In engines with overhead camshafts, the choice of cylindrical translating followers is very common, both in passenger car and bespoke race engines. These are in the form of ‘inverted buckets’ (also called tappet buckets), with the flat ‘bottom’ of the bucket being the contact surface between cam and follower. Other types of cam followers, such as finger followers, may offer a number of advantages – including lower reciprocating mass,...
An important element in improving engine performance is the optimisation of the valve lift curve to maximise the mass of trapped charge in the engine. In an engine with an overhead valve (pushrod) valvetrain, the change from flat-faced lifters (also known as flat tappets) to roller lifters has given design and development engineers greater freedom when synthesising new lift profiles. It is true that the fastest NASCAR class, Sprint Cup, has engines that are equipped with flat tappets, but...
If we look at the types of engines used in various car racing series worldwide, there is a very definite split between the US and elsewhere. The US has a hugely successful racing structure that predominantly uses pushrod (overhead valve/OHV) engines. From those racing at the local tracks right through to NASCAR Sprint Cup at the very top of the closed-wheel racing tree, the engines are based on a very similar architecture, namely that of production pushrod engines. Even the bespoke Sprint...
Valve springs are often the most highly stressed parts in any race engine. While some types of race engine don’t have valve springs – two-stroke, Wankel, four-stroke desmodromic or four-stroke with pneumatic valve return – most of the race engines we encounter will be equipped with some form of wire spring. For modern engines valve springs will generally be the familiar helical spring. In their unending quest to make the engine perform better through improved breathing,...
The function of the valvetrain in any engine is critical to its operation. In a race engine it is often an area of constant development; with engineers striving continually to improve the engine’s breathing characteristics or working towards higher engine speeds. Improving the trapped mass or inlet charge increases torque, and increasing engine speed increases power. The development of the valvetrain often includes new camshafts, valves, valve springs and spring retainers. The...