Volkswagen W8

Volkswagen's 4.0 W8 — in the Passat B5.5, and nowhere else.

⚑ It is two VR6-style narrow-angle fours on a common crankshaft, at 72 degrees to each other — which is what makes a W rather than a V, and why an eight-cylinder engine fits transversely in a family saloon.

That packaging is the whole difficulty. Eight cylinders, four camshafts, two balance shafts and a great deal of plumbing occupy a bay designed for a four, and almost every job requires the front of the car removed. A quote made from any other engine will be wrong.

Its known items are the balance-shaft chain tensioners and the secondary air system, both of which fail with age and both of which are behind that packaging.

Roughly 11,000 were built, which puts parts and specialist knowledge somewhere between scarce and personal. The W12 in the Phaeton and Bentley uses the same idea at a different scale.