1966 Shelby GT350 - How To Rebuild A 289 Hi-Po

In the Dec. '08 issue we knocked down a 289 High Performance V-8 pulled from Rolo Malschafsky's unmolested '66 Shelby GT350. The real news of our effort was the engine's originality. It had never been apart in 42 years.

Why tear down an original, low-mileage, and undisturbed 289 Hi-Po? Because even when mileage is low, engines need to be freshened up if you intend to drive the car. Seals get hard and leak. Piston rings lose tension and bores wear, causing blow-by and loss of power. Corrosion develops between moving parts. Bearings and journals wear. These things happen even when cars don't get driven. More than anything, an engine's oil needs heat in order to stay fresh and free of contaminants. When an engine sits, condensation develops on inside surfaces. With moisture comes acids and other contaminants that create even more problems. A long highway run gets engine temperatures to the point at which moisture evaporates from the oil. What's more, a steady diet of fresh gasoline keeps the fuel system healthy and free from gum deposits.

In last month's issue, JGM Performance Engineering tore down, inspected, and performed all machine work on Rolo's 289 High Performance engine. Now we're ready to put this engine together and see what it does on the dyno.

About Bearing Clearances
Main and rod bearing clearances make the difference between engine building success and failure. When you're running a high-performance engine, clearances need to be looser than with street stockers because journals run hotter. Because they run hotter, they run larger. Everything expands with heat-the crankshaft journal, bearing shell, and oil. You want good oil flow across bearings and journals to carry away heat. At the same time, you don't want sloppy clearances that can lower oil pressure.

Another important issue is crankshaft endplay. When endplay is excessive, it places the engine's moving parts at risk. Move the crankshaft too far fore or aft and you wind up with connecting rods in poor alignment with piston pins and rod journals. This can cause engine failure.

Main Journal Diameter: 2.2482-2.2490"Rod Journal Diameter: 0.1228-2.1236"Crankshaft Endplay: 0.004-0.008"

Why It Is Important To Degree
Blueprinting is something you should do with all engine builds, including stockers, because it ensures that there's no stone left unturned and no detail missed to bite you later. Although degreeing a camshaft and checking for true top-dead-center is believed to be "race only" by many, this is a step you don't want to miss. The first thing we do is check true top-dead-center and how it relates to the block and crankshaft. Not all crankshafts are true to mark, nor are all blocks.

Oil Pump Prep
Oil pumps need blueprinting, too. Rotor side clearances should be checked. The pressure relief valve must also be checked for smooth operation. The piston and spring should move freely without binding. When you are finished checking, fill the pump cavity with engine assembly lube, which will stay there until you fire the engine. Filling this cavity with lube provides a solid shot at lubrication to all major parts when the engine fires for the first time.

The Dyno Room
Whenever you build an engine like this, it's easy to get drawn into thinking that this engine will make more power than it did from the factory. However, factory horsepower and torque figures aren't always indicative of real-world power. Ford sales literature from 1966 tells us the 289 High Performance V-8 makes 271 hp at 6,000 rpm. Of course, that's an average of what you can expect from a factory original 289 High Performance engine-with some higher and some lower.

When Shelby weaved his magic, horsepower went to 306 at 6,000 rpm-again an average-with a modest increase in torque. Shelby got 306 hp with a dual-plane high-rise aluminum Cobra intake manifold and a 715-cfm Holley carburetor. Contrary to popular myth, Shelby American did not swap in a hotter cam. For one thing, it wouldn't have made economic sense. Shelby did easy bolt-on mods that also included a Cobra T-pan and Tri-Y headers, the latter of which also contributed to power.

Our Hi-Po engine operates at a disadvantage. From an automatic car, it doesn't have the advantage of a big carburetor. Instead of the 715-cfm Holley, it has a 480-cfm Autolite 4100. That's our 289's handicap-not enough carburetor for a 300-horse engine.

When Jeff Latimer set up our 289 High Performance Cobra V-8, he fine-tuned everything he could to achieve optimum power and efficiency. He fitted Rolo's Autolite dual-point with a PerTronix Ignitor II electronic ignition to eliminate ignition points. The result is smooth idle and good high-rpm performance. Jeff also took one more pass at the valves, adjusting them to 0.018-inch cold before fire up.

Because we were running a flat-tappet mechanical camshaft, we needed to break in the engine and also work-harden the cam lobes. Jeff fired the engine and held it at 2,500 rpm for 30 minutes to break in the camshaft.

So what did we learn from these corrected numbers? Our Comp Cams flat-tappet mechanical camshaft yields a broad torque curve where peak torque arrives at 4,500 rpm and passes the torch to horsepower at 5,200 rpm. In fact, peak torque is hard to define because it's there at 3,400 rpm and doesn't begin to waver until 5,000. This engine makes torque across a vast rpm window, and that's its greatest asset.

How could we have improved our numbers? First, with a 715-cfm Holley for higher horsepower and torque numbers. Secondly, a more aggressive roller mechanical camshaft with greater duration, more lift, and tighter lobe separation is available from Comp Cams. It wouldn't have hurt us to opt for the 351W firing order to improve crank load distribution and power. Aside from the Comp Cams stock grind Hi-Po camshaft and Pro Magnum roller rockers, our 289 High Performance engine is a stock rebuild sporting common sense improvements such as dynamic balancing, better gasket technology, hardened exhaust valve seats, Viton valve seals, and PerTronix ignition. The result is 291 hp and 300 lb-ft of torque.