Opel C26NE / C36GET / C40SE

Opel's big straight-six — the 2.6 C26NE, 3.0 C30SE and the enlarged 3.6 and 4.0 — in the Omega and Senator.

⚑ The C36GET is the Lotus Omega's engine and is the reason to know this family. Lotus took the 3.0 C30SE, bored it to 3.6, added two turbochargers and produced what was briefly the fastest saloon in the world. Almost nothing written about it applies to the naturally aspirated sixes, and the reverse is equally true.

The C40SE is the same idea without turbochargers — 4.0 litres, built by Irmscher — and both are rare enough that parts are a specialist matter rather than a scarce one.

On the ordinary sixes the recurring items are age: a distributor that fails with heat, an air-flow meter that skews fuelling as it ages, and belt-driven camshafts on an interference design.

These are cam-in-head engines, an Opel design where the camshaft sits in the head but operates the valves through rockers — valve adjustment is a real service item, unlike on the hydraulic-tappet engines around them.