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Making Power From Big Block Fords

By Dave Emanuel

As noted last month, the first part of a big block Ford power program is to select the appropriate components and machine them properly. Part two entails coordinating the camshaft and valvetrain with an engine's intended use, and then bolting everything together using proven high performance techniques.

According to high performance Ford specialist Norm Wizner, Wizner Performance, Lilburn, GA, improper camshaft selection continues to be the most common cause of a performance shortfall. "We've had great success with our camshafts because we tie our recommendations to real world driving situations, said Wizner. "Too many people really believe that bigger is better. That's not always true with a race engine and it definitely isn't true with a street engine.

"I can't tell you how many customers we've had with engines that just didn't run the way they should have. In almost every case, the problem was a camshaft with way too much duration. When they installed one of our cams, the difference was night and day. In fact, one guy's car dropped its quarter mile time by more than a full second. It's not that our cam was so much better than the one he had, it was just matched to his engine combination better."

As an example, Wizner's camshaft selection for a 514 cid engine he built for a customer was one of his Street Boss Special hydraulic grinds with duration at .050", lift of 236 degrees for the intake lobes, and 240 degrees for the exhaust. Lift specifications are .566" intake and .580" exhaust. This is a relatively conservative camshaft considering the engine's displacement, but it's appropriate because the customer for this engine wanted to use his existing dual-plane intake manifold and 850-cfm Holley four-barrel carb.

With this type of intake system, the horsepower peak is in the 5,500 to 5,750 range so Wizner picked a cam that produces maximum power at this rpm level. A second consideration is that with 11:1 compression ratio, excessive duration takes cylinder pressures for a nose dive, which manifests itself as poor low-speed and mid-range torque.

In light of the fact that the 514 cid short block was topped off with a pair of Ford Motorsport Cobra Jet aluminum cylinder heads, the cam choice might seem a little too conservative. In fact, the relatively short duration of this particular Street Boss Special tends to compensate for the heads' huge ports. So what might seem like a mismatch, turns out to be a marriage made in heaven.

"The ports in the aluminum Cobra Jet heads are big, so they don't need much work," explained Wizner. "All I did on these was a bit of clean-up in the ports and some blending in the short-turn radius. We've spent a lot of time on the flow bench and developed a port shape that really works well."

Norm also said air flow is another consideration. "With these heads, you've got to concentrate on quality of air flow because if you fully port them, it will really hurt horsepower. So we concentrate on improving air flow without doing a lot of grinding. To go along with this, we also use a relatively short camshaft to pick up the velocity a bit and build cylinder pressure. What we wind up with is an engine that makes good torque -- 621 lbs./ft. at 3,800 rpm -- yet has enough port volume for decent top end horsepower," he said.

But the horsepower and torque figures in the accompanying chart (See page ?) only hint at the performance potential of this combination. With a longer duration camshaft, a 1050 Dominator and single-plane intake manifold, horsepower typically climbs to approximately 650 and torque rises to about 675; some low speed drivability is lost, but peak power is still within a reasonable rpm range.

One point to note is that with any high performance 460-based engine, it is essential that top quality head bolts are installed and carefully tightened to the recommended torque. This is critical because 460 engines have only two rows of head bolts. With so much space between bolts, any sloppiness in the tightening sequence can easily lead to head gasket failure. To guard against that, Norm uses premium quality head gaskets (in this case Fel Pro 1028) and torques the bolts in steps to 125 lbs./ft.

When the engine was all bolted together and run on the dyno, the wisdom of the Wizner approach was immediately obvious. In addition to the 620-lbs./ft. peak reading, the engine produced more than 550 lbs./ft. of torque over a 2,000-rpm band -- from 3,400 to 5,400 rpm. Horsepower wasn't too bad either; 570 at the peak (5,400) and more than one horsepower per cubic inch over a 1,400-rpm band, from 4,800 to 6,200 rpm.

Broad, flat power bands like these are what make a street engine fun to drive. Throttle response is immediate, the engine comes off-idle easily and the driver doesn't have to constantly work to keep rpm within a narrow range at the top of the scale. That's an important point to keep in mind. Most customers for high performance engines think they want horsepower, but they really want torque. Deliver an engine with a broad, flat torque band, and you're almost guaranteed to have a happy customer.

High performance assembly techniques

Parts costs aside, assembly of a high performance engine is a more expensive proposition than putting a plain vanilla engine together. The high operating speeds and increased stress levels to which the engine will be subjected leave less margin for error and demand that tighter tolerances be maintained.

That requires a good bit of hand fitting and massaging, which in turn takes time which we all know costs money. Piston ring fit is one example. In a standard rebuild, you simply purchase the rings according to bore size and install them. End gap falls where it may. In contrast, rings are typically individually fit to each cylinder in a high performance rebuild.

Ring fitting is a tedious operation that begins with the purchase of a .005" oversize set. Then a compression and second ring are installed squarely in a cylinder and the ends filed until the desired end gap is achieved. Although not as critical, oil ring rails should at least be checked to verify sufficient end gap. That process must be repeated for each cylinder.

According to Joe Moriarty of Total Seal, Inc., "All ring manufacturers face the same situation, it's difficult to supply rings that suit everybody's need for end gap. Requirements vary according to piston type, fuel being used and individual preferences. Bore diameter also influences the situation. If cylinders are bored to a specific diameter to achieve the required amount of piston-to-wall clearance, it can be impossible to achieve the desired end gap specification with standard ring sizes. File fitting rings is a lot of work, but it's the only way to be sure end gap is properly set."

Several studies have been done concerning the effect of end gap on ring leakage and they all agree that establishment of proper end gap pays significant dividends. Minimizing ring leakage increases horsepower and fuel efficiency while reducing oil contamination and oil temperature. So the end result is a better running engine that lasts longer.

Lubrication is another consideration, and one that is often overlooked. It's not at all unusual for an engine to sit for six months to a year after it's been rebuilt. In many instances the car in which the engine will ultimately be installed is also undergoing a rebuild process; initial firing won't take place until after the entire project is complete.

That being the case, the use of quality assembly lubes that will remain in place is essential. If all you do is oil up the cam lobes with motor oil, a cam lobe or lifter failure is almost guaranteed.

Clearances must also be carefully considered in a high performance engine assembly. Main and rod bearing clearances typically range between .002" and .0025", but the important point is that clearances are set precisely -- a tolerance of plus or minus .001" won't cut it. The same is true of piston-to-wall clearances. Most high performance forged pistons require clearances of .006" to .008", depending on bore size and material. If the manufacturer's specs are ignored or taken lightly, you'll wind up with pistons that rattle, or seize in the bore. Neither of these conditions is especially conducive to building customer satisfaction.

Most engine builders who specialize in high performance work trial fit components during machining and again prior to final assembly. So an engine is assembled at least twice before it goes out the door.

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