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154 0412 Amc 04 Z

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Indy closed up the rear-chamber wall between the valves to yield superior quench. The KB piston (right, compared to the old Speed-Pro replacement forging, left) has a step that keeps the mixture out of the chamber's dead area, while the large flat dish area uses the whole chamber for a good burn. The result is a tumble-and-swirl-promoting 0.030-inch quench.