COMPRESSION RATIO Increasing the compression ratio (CR) is often one of the first engine performance modifications. Squeezing the air-fuel mixture into a smaller space increases its temperature and ease of ignition; thus the rate at which heat is extracted from the fuel. Engineers call it “thermal efficiency.” MODIFICATION TECHNIQUES Common techniques to increase CR include: (1) Installation of a thinner head gasket. (2) Installation of “domed” or “pop-up” pistons. Check for adequate “piston-to-valve” clearance at TDC. Camshafts with more overlap
require more clearance. A good rule of thumb is 0.080″ for intakes and 0.100″ for exhausts. FORD RACING CAMSHAFT USAGE The durations shown in this chart are S.A.E. durations. The descriptions within each group of cams show performance characteristics and basic modification recommendations required to achieve desired performance. DURATION PERFORMANCE ENGINE/VEHICLE USAGE (SAE) CHARACTERISTICS AND MODIFICATIONS 270-290 Good idle quality Use with stock or slightly modified engine, and low RPM torque. stock axle gears and with A.T. or M.T. 290-300 Fair idle quality. Good low-to- Will work with stock or modified engine. mid-range torque and horsepower. Can use stock axle gears and with A.T. or M.T.
Tags : air fuel mixture, racing camshaft, axle gears, performance duration, head gasket, thermal efficiency, ford engine, valve clearance, ford racing, rule of thumb, performance engine, camshafts, performance modifications, performance characteristics, engine performance
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