Engine Tuning: Understanding the Origins of Today’s Car Tuning, Performance Tuning and ECU Remaps Part 3

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 Part 3 of 4 and looks at the topic of increasing Torque. Part 2 explained how to work out an Engine’s Horsepower and Torque.

There are two ways of increasing the amount of torque generated by an engine - either increase the capacity (or, more correctly, capacity times volumetric efficiency), or increase the length of the lever arm (or stroke).

For increased power, you can increase either (or both) the torque or the revs, at which that torque is generated. Increasing stroke will increase torque, so theoretically it would be good to have very long stroke engines. The problem is, if the stroke is too long, the volumetric efficiency decreases, particularly as the engine speed increases (which is why long stroke engines don't like high engine speeds, apart from the rotating friction and harmonics).

Now this decrease in engine speed more than compensates for the torque increase, which is why very high power output engines tend to have very short strokes (once again, engine strength issues ignored).

So as we can see the most important factor in increasing your engines performance is its volumetric efficiency.

The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions.