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0.073 in. for the secondary. The initial timing setting remains at the factory setting of 10° BTDC, but the highest grade premium fuel is required to prevent detonation. This indicates relatively high combustion temperatures, and another consequence of this is that colder-than-stock sparkplugs are required. After much experimentation Spears has settled on Champion N59G gold-palladium plugs, gapped at 0.028 in., in conjunction with a Delta Mark X capacitive-discharge ignition system (plugs and CD ignition are not included in the turbo kit) as the best compromise. The problem, Spears explained, is that sparkplugs cold enough to survive temperatures with turbocharging have a tendency to foul in city-type driving. An easy way out would have been to enrich the mixture further, which would lower such combustion temperatures and let the plugs operate at less temperature differential between idle and maximum power. However, enriching the mixture reduces economy and probably would increase emissions; because Spears is trying to get this kit to pass for emissions he has decided to work with the lean mixtures. As it stands, with the colder plugs, after driving some distance in stop-and-go traffic there is a slight misfire for a few seconds the first time the boost pressure is kicked in. But our experience confirms what Spears has found: after this first burst of power the plugs clean off and fire properly.

How does it go? If you drive the car normally-accelerating gently and shifting at 3000-3500 rpm-you'll never know there's a turbo under the hood. Disappointed? Don't be. Because if you floor the loud pedal, the tone of the engine changes to

a mellow roar as the turbo cuts in at approximately 1900 rpm. Then events start happening quickly: the needles on the boost gauge and tachometer start a fast upward climb and the Mus- tang is propelled forward at a smooth but rapid rate. This Jekyll-Hyde personality is one of the biggest advantages a turbocharger has over radical camshafts, big ports and valves, high-flow carburetors and the other more usual means of increasing horsepower: it's there on demand when you want it but doesn't intrude when its presence isn't required. You don't have to put up with a lumpy idle, poor low-end response or any of the other driveability problems associated with the more common horsepower boosters. To save you the trouble of searching through your back issues of R&T for the pertinent figures here are the performance numbers for a 1974 Mustang II Mach I, a 1974 V-6 Capri and the Spearco turbo Mustang:

Very impressive. The Spearco Mustang not only walks all over a stock Mach 1 but runs away from a V-6 Capri as well. The turbocharger was not the only modification to the