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Performance & Hotrod Business May '14

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May 2014 n Performance & Hotrod Business n 53 an angle that aims outward toward the main web side areas. Not all OE blocks will accommodate a modification to four-bolt or four-bolt splayed arrangements. If you currently have a two-bolt-main cap block, you may need to purchase a block that was originally made to accept four-bolt caps. Main bearing clearance will depend partly on block material. Aluminum blocks tend to expand more than iron blocks, allowing a slightly tighter static main bearing clearance on an aluminum block. The rule of thumb is to run 0.001 inches per inch of crankshaft journal diam- eter. For a boosted engine, some builders prefer to add about 0.0005 inches in order to generate a greater oil wedge to support the crank during operation. Again, in general terms for most V-8 engines, main bearing clearance will run in the 0.0025-inch range, but naturally this will vary depending on the specific engine. If bearing clearance is too loose, the engine's oiling system may not be able to keep up with demand. Crankshafts The greater the horsepower, the greater the stresses experienced by the crankshaft. For any high-performance build that's expected to spit out in excess of say, 450 hp, moving to a quality forged crankshaft is an intelligent move. Forged steel cranks are stronger than cast cranks and will better withstand the stresses imposed by greater cylinder pres- sures. Depending on the power (and boost) level and depending on how the engine will be used/abused, a cast crank may or may not survive. If you're build- ing the engine from scratch and plan to use a healthy amount of boost, don't even consider a cast crank. Note: If you plan to run a belt-driven supercharger, the crank snout will experi- ence greater stress, which is yet another reason to use a forged crank. Also, bear in mind that an OE design may feature a keyed crank snout or (in the case of the GM LS engine, for example) the snout may feature no key, using a press-fit damper. If you plan to run a belt-driven supercharger, make sure that the crank snout will accom- modate this. Forced Induction Depending on the design of the block, four-bolt main caps may feature vertical bolt design at all four cap bolt locations, or may feature the outboard bolt loca- tions at an angle (called "splayed" cap design). The angled bolts provide added rigidity to better withstand increased stress. If you're building an engine that will experience high boost and increased stress, a quality forged steel crank is the only way to go. Performance aftermarket rod bolts feature machined dimples at each end of the bolt. This accommodates the use of a rod bolt stretch gauge when the builder prefers to tighten by monitoring stretch instead of only a torque value. Tightening by monitoring bolt stretch is more ac- curate, eliminating friction variables. Stretch tightening allows you to ac- curately measure the bolt's stretch to achieve proper clamping force. Rod bolt makers and rod makers will provide both torque and stretch specifications. Always use only high-quality after- market performance rod bolts. Al- ways adhere to the rod bolt maker's recommendations for lubrication, as this can affect tightening torque lev- els. Be aware that a different torque specification will be needed when using oil versus a moly lube. When applying lube to the rod bolts, coat the underside of the bolt head in ad- dition to the threads. (Left) Steel billet main caps, while not necessary for every build, will certainly provide added insurance in a high-boost build. Performance aftermarket steel caps are normally made with a slight undersize, requir- ing align-honing to achieve the de- sired main bore alignment and bear- ing housing diameter. PHBMAY.indd 53 4/2/14 11:49 AM

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