FORCED INDUCTION

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The Benefits of Forced Induction The ­displacement and efficiency of a naturally aspirated ­engine limit how ­much power it can make. The engine can only inhale so much air because the atmospheric force that’s pushing air into the engine is only 14.7 lbs. per square inch at sea level. To make matters worse, atmospheric pressure decreases with elevation. Air density also decreases with temperature because hot air is thinner than cold air. Most stock naturally aspirated engines only achieve a peak volumetric efficiency ­of 75% to 85%. Small block or big block Chevy, Ford or Chrysler engines are ­usually ­limited to two valves per cylinder and fixed valve timing, but if you’re working on a late-model engine, multiple valves per cylinder and variable valve timing can help improve breathing ­efficiency. Other Tricks To Improve Airflow And Volumetric Efficiency In A Naturally Aspirated Engine Installing a higher lift, longer duration camshaft. Modifying the stock heads or replacing them with aftermarket performance heads that have larger valves and better ports. Installing an intake manifold with taller and longer runners to help ram more air into the cylinders. Installing a larger throttle body or carburetor (or multiple carburetors) that can flow more CFM (cubic feet per minute). Adding an air scoop or cold air intake ­system to help route cooler denser air into the engine. Improving exhaust scavenging with headers and crossover pipes that help improve air flow out of the cylinders. With such improvements, it is possible to boost an engine’s volumetric efficiency into the 90% range or even higher. But achieving 100% or higher volumetric efficiency (especially at higher rpms) usually requires some type of forced ­induction system such as a turbocharger or ­supercharger. Forced Induction A forced induction system overcomes the limitations of atmospheric pressure by pushing more air into the cylinders. Consequently, the engine’s power output becomes a function of how much