Preheat grill. Place corn ears in their husks over low-burning coals (or over low heat on a gas grill) and cover the grill. Cook corn, turning occasionally, until it is tender, 35 to 45 minutes. Transfer corn (still in husks) to a serving platter.

Meanwhile, heat 2 tablespoons butter in a small heavy skillet over medium heat until it is melted. Stir in chili powder and garlic and cook, stirring constantly, until garlic is golden and chili powder is fragrant, less than 1 minute. Transfer chili powder mixture to a food processor, then add honey, cilantro, remaining 6 tablespoons butter, salt and pepper, and pulse to combine. Transfer chili-cilantro butter to a bowl and serve with corn.