from chevyhiperformance.com
"To increase casting accuracy and minimize engine weight, the aluminum block and cylinder head of the Vortec 4200 I6 are made using a “lost foam” process. This casting technology provides both improved control of the manufacturing process and allows direct-mounted accessories that reduce vibration and weight. With the exception of the power-steering pump bracket, all engine accessories bolt directly to the engine."
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One of the most interesting aspects of the Vortec 4200 I6 is what’s called variable-valve exhaust timing. This feature adjusts the exhaust camshaft timing within a range of 25 degrees as engine operating conditions change. To do that, an onboard computer first collects several points of data including throttle position, engine load, and vehicle speed. From there, a control valve adds or removes oil from a cavity and piston chamber (see cutaway photo) at the front of the camshaft. Thus, advancing or retarding the exhaust camshaft not only enhances the torque curve, but also improves idle quality and reduces emissions. With the ability to change timing, a more aggressive camshaft profile can also be used."
