V4

A V4 engine mounts four cylinders in two banks positioned at an angle to each other, typically 60 to 90 degrees, forming a V when viewed from the end. The crankshaft runs down the center of the V, with each bank of two cylinders sharing a common crankpin or operating on separate pins depending on the design. This layout occupies less width than an inline four-cylinder engine while remaining more compact front-to-back than a V6.

V4 engines are relatively uncommon in automotive work because the V-angle creates an inherent secondary imbalance that requires careful tuning or a balance shaft to suppress vibration. The narrow bore spacing also limits displacement per engine length, making them less efficient than inline fours at the same power output. They have appeared in small-displacement motorcycles, marine outboards, and occasional light trucks, but never achieved widespread adoption in passenger cars.

Design and firing patterns

The crankshaft configuration determines firing order and vibration characteristics. Some V4s use a single crankpin with both connecting rods sharing it (like Lancia's historic design), while others mount the banks on separate pins offset 180 degrees. The shared-pin arrangement requires master and slave rods and produces a distinct sound signature. Firing interval depends on whether all four pistons fire at equal increments or in pairs.

V4s appear most often in high-performance motorcycles where the narrow width suits frame packaging, and in marine engines where inline configuration would make the shaft too long. Industrial generator and pump applications sometimes use V4 diesels rated from 15 to 40 horsepower. The layout allows manufacturers to use tooling and experience from V6 programs while trading some efficiency for compactness.