Jim Clarke, chief engineer of Ford's advanced powertrain engineering department, claims that he has "a lot of equity" in both pushrod and overhead-camshaft engines, having been the engineering manager on Ford's 5.0-liter for seven years. But he vows that, ultimately, Ford's overhead-camshaft V-8 offers the potential for a smoother idle, better fuel economy, lower noise and vibration, and much more horsepower than pushrod V-8s.
"We could have supercharged this engine for even higher power levels and really gone for the gold," said Clarke, smiling. "But we really wanted to win without adding any tricks. If we supercharged, you'd probably be looking at maybe another 20 to 30 percent above the [380-horsepower] naturally aspirated engine. But in the end, we didn't want a one-off that took six Hail Marys to produce."
Clarke emphasizes that turbos or superchargers mean dealing with awesomely high underhood temperatures, intake charge intercoolers packaged into the tight engine bay, ugly hood bulges, and long-term durability problems. But should Ford decide to pull additional power out of the 4.6, Clarke stands behind the strengths of the engine's bottom end, which he claims will cope with up to 100 horsepower per liter.
For high-volume air intake, Ford specified a low-restriction air cleaner and a throttle body with twin 70-millimeter intake throats. Following the throttle body is a special hand-fabricated aluminum intake manifold, working in concert with variable-intake camshaft timing. The timing tweak is achieved with an electromechanical system that varies the cam timing by about 12 degrees, allowing low overlap for a silky-smooth idle or lots of overlap above 3500 revs for max power.
Clarke boasts that Ford's triumph has been lowering the five-valve engine's power peak to between 6000 and 6500 rpm, while other carmakers must spool their five-valve engines up to about 7500 rpm to obtain maximum output.
Of course, if an engine swallows additional cubic feet of air, additional fuel must also be mixed. For this, Ford's concept-development people chose dual-spray injectors with a much higher flow rate than stock. Then, to put the squeeze on this more potent intake charge, the engineers pumped the compression ratio up to 10.50:1 from 9.85:1. The spent gas is discharged through two exhaust valves and dumped into fabricated steel headers coated with ceramic, rather than with a heavy, restrictive cast-iron manifold.
In keeping with the sophisticated character of this sporty 4x4, shifts are handled by a four-speed Ford 4R70W automatic transmission equipped with the beefier torque converter of the Lincoln Mark VIII. The power flows smoothly from the transmission to all four wheels through a pavement-grabbing viscous-type all-wheel-drive system.
Independent Thinking
Turning a standard, live-axle Explorer into an independently sprung Tremor was no backyard project.
To reengineer the full-frame Explorer's unibody to accept the Thunderbird's smooth and quiet corner-bending rear suspension, Ford turned to one of its large suppliers, Multimatic, Inc., of Markham, Ontario, and a small division of that company, called MTC. Multimatic currently supplies Ford Motor Company with everything from complicated instrument panels to simple door hinges.
Before the T-bird axle could be grafted into place, major surgery was performed on the Explorer's frame. First, the two riveted main frame rails were removed. A custom-built frame extension was then installed in their place to properly pick up the Thunderbird's suspension subframe mounts.
The second major modification to the frame rails was boxing (closing the open side of) the C-channel sections that run under the passenger-compartment floor. While plenty sturdy enough for wrenching off-road requirements, it was feared the C-channel steel might get twisted out of shape under the supersavage torque loads pumped out by the more-potent V-8.
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