Crossplane

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The crossplane or cross-plane is a crankshaft design for V8 engines with a 90° angle between the cylinder banks.

The crossplane crankshaft has four crankpins, each offset at 90° from the adjacent crankpins. The crankpins are therefore in two planes crossed at 90°, hence the name crossplane. A crossplane crank may have up to five main bearings, and normally does, as well as large balancing weights. Crossplane V8 engines have uneven firing patterns within each cylinder bank, producing a distinctive burble in the exhaust note, but an even firing pattern overall.

The other design for a V8 crankshaft is the flatplane crankshaft, with all crankpins in the same plane and the only offset 180°. Early V8 engines, modern racing engines and some others used or use the flatplane crankshaft, which is similar to that used in a straight four or flat-four engine. Flatplane V8 engines may use any angle between the cylinder banks, with 60° and 90° the most common, however Ferrari uses 65°. They lack the V8 burble and the inherent mechanical balance of the crossplane design, but do not require the large crankshaft balancing weights. Modern flatplane designs often incorporate a balance shaft, which is not needed by the crossplane design.

Crossplane V8s tend to be of large capacity, such as 5 liters and above, because the complex crankshaft and its many balance weights make the engine relatively slow-responding (like a heavy flywheel). A large engine does not have to be "revved" as hard to produce the desired power. European flatplane V8s can be as small as 2.5 liters, because the lighter crankshaft - the big ends balance each other with minimal need for additional balance weights - allows them to be more free-revving.

The crossplane design was first proposed in 1915, and developed by Cadillac and Peerless, both of whom produced flatplane V8s before introducing the crossplane design. Cadillac introduced the first crossplane in 1923, with Peerless following in 1924.