1964-1973 Mustang Engine Codes

The first generation of Mustang launched halfway through April of 1964 and even by 1965 there were significant differences in the engines that were available. For instance, even though you could get a six-cylinder engine in 1964 or 1965, they were two very different engines, with different displacements, horsepower and torque ratings, and hardware.

It’s easier to reference the “engine codes” when trying to establish details about any of the first-generation Mustang’s engine options. Each engine was tied to a unique single letter code that was part of the VIN on the Mustang’s data plate. Using a Classic Mustang data plate decoder, you can learn a lot about your Mustang’s original options.

Because the codes were a single letter, they did get reused, so it’s important to reference both the year and the letter in order to establish what type of original engine your Mustang had.

Engine Options

Most years had at least four options: A six-cylinder that served as the base, a four-barrel carburetor V8, a two-barrel carburetor V8, or a high-performance four-barrel carburetor V8. Many of the packages that we consider especially collectible now, like the California Special or GT package, required one of the two V8s that came with a four-barrel carburetor installed.

Some engines were only available for a single year, this was partially because Ford was in the middle of some large changes and partially because if an option wasn’t particularly popular it got pulled before the next year. New car sales were significantly more focused on customization and options than they are today, and subsequently the engine options expanded to keep up with customer demands and special editions.

If you want to find out what paint colors came stock for each classic Mustang year, check out our classic Mustang engine paint guide.

Engine Families

Thriftpower

The inline-six that served as the base engine option grew in size throughout the first-generation, gradually growing from a 170 CID inline-six offered in 1964 to a base 250 CID offered by 1969. The 250 CID remained in production through 1980. Frequently referred to as “Thriftpower Six” engines, these six-cylinders were intended to offer performance with fuel efficiency.

Windsor vs Cleveland

Ford’s small block V8s hit an important divide during the first generation of Mustang. The Windsor and Cleveland small block V8s are named after the plants that they were manufactured in. Though they frequently were produced concurrently and with identical displacements, these two small-block V8s were far from identical.

The Clevelands were associated with higher-performance functions. This was due to cylinder heads that encouraged better flow and a much-improved crankshaft.

The Windsor was significantly lighter and easier to work on since it didn’t use a block-incorporated timing chain like the Cleveland.

The Boss 302 engine is one of the most unique examples in the Windsor/Cleveland dichotomy since it used a lighter Windsor block but had Cleveland cylinder heads bolted on, which improved breathing.

Big Block V8 vs Small Block V8s

Though the Ford Mustang didn’t launch with any big block V8s, throughout the years there were multiple big block options. The first of these was the “S” code Thunderbird special. Though this engine was very powerful, it had a relatively short run since Ford moved on to engines with even larger displacements.

Most of the engines offered in the first generation Mustang’s extensive roster were small block V8s. Though you can usually make an educated guess as to whether or not an engine is a small or large block V8 based on its displacement, this isn’t always accurate. Big Block engines are certainly larger, but they’re also more “Y” shaped, which affects the bore to stroke ratio.

Check out our article for the differences between big and small-block V8s for a complete inventory of the ways you can tell a big and small block apart, and why one may be better for your intended purposes.

Engine Code U

170 CID Inline Six 101 hp

The U-code engine was only produced for 1964. This inline-six cylinder engine was actually originally used on the Ford Falcon, but was borrowed for the first half-generation of Mustang. It was replaced in early 1965 by a different inline six.

If you have a U-code Mustang, you might feel a little bummed out. This was one of the least powerful engines in the early Mustangs, but it’s actually a very exciting find. A U code means that you have one of the very first Mustangs produced. The U-code engine was replaced in July, so U-code Mustangs could have only been produced in the first three months of the Mustang’s life. Though Ford stopped using this particular engine on the Mustang very early into production, they continued to produce this inline six (a Thriftmaster) through 1972.

This means that replacement parts aren’t too difficult to find, though if you’re digging through a junkyard you may be better served checking under the hood of an Econoline van or Ford Bronco. Both of these vehicles were equipped with the same engine, but they received a few heavy-duty upgrades to account for the larger size of the vehicles.

Engine Code F

260 CID V8 164 hp

Though the “F” code designation was used later, the first F-code engine was only for the 1964 Mustang. Borrowed from the Ford Fairlane, this small-block V8 is an example of Ford’s Windsor series. A well-regarded V8, this model of Windsor could also be found in the Ford Falcon and the Mercury Comet.

Though Windsor model V8s remained in production for the entirety of the first-generation of Mustang, this particular unit stopped being manufactured after 1964. It was only in production for two years, and though used in several popular models, only a little over 600,000 of these engines were ever made across all production.

Engine Code D

289 CID V8 210 hp

The D code engine is perhaps the rarest of all from the Mustang’s 1964 production year. The D-code was meant to be a kind of intermediate engine. For people who wanted a V8 with a four-barrel carburetor but who didn’t want to splurge for the high-performance K-code, the D-code was a kind of compromise. Though it had the same displacement as the K-code engine, and it also was equipped with a four-barrel carburetor, the D-code engine produced less horsepower.

One major benefit to the D-code engine over its higher-performance relative is that the D-code’s lower compression ratio meant that it uses regular fuel rather than premium. This was not true of many of the other intermediate V8s produced during the first generation of Mustang.

Engine Code K

289 CID “HiPo” 271 hp

The “K-code” engine was the high-performance option for the first years of the Mustang. Sometimes just referred to as “HiPo,” this engine was considered very desirable. Though the bore, stroke, and displacement are all identical to other Ford small-block V8 engines, the performance is improved thanks to differences in cam timing, improved carburetor, and more.

The K-code engine came with a lot of other performance goodies designed to help it achieve its promised high-performance without mechanical failure.

Because of all of the additional improvements that were necessary for the K-code Mustang, it was a very expensive option, which affected its popularity considerably. A version of this engine can be found in the Shelby GT350, but otherwise only about 25,000 K-codes were made before 1967 when the engine was no longer offered.

Engine Code T

200 CID Inline-Six 120 hp

The T-code engine replaced the U-code as the base engine option, and due to its long run is one of the most abundant engines produced. Starting in 1965, this engine was used in the Mustang through 1971. A version of this engine was reintroduced to the Mustang in 1979, and that version is especially sought after.

If you have a T-code first-generation Mustang, there’s no reason that you couldn’t upgrade to the one produced for the Fox Body Mustang. The major difference between the two is the bell-housing shape and the location of the starter. This version is sometimes referred to as a “Big Bell 200” engine. For the engines manufactured between 1968-1969, the horsepower inexplicably dropped to 115 hp.

Engine Code C

289 CID V8 200 hp

In 1965, the C-code engine replaced the F-code engine from 1964 as the base V8 engine. Like the F-code, this engine has a two-barrel carburetor, but it also has a larger displacement which contributes to its improved horsepower and torque.

Like the V8s from 1964, the C-code engine is a Windsor small-block V8.

For 1968, the last year it was manufactured, the C-code dropped to 195 hp and 288 lb-ft. This is one of the most abundant classic Mustang engine codes since a lot of individuals were interested in having a V8 but didn’t want to pay for the upgrades to the higher performance V8s.

Engine Code A

289 CID V8 225 hp

The A-code engine replaced the D-code engine from 1964 as the “compromise” V8. A significant step up from the base-V8, the A-code engine offered a four-barrel carburetor but was still less expensive than the “HiPo” K-code engine.

Unlike the D-code engine however, the A-code engine had a slightly higher compression ratio which made premium fuel a necessity. The higher compression ratio also translated into more horsepower.

Engine Code S

390 CID Thunderbird Special V8

The S-code engine was introduced in 1967 as an alternative for people who wanted even more power than the HiPo K-code engine was capable of producing. While as all of the other V8s that had been offered up till this time were small-block, the S-code engine was the first big-block V8 engine for a Mustang.

Though these engines came standard with a cast iron intake manifold, many actually came with an alternative aluminum intake manifold that was intended to be a dealer-installed option. When equipped with the aluminum intake manifold, the horsepower improved significantly.

Though not as impressive as later big-block V8s, this engine was a jaw dropper at the time, and just having it as an option necessitated changes to the overall dimensions of the Ford Mustang. The size had to be increased in order to allow enough space for a big V8. It’s for this reason that Mustangs produced after 1967 tend to be better candidates for modern V8 swaps, like Coyote swaps.

Engine Code F (not the same as before)

302 CID V8 210 hp

The F-code engine replaced the 289 CID V8 that had served as the base V8 engine on Mustangs up until this time. The improved displacement reduced the distance between the base V8 and the next step up.

Manufacturers changed from gross to net horsepower and torque ratings in 1972. When this happened, the horsepower dropped to 140 hp @ 4,000 RPM and 239 lb-ft @ 2,000 RPM despite no substantive differences between the 1971 and 1972 models.

Engine Code J

302 CID V8 230 hp

J-code engines were designed to replace the previous “compromise” V8s, but with more V8 options available, it was starting to seem like less of a good deal.

These engines had the same CID as the base V8, but an improved four-barrel carburetor and a few other minor improvements. Overall, the J-code was only in production for a year and subsequently is exceptionally rare, if not particularly highly valued.

Engine Code R

428 CID Cobra Jet 335 hp

The “R” code engines were intended to be drag racers. In addition to their big-block V8 displacement and power, the R-code engine also had a Holley-4 barrel carburetor and a ram air hood that was functional.

The R-code Mustang was very rare and is highly valued and sought after. Only 1,300 of these were made (not counting Shelby Mustangs). An R-code Mustang in good condition can easily sell for over $160,000, and it’s almost impossible to find one unless you’re looking on a premium classic car site.

Engine Code W

427 CID V8 390 hp

There are no accounts of any Mustangs actually being produced with this engine, but it was offered very briefly before being replaced with the Cobra Jet. It was a very popular engine for Mustangs in drag racing. This big-block V8 was immensely powerful, but after 1968 the Mustang had a long list of powerful V8s and many of them were attached to highly desirable packages.

Engine Code X

390 CID V8 280 hp

The X-code engine was only offered for a single year, 1968. It is considered one of the rarest engine options.

In total, 733 Mustangs were manufactured with an X-code engine. 477 of those were hardtops, 189 were fastbacks, and 67 were convertibles.

Engine Code G

302 CID Boss 302 290 hp

For the Boss 302, two Ford small-block V8 engines were combined, giving the vehicle the best aspects of both. From the Windsor, the Boss 302 got a small and light block, but from the Cleveland, it received its easy-breathing cylinder heads.

The small size and light overall build of the Boss 302 made it a fast car that could carve corners, unlike its more robust Boss 429 sibling which was a drag monster.

Engine Code H

351 CID Cleveland V8 250 hp

The H-code engine was a Cleveland 351 engine that was used in a variety of Ford vehicles. The Cleveland is often compared to the Windsor, its predecessor. Both are small-block V8 Ford engines, but the Cleveland is larger and heavier. Though some of this size difference was due to developments like integrated timing chain housing, most of it was due to an all cast-iron design. The cast-iron design makes the Cleveland significantly sturdier.

Engine Code L

250 CID I6 155 hp

When first introduced, this six-cylinder engine was offered not as a replacement for, but in addition to the existing six-cylinder engine at the time. Starting in 1971, the L-code engine became the new base model engine for the Ford Mustang. It remained in production through 1980 in other non-Mustang vehicles.

A two-barrel carburetor version of this particular inline-six engine became an incredibly popular racing engine in Australia.

Engine Code M

351 CID Cleveland V8 290 hp

The M-code engine was used in the 1969 Shelby GT350, the Mach 1, and a handful of other Mustangs made during this time. Not to be confused with the Windsor small-block V8 that has an identical displacement, the M-code is actually one of the first examples of the Cleveland engine style.

By using larger valves and stiffer valve springs, the M-code was able to offer higher compression and higher performance than most of the Cleveland 351s.

Engine Code Q

428 CID V8 335 hp

The Q-code engine was essentially the version of the Cobra Jet engine that didn’t come with a functional hood scoop. Though frequently sold with a dummy hood scoop, the “R” designation one came with a true Ram Air scoop.

The lack of a hood scoop didn’t impact the power output though, and in every other way the Q-code engine is identical to its better known R-code Cobra Jet cousin.

Engine Code Z

429 CID Boss 429 375 hp

The Z engine code was designed for the Boss 429 and was also used in some Nascar and other racing applications. One of the easiest checks to see if you’re looking at one of the very few existing Boss 429 Mustangs is to look at the data plate and see if it has a Z code.

The Z-code engine on its own is desirable. The connecting rods and the crankshaft were both made out of forged steel. The carburetor is rated at 735 CFM, and was mounted on an aluminum high-rise intake manifold that made sure that this engine could breathe. It needed to! Though not all of the Boss 429 Mustangs made it to the track, enough did that the vehicle was able to establish itself as a drag beast.

Though listed at 375 horsepower, the actual output of this engine is highly disputed. It’s likely that it was curbed down in order to reduce the insurance costs.

Engine Code R

351 CID V8 330/275 hp

In 1971, the Boss 302 and Boss 429 were replaced by the Boss 351. The engine that powered the 351 was a high-output Cleveland V8. The cylinder heads were almost identical to the Boss 302’s and flowed just as well. Unlike the Boss 302, the Boss 351 featured a solid-lifter cam with an aggressive profile.

The Boss 351 was only available for a single year. During that year, it got rave reviews for its power and speed. Though the engine returned in 1972, it was definitely changed.

The cylinder heads, pistons, and camshafts were different in the 1972 R-code engine. This resulted in a detuned version of the Boss 351’s engine.

Engine Code Q

351 CID V8 266 hp

The second Q code was introduced in 1972. Though it was a Cleveland-style V8 with a 4-barrel carburetor, it wasn’t the same as the first Q-code engine. This one was less powerful.

Though this engine wasn’t advertised as a Cobra Jet, that is how it’s referred to in shop manuals.

First Generation Mustang Engines

Whether you plan to do a full restoration or are considering upgrading your existing Mustang parts, knowing what your vehicle came stock with is an important first step of the process. While it’s easy to reduce the engine component to displacement, the differences between each engine were significantly more nuanced than that, and is why some pieces aren’t interchangeable.

Once you understand your engine’s family and construction, you’ll be in a much better position to modify or restore it using the appropriate first generation Mustang engine parts.