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Performance & Hotrod Business May '14

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54 n Performance & Hotrod Business n May 2014 PERFORMANCE Connecting Rods The added stress of any forced induc- tion system (turbocharger, supercharger, or even the occasional injection of nitrous oxide) places more strain on the rods. Switching from OE cast or powdered metal rods to quality forged steel rods is a must if you're planning to run about 450 hp or more. Which style is best? In theory, H-beam rods are stronger, but in reality an H-beam rod can be lighter while being as strong as an I-beam rod. Without going into too much detail, in many cases choosing between I-beam and H-beam boils down to either manufacturer availability and/or engine builder preference. Another beam style is the X-beam, which has been utilized in some die- sel applications (for weight savings) but is now being made available for various automotive gas-engine applications as well. The X-beam is sort of a mix of both I-beam and H-beam, with weight-saving grooves on both the beam faces and sides. This provides a substantial weight savings, while also increasing the beam surface area, offer- ing lighter weight while retaining strength. In summary, if you're planning to pro- duce in excess of about 450 hp, choosing a quality forged rod provides substantially more insurance as opposed to a cast or powdered metal rod. Just as important, or perhaps even more important, is the quality, or tensile strength, of the rod bolts. For any high- performance build, and certainly one that will feature forced induction, regardless of the type of rod being used, always use a high-strength aftermarket rod bolt such as those offered by ARP and others. Never skimp on rod bolts. Most hard-use (street high-performance and racing) applications will favor rod bear- ing clearance in the 0.002- to 0.003-inch range. Small-journal rods (2.00 inches or smaller) can get away with slightly tighter clearance, in the 0.0020- to 0.0025-inch range. Larger journals (2.200 inches and larger) may need slightly more clearance, in the 0.0029- to 0.0030-inch range. Forced induction engines (turbos and superchargers) tend to build more heat at Main studs (where appropriate for your engine design) provide increased main cap stability. Especially when deal- ing with an aluminum block, this also saves wear and tear on the threads, especially if the engine will be regularly disassembled and assembled. Always install head or main studs finger-tight. The clamping force will be achieved during nut tightening. Overtightening the stud itself can easily result in slight splaying, which will impose un- wanted force angles at the main caps. Obtain the highest-quality bearings available for your application. Anti-friction coatings are offered by bearing makers (or you can have your new bearings coated). An anti-friction coating provides a bit of added insurance against scuffing, for those instances where bearings may be momentarily starved for oil and for added protection during cold startups. These coatings are appropriate for high boost and/or nitrous applications where the crank and rods are exposed to abrupt forces (when hitting high boost or when nitrous is injected). (Right) The use of cylinder head studs offers an increase in clamp- ing force and stability, especially in applications where the en- gine may be exposed to routine teardowns. Clamping force is performed by tightening nuts instead of working and potentially wearing the threads in the block. (Left) Specialized thermal barrier coat- ings are available that are specifically designed to handle the increased heat generated for turbo use. Many coating shops often refer to this as a "goldcoat" coating. (Courtesy Polydyn) PHBMAY.indd 54 4/2/14 11:50 AM

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