Speed-O-Motive sells this 454-based 506ci big-block for $7,250. Power checks in at about 575 hp, making this one a good bang-for-the-buck deal. Wanna spend more? Factory 454 and 502 blocks support 800-plus horsepower. Aftermarket blocks like the Dart and Merlin can support double that or even more when power adders are used.