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NHRA recently modified its rulebook to allow legal-replacement blocks, due to the scarcity of original, virgin castings. This 413ci Pure Pontiac engine is comprised of a MR1 cast-iron block, a ’70 Ram Air IV intake, and code-614 R/A-IV heads with absolutely, and we mean absolutely, no porting. What’s the contraption inline with the inlet radiator coolant hose? It’s another of Burton’s tricks—a one-way flapper valve, which allows him to quickly circulate ice water through the block to improve his engine’s performance in heads-up competition.