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Bolt-on Performance: Mustang II
Teaching a New Horse Old Tricks
by Jon Asher
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Like most late-Seventies automobiles, the Mustang II King Cobra travels about at an unhurried pace. It has the graphics, the handling and the aura of an exciting car. The one element that is undeniably lacking, however, is horsepower. Scarcely had Pro Stock World Champion Dyno Don Nicholson completed his last pass in the new King Cobra during last month's test session ("Snake Charmer," June CC), than thoughts about remedying that situation began to emerge. The small-block Ford has always been a creditable performer, although one is hard pressed to see the legacy of the 271 hp 289's that powered the original Mustangs in the equipment-encrusted 302 that inhabits the Mustang II's engine bay. It became a challenge to revive Ford's short-stroke, large-bore small-block - for while the heads, manifold and camshaft have all become more restrictive to meet emission and mileage goals, under all the hoses there still lies a V-8 with soul.
Reviving the slumbering horsepower called for practicing the hot rodder's basic art - bolt-on modifications. For, despite the internal engine changes which have been adopted, any internal combustion engine still responds to better breathing. In terms of hardware, this means a carb, manifold and header installation. With a little patience, some careful work and a weekend's time, even an engine as seemingly complex as Ford's detoxified small-block will respond to a new induction and exhaust system.
Like most new cars, the 1978 Mustang does present some built-in limitations which can't be circumvented without considerable effort and expense. Ford's small seven-inch rearend assembly in particular is less than ideal for performance purposes, especially considering that a 3.00:1 gearset is the lowest ratio available. To compound the problem, limited-slip differentials are also unavailable. The only way to get a more mechanically advantageous set of gears underneath the '78 King Cobra is to install a larger eight or nine-inch Ford rearend assembly with a numerically higher gear ratio. This kind of work requires custom fabrication work, but for the very serious performance enthusiast, the investment in both dollars and time may be worth the results.
Since Nicholson's efforts had revealed that the stock 195/70R13 tires were inadequate at the dragstrip starting line, we went looking for something with a wider footprint. A set of 8½-inch-wide E60x14 Firestone Super Sports got the nod. Since the change in tire size required new rims, the stock wheels were replaced with Western Wheel's new Cyclone II aluminum spoked wheels. The wider rubber and natural aluminum rims augmented the King Cobra's already awesome image.
Manifold and carburetor changes on any late-model car can be confusing for the unwary. At first glance, there appear to be more hoses and fittings underneath the hood than on the inside of a Saturn rocket. But the aftermarket manufacturers have designed their street manifolds to retain all emission control equipment, so an intake system change becomes a matter of swapping parts. Holley has a Street Dominator single-plane aluminum manifold that's both lightweight and efficient, but some minor work may be necessary before it can be used effectively. First, since Ford's '78 EGR valve assembly, which is about ½-inch wider than their earlier models, bolts directly to the manifold (instead of fitting beneath the carburetor as it does in stock trim) you'll need a replacement unit from a retail parts supplier or Ford dealership (PN D6AZ-9D475-B). Bob Jennings Automotive in Sepulveda, California supervised the Mustang's transformation. He advises that the large vacuum fitting behind the carburetor boss on the Holley manifold will need to be shortened if you're planning on retaining the OEM air cleaner and its accompanying fitting.
Jennings recommends Holley's 6619 carburetor for this installation. With 600 cfm, it's got considerably greater capacity than the stock Ford two-barrel induction system, and it can be easily adapted to the stock emission system on almost all Ford cars. Installing this particular carb requires slightly reworking the throttle linkage. To get full throttle, you'll have to either custom fabricate a linkage "tower" to hold the end of the throttle cable, or you'll have to cut the stock tower down about one inch.
With Nicholson at the controls, the King Cobra recorded a best of 17.06/80.69 in stock trim. After installing the four-barrel, a set of headers and retarding the timing three degrees to eliminate a discernable ping under hard acceleration, the car was scheduled for a return engagement at the track to see just how much the bolt-on power plan had helped its performance.
Despite the Firestone Super Sports' 8½-inch-wide tread pattern, it was necessary to almost bog the car off Orange County's starting line to prevent excessive tire spin. With the exhaust from both headers routed through a single catalytic converter and tailpipe, the elapsed times improved a full three-tenths to 16.76, while the top speed went up almost two mph. When the headers were uncorked, the little 302 came to life. Shifting at 5000 rpm on the Mustang's electric tachometer (some 1500 rpm higher than with the headers closed), the car notched a 15.96/88.93, a full 1.1-second improvement over the stock quarter-mile elapsed time, and almost nine mph faster. On the street, it's clear that the addition of a second exhaust pipe and catalytic converter would be beneficial. Despite the headers' design efficiency, there's considerable backpressure with all the exhaust funneled through a single pipe.
Quarter-mile clockings are only a partial measure of a car's performance. Knocking more than a second off an automobile's elapsed time is an improvement a driver can feel. Much more difficult to quantify is the difference in how the car behaves in traffic or on the open road. In these situations, the modified car is just flat-out fun. Performance cars are still being made; you just have to be willing to finish the job they started on the assembly line.
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