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…)

Selecting new engine components for a rebuild can be a daunting task, with an endless number of brands and options to choose from. The parts you will need are dependent on a number of variables, which means there really is no one-size-fits-all answer for you. Over the years I have seen countless customers who have ended up with an engine combination that is either complete overkill for their application or, alternatively, is just not up to the required task. While in the first instance the overkill engine is only likely to leave a hole in your wallet, a combination that isn’t up to the task could just as easily leave a hole in your block.

This month we will take an in-depth look at pistons. We’ll discuss the pros and cons of cast versus forged pistons, and separate some of the facts from the fiction so you can make an informed decision about which pistons to select for your next build.

Cast Pistons

Cast pistons still remain the components of choice for production engine manufacturers. There are a number of advantages to the cast piston, however, it should be no surprise that their low cost is the reason they are favoured. Cast pistons also exhibit a very low rate of thermal expansion, which means they don’t expand much as the engine heats up. This allows the clearance between the piston and bore to be set very tight, which results in a very quiet engine. (more…)