Beginner's Guide to Engine Performance Parts and Components - LovingLocal
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cloose-up of subaru impreza performance engine

Beginner’s Guide to Engine Performance Parts and Components

If you’re serious about performance and a faster and more responsive car, you need to dig deep into the engine block. Higher horsepower numbers, better torque and low-down pulling power often involves swapping out the stock “bottom-end” parts – the pistons, connecting rods and crankshaft. This is where a few careful modifications can produce some interesting results when taking your car out for a spin on the track.  

Let’s take a closer look at how each of these engine parts functions, and how this can be improved.  


close-up of pistons

Pistons are the parts that are first in line to take the hit from the combustion of air and fuel. They sit in the cylinder bore and push down on aptly named connecting rods to transfer that power down to the crankshaft, and from there to the wheels. They consist of the piston crown and piston skirt. Along the skirt are the piston rings. The role of the crown is to push the piston downward when hit by the pressure from expanding gases in the combustion stroke. The skirt guides the assembly in the cylinder, and the rings help in lubricating the whole assembly and prevent the engine from seizing.  

All pistons today are made of aluminium. Pistons in stock engines consist of 4032 aluminium and a higher silicone content that helps prolong engine longevity, and reduce noise from vibrations. For performance applications though, 2618 aluminium has less silicone but can endure more expansion at faster engine speeds. If you’re often hitting redlines, then these are the ones to get. Another distinction is how they’re made. Forged pistons are much tougher than lower-cost cast pistons, since they endure careful machining that makes them handle the bigger bangs in the power stroke much better.  

A common upgrade, when low-down torque is considered, is a stroker engine. This features pistons with a longer stroke. Stroker kits are designed to increase engine displacement, by thrusting the piston further down the cylinder bore, in effect creating more space for a bigger bang. Here there are also changes to the connecting rod and crankshaft designs.  

Connecting rods 

close-up of connecting rods

The connecting rod is what connects the pistons to the crankshaft. Often called conrods, they too are a sum of their parts. The bottom end of the part that sits along the crankpin journal (or more precisely, on bearings) is called the conrod cap. It consists of two separate parts connected with a bolt on each side. The larger portion of connecting rods comprises the conrod shaft or beam. This needs to balance lightweight and overall strength in getting the linear movement of the pistons down to the crankshaft. At the “top end” of the conrod is a circular opening with an inserted bush bearing that slots the piston pin, effectively fitting the connecting rod to the piston.  

There are two types of connecting rods. They get their names from the cross-section cuts that resemble letters. H-beams resemble the capital H, and I-beams resemble the capital I. The different designs also mean different applications. Generally, H-beams can better handle more expansion and contraction as the piston moves up and down the cylinder bore. This mechanical stress is increased as the engine spins faster, and reaches higher RPMs. H-beams are better machined, stronger and as a result, more expensive. They do however come in as heavier, but are better suited for performance cars. Adversely, I-beams are conrods you’d find in lower-powered production cars. Their advantage is that they are cheap to make and buy, and come in lighter. Some higher-end I-beams are preferred for higher revving engines, particularly in turbocharged four-pots. 

Like pistons, connecting rods differ in the materials and how they’re made. Smaller displacement engines, both in petrol and diesel guise, are made of cast steel conrods. Higher compression diesels and performance petrols use carbon steel. A better material though is aluminium. Aluminium connecting rod is found in turbocharged and supercharged engines, which can reach higher revs. Aluminium is more suitable to the higher forces that stretch and bend the conrod thousands of times a minute in faster spinning engines. More recent is titanium. This can be found in one-off engine builds found in high-performance track cars.  

Cast conrods feature in most production engines, whereas forged and billet connecting rods are more in line with performance applications. Of the three, billet conrods are the most expensive, and by a considerable margin.  


Close-up of perfromance cranks

The crankshaft is the largest engine part here. It converts the linear movement of the piston and conrod combo into rotational force. This turns the flywheel and gears in the transmission, which then turn the wheels. Crankshafts are more complex in design and have multiple parts. This includes the main journals, around which the whole assembly spins, the crankpins or conrod journals, that connect the conrods, crankshaft arms, that connect the main and conrod journals, and counterweights to balance the whole thing as it spins in the crankcase. The crankshaft connects to the transmission via the flywheel.  

Performance crankshafts differ from stock production variants much like performance pistons and conrods do. They are made of high-strength forged or billet alloys. Different treatment processes help in increasing overall rigidity to ensure that the crankshaft can spin at higher revolutions, while undergoing the tremendous stresses of twisting and rebounding during each engine stroke. Higher performance cranks are also those that shed some weight over the stock variants. Lighter is always better, that is when overall performance is backed up by the required material strength. To make sure that the engine performs at its best, performance crankshafts also feature better lubrication.  

Kits with carefully matched pistons, conrod and crankshafts are sold to boost performance in a range of stock engines. 

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