The main constituent parts of a modern race engine are very similar to those we would have found in their ancestors of 40-50 years ago. Unless dictated otherwise by rules, we are likely to find aluminium structural castings, aluminium pistons, steel camshafts and a steel crankshaft. The Ford-Cosworth DFV Formula One engine conceived in the 1960s differs little in these respects from its descendant, the Cosworth CA2010 Formula One engine. However, although other engines might differ from these, we can say fairly safely that engines are made primarily of metallic components.
It is true that many modern engines will have some visible carbon fibre-reinforced polymer matrix composite parts, but often such materials are used only for airboxes/plenums and covers. There are a few race engine components that are routinely made from polymers. The most obvious example of polymer components are seals. From PTFE lip seals to elastomer O-rings, there is no viable alternative material. For O-rings and rubber seals, nitrile rubber is often OK, but where rubber seals are exposed to high temperatures or fuels, fluorocarbon rubbers are generally used.
Where stresses are low, polymer parts can be substituted for aluminium parts quite easily in order to achieve weight loss. Both filled and unfilled polymers are suitable for this purpose, and it is common to see these materials used for inlet system components where there is a constant supply of cool air. Cost savings might also be made where component quantities allow the use of polymer processing methods such as injection moulding or vacuum casting.
For small development batches, some 'rapid prototype' methods can produce cost-effective parts for engine use, although such methods are constrained in their use owing to the limited range of materials available. For moving components, there is very little use of polymers. Cages in high-specification ball bearings are commonly machined from polymer materials such as PEEK. Some oil pump suppliers offer polymer pump elements for scavenge pumps. Other minor components such as pressure-relief-valve pistons are good candidates for being made from polymers.
For anything more adventurous than this, we need look no further than the Polimotor engine from the 1980s, which is often mentioned here in RET-Monitor and in Race Engine Technology. RET issue 56 carried an article on the method of producing polymer cylinder blocks, and the SAE paper by Gaudette details some of the components used in this pioneering engine.
The simple 'rule' for this engine project was that components that ran at less than 500 F (260 C) would be considered for manufacture from a polymer or polymer matrix composite material. Most of the polymer components in this engine were filled polymers, and so qualify as composites. While 'composite castings' are being used in small numbers for race engine cylinder blocks again, the moving components in the Polimotor engine are of particular interest.
A number of parts were in some of the most demanding applications. The piston was partly made of polymer material, as was the piston pin. In the valvetrain the use of polymer parts was widespread, with cam followers, valve spring retainers and intake valve stems being tested and raced. The engine was an overhead cam unit, but trial parts were made for overhead valve (pushrod) engines too, with rockers and lifters being produced.
It is unlikely that we will see such heights of engineering reached again, as we have come to rely very heavily on the strength, stiffness and temperature resistance of metals for moving engine components. However, the work done almost 30 years ago perhaps points to the potential for polymer components to be used for a wider variety of applications.
Stowe, J., Race Engine Technology 'Insight' article, issue 56, August 2011
Gaudette, E.P., "Plastics within the Internal Combustion Engine", SAE Paper 850815, 1985
Written by Wayne Ward