Today, some 46 years later, the K-code "Hi-Po" Mustang is still one of the most sought after classic Mustangs. With just three years of production and something less than 13,000 produced, the K-code certainly has higher numbers than, say, a Shelby Mustang. But when you consider the overall production numbers of the '65-'67 Mustang, the K-code represents barely one percent of production. That's what makes the K-code rare.
The block's casting number...
The block's casting number is found on the passenger side of the block above the starter mounting area. All '65-'67 289 blocks, including the Hi-Po versions, used C5AE-6015-E (or C4OE-6015-F for '64-1/2). This number alone does not make a 289 a Hi-Po; it just makes it a six-bolt 289 block cast after July of 1964 (or a five-bolt for June and July 1964).
The K-code option has had many stories written about it over the years, most based on accurate information, but there have been some discrepancies over the years as information is gathered from various places. It doesn't help that, like most Mustang production information, Ford often made assembly line changes during production shifts just to keep the assembly line moving. Thankfully, the K-code engine itself, built at Ford's Cleveland Engine Plant No. 1 in Brooke Park, Ohio (now home to Ford's EcoBoost V-6 engine), had very few production changes.
With the help of Bob Mannel, author of Mustang & Ford Small Block V8-1962-1969, we've delved deep into Bob's book, original Ford literature, archive photos, and even tore apart a K-code engine ourselves locally that was in need of a rebuild. Along the way, we learned plenty of K-code details and have a new-found appreciation for the performance small-block that Ford initially offered in the '63 Fairlane and eventually installed in Mustangs, as well as the Shelby 289 Cobra, G.T. 350, and several other vehicles. We hope this inside look at the Mustang's K-code 289 Hi-Po engine answers your questions, helps you find that K-code Mustang you're looking for, or assists you in building an accurate Hi-Po 289 for your restoration project.
As noted in the text, Hi-Po...
As noted in the text, Hi-Po Mustangs generally had their VIN stamped into the block. These Mustangs were the only '65-'67 Mustangs to have their VIN stamped into the block and it can be found on the passenger side front above the oil pan rail.
We'll start with the foundation for every 289 Hi-Po: the engine block. Let's get one thing out of the way right at the start--the Hi-Po block was NOT a special high-nickel block or cast just for Hi-Po builds. The Hi-Po block started life at the same foundry with the same casting numbers as regular 289 D-, C-, and A-code blocks. While there are earlier Hi-Po casting numbers, the one to concern yourself with for '65-'67 Mustangs is C5AE-6015-E (and C4OE-6015-F for '64-1/2). What made the Hi-Po block different was how Ford inspected blocks for Hi-Po use. Ford used a special dye to inspect the block for minute cracks and imperfections. Essentially, Ford used "perfect" 289 blocks as the starting point for the Hi-Po and then added the coveted larger heavy-duty main caps for strength.
Most, but not all, Hi-Po 289...
Most, but not all, Hi-Po 289 blocks got the
This photo provided by Bob...
This photo provided by Bob Mannel shows a prototype 289 Hi-Po block. As you can plainly see, the 1/2-inch oil gallery plugs are standard press-fit plugs, just like all the other 289s built at the Cleveland plant. Carroll Shelby upgraded his Hi-Po engines to screw-in gallery plugs during
The Hi-Po main cap is a stout...
The Hi-Po main cap is a stout piece and easy to spot. The main cap is a full 15/16-inch thick and does not taper at the top like the standard 289/302 main cap. Hi-Po caps will generally have a C3 casting on the number 5 cap. (Look-alike Mexican 302 caps will have casting date codes.) If you can find the caps, all you need to do to add these to your 289 build is to have the mains line-bored.
Other misnomers through the years include screw-in oil gallery plugs (a few early '63 blocks had them but it was Shelby that added them during his blueprinting for Cobra and Daytona Coupe use that started this rumor). Standard 289 blocks, including the Hi-Po, had standard 1/2-inch press fit plugs. Hi-Pos did not have screw-in core plugs either. As a matter of fact, the block had no discerning outward differences except that most had the vehicle's VIN stamped in the side of the block (regular 289s did not) and the often used "HP" designation in paint inside the bellhousing area, though not every Hi-Po block got this marking.