Last month we had a close look at the composition of pistons, and what this means in the real world for your performance engine. Obviously pistons are only a small piece of the puzzle when it comes to selecting parts to build a strong and reliable engine that will meet all your performance criteria. This month we will take an in-depth look at crankshafts and what you need to know to choose a suitable part.
Cast Versus Forged
Much like the pistons we discussed last month, there are two typical manufacturing methods for producing OEM crankshafts. For many years, the only offering available in road cars was a cast crankshaft. In this manufacturing technique, molten iron is poured into a crankshaft-shaped mould and allowed to cool. The process is cheap and the tooling used has a long service life, making it ideal for mass production. The cast item is also very close to the finished shape of the crankshaft, which reduces machining time. The downside is that the cast material has a low density and no real grain structure, which results in a weaker product. A cast crankshaft is also quite brittle, which is not a desirable trait for a performance engine.
Forged crankshafts, on the other hand, are formed by placing a hot piece of steel between two forging dies and forcing it into the shape of a crankshaft under immense pressure. This results in a denser material with a superior grain structure. That makes a forged crankshaft stiffer and stronger than its cast counterpart, while it is also less brittle, which improves its reliability. (more…)