For 43 years, the 289 High Performance small-block has been more myth than fact. It probably gets more credit with enthusiasts than it deserves due to rarity more than anything. What makes it "high-performance" isn't unusual or rare. What Ford did to the 289 isn't any more out of the ordinary than good, old-fashioned, hot-rodding trickery.
The 289 High Performance is a warmed-up 289 with a hotter solid-lifter camshaft, cylinder heads and a dual-point ignition designed for higher revs, cast-iron header exhaust manifolds, and a wider harmonic balancer.
So what's the big deal? Not much, unless you're restoring a K-engine-code '65-'67 Mustang or are interested in building an authentic 289 Hi-Po small-block for your non-K-code Mustang. What makes the Hi-Po a big deal is authenticity when building a K-code Mustang with the real thing between the shock towers.
We're going to teach you the basics of the 289 High Performance with quick facts you can use in your engine building and Mustang spotting. Based on what we know about the Hi-Po, you can build a homegrown Hi-Po engine without spending a fortune in elusive castings and pieces. You can achieve the clatter of 16 mechanical tappets and the throaty tailpipe sound with the right camshaft and exhaust tuning. And, you can generate more horsepower and torque without suffering with driveability issues.
From the factory, the '65-'67...
From the factory, the '65-'67 Mustang's 289 High Performance was equipped with chrome valve covers and an open-element air-filter assembly.
Although the 289 High Performance block has a unique part number, it was not a unique block. The only difference was its wider main bearing caps. According to the 289 High Performance Mustang book by Tony Gregory, the 289 2V and 4V engines have 151/416-inch main caps that taper to 51/48 inch at the top. The Hi-Po caps are 151/416 inch from top to bottom.
This is a 289 High Performance...
This is a 289 High Performance block plucked from the engine bay of 5F07K100148-a one-off '6411/42 Mustang hardtop built for Henry Ford II.
The car is one of approximately...
The car is one of approximately 180 pre-production Mustang units built prior to the official March 9, 1964 startup date. The Hi-Po block really isn't unique. When you subtract the main caps, it's just another 289 block.
Some, but not all, early 289 High Performance blocks had screw-in oil gallery plugs. Despite urban legend, 289 High Performance blocks never had screw-in freeze plugs either. Those were reserved for the '69-'70 Boss 302 blocks only.
Factory-installed 289 High Performance engines had the vehicle serial number stamped into the righthand side of the block near the battery's negative-cable attachment point.
Here again is where fact blows fiction right out of the water. Ford never built a production 289 High Performance V-8 with a steel crankshaft. The Hi-Po has the same 1M cast-iron crankshaft as the 289-2V/4V engine. However, Hi-Po cranks were handpicked and Brinnel-tested for strength.
During assembly of this historic...
During assembly of this historic Hi-Po, we get to see the 289 High Performance main caps, which are wider than the 2V/4V caps. These guys are 151/416-inch from top to bottom. Mexican small-block castings also had the wider 151/416-inch main caps.
The 289 High Performance was fitted with the same basic C3AE connecting-rod forgings as the 2V/4V engines. Where they differ is the larger 31/48-inch bolts, compared to 51/416-inch bolts in the standard engines. This is a cool modification you can do on any 289 or 302 connecting rod to improve strength. The downside is, there is less steel around the 31/48-inch bolts, which weakens the rod to some degree. The best compromise is 51/416-inch ARP bolts, which are stronger and don't affect rod strength.
The 289 High Performance bottom...
The 289 High Performance bottom end isn't much different from what we find in 2V/4V engines. It has the same 1M cast-iron crankshaft and C3AE connecting-rod forgings. Pistons were cast from the factory, and most rebuilds use forged. If you're nervous about the cast crank, relax. Carroll Shelby went racing with this crankshaft and spanked Corvettes in the process.
Production 289 High Performance engines were fitted with cast pistons that were good for 6,000 rpm. Forty years ago, forged pistons weren't all that common, and they certainly weren't conventional in production engines due to cost and technology. At the time, forged pistons were available from the aftermarket.