April '20

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APRIL 2020 THE SHOP 39 PRECISION ENGINE PICKING THE PUMP The pump I selected for the 422 small- block Chevy build example was a two-stage vacuum pump from Jones Racing, P/N VP- 9100-C. It is a gear-style pump with built-in heat sinks that allow the passage of oil, fuel or moisture without pump damage. Mounting involved bracket VP-9100-L- BM, 38-tooth radius tooth pulley FP-6106- 38-5/8, 38-tooth radius tooth pulley BG- 6108-38S, radius tooth belt 760-10 HD and a multi-part drive hub assembly that attached to the crank balancer. An adapter is secured to the crank snout, which registers this engine's MSD trigger wheel on center and provides a center reg- ister for the drive hub. The drive hub is then secured to the Fluidampr crank bal- ancer via three 3/8-24 bolts that also pass through the MSD trigger wheel. Note: Because the pump's 0.500-inch- thick bracket sandwiches between the block and the MSD 8600 trigger pickup bracket, it was necessary to mill 0.500-inches of material from the rear of the MSD bracket in order to maintain the pickup sensor alignment with the trigger wheel, since the pump bracket caused the pickup to move 0.500 inches forward of the trigger wheel. Note: When test-fitting the vacuum pump, check for possible interference between the pump's bracket and the block's fuel pump cover. If using an aluminum fuel pump cover, the bracket may interfere if the cover sticks out from the block surface, preventing the pump bracket from seating flush with the block. Mark the fuel pump cover, remove and grind clearance as needed. MIKE MAVRIGIAN owns and operates Birchwood Automotive in Creston, Ohio, where he builds custom engines and street rods, and performs vehicle restorations. He has written thousands of technical articles, as well as nine books on automotive technology during the past 30 years. Mike can be reached at (330) 435-6347 or birch- Visit Birchwood's website at A happy engine means a happy engine builder! While not mandatory for typical street ma- chines, the use of a vacuum pump can make a big difference in competition engines. This 632-ci big-block, 1,115-hp build features a Dart Big M block, Big Chief II heads and a whopping 15:1 compression ratio and is equipped with an external vacuum pump and race alternator. Note the slotted bolt holes at the vacuum pump mounting bracket. This allows easy adjust- ment of belt tension. Unlike a V-belt, a radius tooth belt does not require much tension, since the teeth provide the drive engagement. As a result, the elimination of high belt tension also helps to reduce parasitic power loss.

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