The K-Code Guide
What Is a K-Code Mustang?
A K-code Mustang is a 1965, 1966 or 1967 Ford Mustang that left the factory with the 289 cubic-inch High Performance V8 — Ford's 271-horsepower “HiPo”, the top engine of the 1965 and 1966 Mustang. The name comes from the engine code: the letter K in the fifth position of the car's VIN.
About 13,200 were built across the three model years. Nobody knows exactly how many survive; the registry works with an estimate of 2,000 to 4,000.
Where does the K come from?
Every 1965–67 Mustang carries an 11-character VIN, and its fifth character is the engine code. On these cars, a K means the 289 High Performance. The first five characters are shared by every K-code of the same year, plant and body style — which is why the public registry listing shows them and masks most of the unit number.
| Position | Meaning | On a K-code |
|---|---|---|
| 1 | Model year | 5 = 1965 (including the early “1964½” cars) · 6 = 1966 · 7 = 1967 |
| 2 | Assembly plant | F = Dearborn, Michigan · R = San Jose, California · T = Metuchen, New Jersey |
| 3–4 | Body serial code | 1965–66: 07 hardtop · 08 convertible · 09 fastback — 1967: 01 hardtop · 02 fastback · 03 convertible |
| 5 | Engine code | K = 289 cu in four-barrel High Performance V8 |
| 6–11 | Consecutive unit number | Six digits, counted per assembly plant |
Have a number in front of you? Decode it — it explains each character as you type.
What made the 289 High Performance different?
The HiPo was Ford's small-block built to rev. It shared its displacement with the regular 289s, but the valvetrain and bottom end were reinforced so the engine could live near 6,000 rpm, and the car around it got the parts to match.
- Displacement
- 289 cu in (4.7 L) V8
- Output (gross)
- 271 hp at 6,000 rpm · 312 lb-ft at 3,400 rpm
- Compression
- 10.5 : 1
- Valvetrain
- Solid (mechanical) lifters, screw-in rocker studs, stiffer valve springs
- Induction
- Autolite 4100 four-barrel carburetor
- Ignition
- Dual-point distributor with centrifugal advance only
- Bottom end
- Connecting rods with 3/8-inch bolts (5/16 on a standard 289), a wider, heavier harmonic balancer
- Exhaust
- Free-flowing cast-iron manifolds
Drivetrain
- Transmission
- Four-speed close-ratio Toploader; a C4 automatic from 1966
- Rear axle
- Ford 9-inch — other 1965–66 V8 Mustangs had the 8-inch
How many K-code Mustangs were built?
About 13,200 over three model years, with a steep drop at the end: the 1967 Mustang offered a 390 big-block, and the HiPo became a rare order.
| Model year | K-codes built |
|---|---|
| 1965 (incl. 1964½) | 7,273 |
| 1966 | 5,469 |
| 1967 | 489 |
| Total | 13,231 |
Ford's own build records for 1965–66 do not survive. Those two figures come from Tony Gregory's research, the 1967 figure from Marti Auto Works' Ford production data (older sources give 472). A 1976 Ford Parts & Service letter puts 1965 at 7,026 — read every figure as close, not exact.
How many survive is an estimate — 2,000 to 4,000 is the figure the registry works with. 130 of them are documented here so far, each one turning part of that estimate into a count.
Which Mustangs could be ordered as a K-code?
All three body styles — hardtop, fastback and convertible — in all three model years. The option arrived in June 1964, a few weeks after the Mustang's launch, so some of the early cars known as “1964½” (titled as 1965 models) are K-codes too.
In 1965 the HiPo came only with the four-speed and the Special Handling Package; from 1966 a C4 automatic could be ordered as well. After the 1967 model year the 289 High Performance was gone from the Mustang.
Is a Shelby GT350 a K-code?
The 1965 and 1966 GT350s — the ones this registry covers — all started life as K-code Mustangs from Ford's San Jose plant, and Shelby American reworked the engine to 306 hp. A GT350's legal identity, though, is its Shelby serial — SFM5S… for 1965, SFM6S… for 1966 — and authentication is the domain of the Shelby American Automobile Club, which holds the factory records. GT350s are listed in this registry; they are not verified here.
How do you tell a real K-code?
The K in the VIN is where the check starts, not where it ends. On an original car the same identity shows up in four places, and they agree with each other:
- Fender apron
- The VIN is stamped into the driver's-side front inner fender apron, visible with the hood open.
- Warranty plate
- The plate on the driver's door carries the VIN again, with the body, color, trim, build date, sales district, axle and transmission codes.
- Engine block
- A K-code block normally carries the car's full VIN, stamped on the passenger side near the front, plus a casting number — C5AE-6015-E on nearly all of them — and a casting date code such as 5D20 (April 20, 1965).
- Transmission
- The HiPo Toploader has an ID tag — HEH-S, HEH-T or HEH-BX, RUG-N from the 1967 model year — a casting date and, on most cars, the VIN stamped into the case.
A single K on a single plate proves little — plates can be swapped and numbers restamped. What convinces is agreement: the stamps, the plate and the date codes all telling the same story as the car's build date. Not every car was stamped everywhere, and a service replacement block never is; a replacement engine does not make a car less of a K-code, because the identity lives in the body. Comparing all of it is what an Admin Verified listing in this registry documents — a plausibility check on the evidence, not a legal certificate of authenticity.
Sources
- Tony Gregory, The 289 High Performance Mustang, 4th ed. (2006) — production 1965–66
- Marti Auto Works — Ford production data from 1967
- eKschange — “K codes by the numbers”
- eKschange — “List of HiPo differences over the standard 289”
- eKschange — “HiPo VIN stamp”
- Hagerty — 25 Greatest Mustangs: 1965 Hi-Po 289
- Hagerty Learning Garage — 1964½ Ford Mustang
- Shelby American Collection — 1965 Shelby GT350
Last reviewed . Something wrong or missing? Tell us.
Own a K-code Mustang?
Registering is free. Every car documented here makes the record more complete.