Engine Tuning: Understanding the Origins of Today’s Car Tuning, Performance Tuning and ECU Remaps (Part 4)

This collection of articles consists of four parts. They will help to explain the origins of Engine Tuning, explanations of the engine tuning process and how, the now popular car tuning and performance development industry works.

This article is final part of the collection and looks at Volumetric Efficiency and Piston Displacement. Part 3 introduced the topic of Increasing Torque.

When dealing with the topic of volumetric efficiency calculation, piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions.
An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder.

This is not possible, except by supercharging or turbocharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. Therefore, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.

Volumetric efficiency= Volume of air admitted to combustion chamber / Volume of air equal to piston displacement x100

Volume of air equal to piston displacement Put simply the volumetric efficiency is the measure of your engines ability to process the charge (air fuel mixture entering the engine).

For example an engine with a high volumetric efficiency would be the Honda F20 engine found in the Honda S2000 this engine produces 240bhp and 208nm of torque from a 2000cc displacement, this is achieved through finely calculated gas flows through the engine combined with high engine speeds.

But of course, any modifications or enhancements made to an engine must be accounted for by altering the values that control the air/fuel/ignition timing that the engine sees, in most modern cars this is all computer controlled by an ECU (engine control unit) and a specialist with the correct equipment can accurately alter and measure these factors to give your engine its optimum level of power and torque.