The V8 engine is a favourite among us enthusiasts due to the easy power and torque output they generate. But mainly, we just love the noise of the things. However, not all V8 engines are created equal, and two primary types of V8 engines stand out: the flat-plane crank V8 and the cross-plane crank V8.
The main difference between a flat-plane crank V8 and a cross-plane crank V8 is how the crankshaft is designed. The crankshaft is the engine component that converts the up-and-down motion of the pistons into rotational force, which then drives the wheels. Basically, it is the bit at the bottom of the engine that all pistons connect to within an inline or V-shaped engine. The crankshaft in a flat-plane crank V8 is designed so that the four throws are 180 degrees apart from each other, with the crank pins positioned on the same plane. This results in a more evenly spaced firing order, with cylinders firing in alternating banks, and gives the engine a smoother, higher-pitched sound. The typical firing order is L-R-L-R-L-R-L etc.
On the other hand, a cross-plane crank V8 has its crankshaft designed in such a way that the four throws are 90 degrees apart, with each bank of four cylinders firing in sequence. This results in an uneven firing order, which gives the engine a distinct rumble that is often associated with V8s.
The difference in the firing order also affects the power and torque output of the engine. In a flat-plane crank, the more evenly spaced firing order means that each cylinder has more time to recover between power strokes. This results in a higher peak power output but a narrower torque band. In contrast, a cross-plane crank V8 produces more torque at lower RPMs due to the overlapping firing order, making it a better choice for vehicles that need low-end power, such as trucks and SUVs. The firing order on these are L-R-L-L-R-L-R-R etc.
Another factor that contributes to the difference between these two engines is their respective weights. Due to the design of the crankshaft, a flat-plane crank V8 is generally lighter than a cross-plane. This is because the flat-plane crank doesn’t require counterweights to balance the engine, which are needed in a cross-plane crankshaft to offset the uneven firing order. In terms of usage, flat-planes are often used in performance cars and race cars, where high horsepower and high redlines are required. On the other hand, cross-plane crank V8 engines are often used in trucks, SUVs, and muscle cars, where low-end grunt is much more important.
To summarise, the main difference between flat-plane crank V8 and cross-plane crank V8 engines lies in the design of their crankshafts, resulting in differences in sound, power and torque output, weight and usage. Choosing between the two ultimately depends on the intended usage of the vehicle and the desired performance characteristics.
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