8. Buyers could also choose the high-performance K-code 289, rated at 271 horsepower, so the GT badge did not mean every car had identical engine output.

The package added functional hardware and visual identification: front disc brakes, quicker steering, special handling components, dual exhaust, fog lamps, rocker-panel stripes, and extra instrumentation. That makes 302, 351, and 427 common mix-ups: those displacements belong to later Mustangs or other Ford performance applications, while the 302 did not replace the 289 in the Mustang lineup until the 1968 model year. The GT was an equipment package, not a separate body style.