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How to Rebuild 4 Cylinder Engines for More Horsepower

by Sameca Pandova

When rebuilding an engine, you can opt to have additional work done to improve engine performance over stock levels. Your upgrade path will differ based on whether you want a naturally aspirated or turbocharged engine. In either case, more horsepower is developed by machining work on the head, replacement of valves and valve springs, raising or lowering engine compression, and replacement of bottom-end components such as rods and crank. The exacting nature of detailed head work is challenging and best left to a professional shop, but bottom-end and basic head-work can be accomplished by the dedicated home mechanic.

Port and polish the intake runners, and gasket match the exhaust ports. An engine head is nothing moire than a series of gas channels, directing air in and out of the engine. Modern engines feature cast components, and these often come with small blemishes and rough areas embedded in the metal. Using a die grinder with a carbide tip, you can clean up the intake ports, polishing them to a smooth shine. On the exhaust side, bolt up the exhaust manifold gasket and use the die grinder to make sure the exhaust ports fully match the gasket shape and size, as these ports are typically slightly smaller.

Replace the valves and valve springs with aftermarket units, or have a shop perform a valve job. The shape of the valves affects performance, and by removing material at the top of the valve's cap, you can improve airflow since you are reducing obstruction in the air channel. In addition to the valves, using titanium or high-strength valve springs will allow you to increase the redline on your engine, increasing your power band.

Installer a thicker or thinner head gasket. This is an easy way to make more power depending upon whether you are naturally aspirated, or turbocharged. For a naturally aspirated engine, a thinner head gasket -- or having a professional shop shave the head -- will increase compression, and thus increase power. On a turbocharged engine, a thicker head gasket will lower compression, which allows the engine to safely handle more boost.

Replace the crankshaft, rods and pistons with forged aftermarket units. Most engines come with cast internal components, by swapping to forge internals, the rods and pistons become far more heat resistant, which allows you to increase compression and timing in a naturally aspirated engine, or increase boost and timing in a turbocharged engine. In addition to more heat resistance, the forged pieces may be lighter than stock allowing for better throttle response. Some aftermarket companies produce stroker kits, which are complete bottom-end assemblies that allow you to increase the displacement of your engine via a revised crankshaft, rods and pistons. Stroker kits might allow you to turn a 1.8 liter engine into a 2.0 liter engine, which will generate more power.

Tips

  • While a home mechanic can clean up the casting on a head, a professional port and polish which is tested on a flow bench is the best way to optimize air flow on an engine head.
  • More power will mean more heat generation, which may tax your cooling system. Be sure to monitor coolant and oil temperatures carefully to determine if cooling upgrades will be needed.

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About the Author

Based near Chicago, Sameca Pandova has been writing since 1995 and now contributes to various websites. He is an attorney with experience in health care, family and criminal prosecution issues. Pandova holds a Master of Laws in health law from Loyola University Chicago, a Juris Doctor from Case Western Reserve University and a Bachelor of Arts in history and political science from Case Western.

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