M130

By 1967 the 2.5-liter M108 and M129 had reached the limit of their casting: the cylinders sat in pairs with continuous water jackets between them, and there was no metal left for a larger bore. The M130 evened out the cylinder spacing and cut those jackets back to a slot at the top of the block — enough water to cool it, enough material to take the bore from 82 to 86.5 mm. Stroke stayed at 78.8 mm, the crankcase stayed the same length, and displacement rose to 2,778 cc.

Two Zenith 35/40 INAT register carburetors gave 140 PS and the mechanical Bosch six-plunger injection 160 PS; a longer-duration camshaft with a recalibrated pump took the 280 SL and the 300 SEL 2.8 to 170 PS. American emissions law brought a lower-compression injected version with retarded ignition, cleaner at the tailpipe and thirstier everywhere else. The twin-cam M110 replaced it in cars from 1972 — but a 110-PS version at 7.8:1 compression kept working in the Unimog 404 until 1980, thirteen years after the engine was new.