Jim Smart
May 1, 2005
Photos By: Chris Richardson

Although most of the Hi-Po bottom end is shared with the 2V/4V engines, two items aren't: the harmonic balancer and slide-on counterweight. They're there for an important purpose: balance. The 289 Hi-Po has 3/8-inch connecting-rod bolts, which adds weight to the reciprocating mass (piston and rod assembly). This called for a wider harmonic balancer and the added counterweighting from the slide-on counterweight.

Camshaft

The 289 High Performance V-8's personality comes from an aggressive mechanical flat-tappet camshaft that does its best work at high revs. Peak horsepower and torque come in around 6,000 rpm. For a flat-tappet camshaft you can use on the street, the C3OZ-6250-C factory bumpstick is aggressive, with .460/.460-inch valve lift and 310/310-degrees of duration. Lift at the lobe is .298/.298 inch. Raw torque and horsepower come on strong in the high revs.

Fuel Pump

All small-block Fords of the period were fitted with Carter fuel pumps. From 1964 to 1965, it was a screw-together Carter pump with the fuel filter. From 1966 to 1967, Ford used a sealed Carter pump without the filter canister. The Hi-Po engine differs in volume: It delivers more fuel than its 2V/4V counterparts.

Clutch & Flywheel

As you might expect, the Hi-Po employed more heavy-duty driveline components. Manual transmission applications had two basic types of Borg & Beck, three-finger clutches that measured 10.4 inches in diameter. Much of it had to do with spring pressure. Because early Hi-Pos struggled with clutch slippage under hard acceleration, Ford went to a stiffer clutch for 1967.

Classic Mustangs have always suffered with clutch-release bearing and linkage woes because the old-fashioned three-finger clutch yields great pressure on the release bearing and linkage. No matter what you do with the bellcrank clutch linkage, it will not stand up well to Borg & Beck clutch stress. You can count on failure at some point in clutch service life.

Today, the Hi-Po solution is the installation of a Centerforce Dual-Friction clutch and flywheel package to improve driveability and performance. The Centerforce clutch offers light clutch-pedal effort because it's a diaphragm-style. It gets even better with the flyweights on the diaphragm fingers. As engine revs increase, the flyweights place more pressure on the fingers and disc, eliminating slippage. This is a terrific design that offers the best of all worlds.

Cylinder Heads

Our greatest fascination with the 289 Hi-Po is likely its unique cylinder heads. Urban legend has always given the Hi-Po head larger ports and valves than other small-block Fords, which has never been true. Valvespring pockets for stability and screw-in rocker-arm studs for dependability make the Hi-Po head unique, because the more common press-in studs tend to pull out with aggressive camshafts and high revs. Outside of these factory modifications, the Hi-Po heads are virtually the same as the 2V/4V heads. Spotting a 19, 20, or 21 cavity number in the corners of the castings outside of the valve-cover areas on the exhaust side quickly identifies Hi-Po heads.

Enter text here.These heads were fitted with stiffer valvesprings for obvious reasons: to reliably slap the valves closed at high revs. Spring pressure was approximately 350 pounds on the Hi-Po heads. Smaller damper springs were also used.

Look for casting numbers C3OE, C4OE-B, C5OE-A, C5AE-E, C7ZE (service head), and C8ZE-B (also a service head). The C8ZE-B service head does not have the two-digit cavity number mentioned earlier.