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Edelbrock warns that its Performer RPM 409 heads must be limited to 0.550 maximum valve lift when installed on 348 blocks to prevent valve-to-block contact. Here a light checking spring and dial indicator are used to verify Edelbrock's warning with the head mounted to our 348 block. Sure enough, when pushed farther than 0.550, the exhaust valves come into solid block contact. We're running an Isky 0.639 solid-roller cam, so action is needed.