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11 4160 series Holleys such as the 390s and 465s, use a secondary metering plate rather than a secondary metering block with removable jets. If you know what you're doing, the metering plate's fixed jet orifices can be opened up, or alternatively, metering plates are available in several sizes. Blood Enterprises' James Leahy found it necessary to richen the secondary side of the 465s only, and drilled the plate's standard 0.054-inch jets to 0.059. This procedure was done in small increments and retested on the dyno for AFR. The point is if you go too big, you'll need to start over with another metering plate.