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Performance & Hotrod Business May '14

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56 n Performance & Hotrod Business n May 2014 PERFORMANCE inch range (or possibly greater). Always refer to the piston maker's recommenda- tion for forced induction applications. High boost requires "looser" ring end gaps. Also, if the engine will be aided by forced induction and/or the use of nitrous injection (in the 100-plus or greater horsepower boost range) consider the use of stronger top rings, such as steel rings nitrided or with a hardened coat- ing. Again, refer to the piston maker's recommendations, since specs will differ between naturally aspirated and boosted applications. Cylinder Bores The use of forced induction generates additional cylinder pressure when under boost. Cylinder wall thickness needs to be considered to prevent excess cylinder bore distortion (which will affect ring contact and sealing) as well as potential cylinder wall cracking. Wall thicknesses will vary among not only engine brands and models, but among blocks within the same family. Without delving into specific year/make/ model blocks, a general rule of thumb is that wall thickness should not be less than about 0.200 inches. During your build, the engine shop can easily check this with a handheld sonic tester that measures mate- rial thickness. My point is to always verify cylinder wall thickness, especially if the block has been or will be over-bored. Valves Exhaust valves in a boosted engine, par- ticularly with turbocharging, are exposed to greater heat levels. The most popular choices in terms of valve materials for forced induction applications is a high grade of stainless steel (commonly known as EV8) or Inconel, both of which will withstand higher valve temperatures. If you're not familiar with Inconel, the basic benefits, as opposed to stainless steel, include lighter weight, high strength and greater resistance to thermal dynamics. Inconel valves offer extremely high ther- mal resistance and are designed for high- heat applications as found in turbocharged, supercharged and nitrous applications. Camshaft In order to optimize the use of forced induction, ideally the engine will likely prefer a lobe separation angle (LSA) in the moderate-wide range, probably around 112 to 114 degrees. Generally, heavier valve springs are also required, depending on the amount of boost being created. The exhaust is opening against pres- sure, so this isn't a huge concern, but with regard to the intake side, you'll likely need higher-rate springs. Consult with the camshaft maker for its recommendation regarding spring pressures. Spark Plugs As a general rule of thumb, it's recom- mended to run one heat range colder than stock with a forced induction system. If you're adding a turbo or supercharger sys- tem, pay attention to the spark plug speci- fications provided in the kit instructions. Compression Ratio If you're building an engine specifically for forced induction, lowering the com- pression ratio allows more boost with the same octane. Static compression ratio (CR) refers to the compression ratio of your engine without forced induction. Final compres- sion ratio (FCR) refers to the compression that you'll have when full boost is applied. The formula for calculating final CR is as follows: (Boost divided by 14.7) + 1 X Static CR = Final Compression Ratio (FCR) At the top of the page is a compres- sion ratio reference chart that explains how static compression is affected by various forced induction boost levels. Note that the higher your final com- pression ratio, the higher octane fuel you'll need to prevent detonation. Final compression ratios above approximately 12:1 are not recommended for use with premium pump gasoline. Want more FCR? Then prepare to pay for race fuel. Upgrades to Consider for Durability • Pistons (switch to forged aluminum in place of hypereutectic) • Lower compression (where needed) to accommodate added amount of boost 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 6.5 7.4 8.3 9.2 10.0 10.9 11.8 12.7 13.6 14.5 7.0 8.0 8.9 9.9 10.8 11.8 12.7 13.6 14.5 15.3 7.5 8.5 9.5 10.6 11.6 12.6 13.6 14.6 15.7 16.7 8.0 9.1 10.2 11.3 12.4 13.4 14.5 15.6 16.7 17.8 8.5 9.7 10.8 12.0 13.1 14.3 15.4 16.6 17.8 18.9 9.0 10.2 11.4 12.7 13.9 15.1 16.3 17.6 18.8 20.0 9.5 10.8 12.1 13.4 14.7 16.0 17.3 18.5 19.8 21.1 10.0 11.4 12.7 14.1 15.4 16.8 18.2 19.5 20.9 22.2 10.5 11.9 13.4 14.8 16.2 17.6 19.1 20.5 21.9 23.4 11.0 12.5 14.0 15.5 17.0 18.5 20.0 21.5 22.9 24.5 BOOST (PSI) STATIC CR Compression ratio: If the engine is built with a static compression ratio of 9.0:1, final compression ratio will be 10.2:1 under 2 lbs boost, or 13.9:1 under 8 lbs boost, or 17.6:1 under 14 lbs boost. (Char t Cour tesy Silvolite/KB/United Engine & Machine) Thermal barrier coat- ings are worth seri- ous consideration for piston domes, valve faces, com- bustion chambers, turbo housings and headers or exhaust manifolds. (Courtesy Swain Tech Coatings) PHBMAY.indd 56 4/2/14 11:55 AM

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