Diesel I6 5.9L Turbo

What it is

Bore is 102 mm, stroke is 120 mm and the compression ratio is 17.5:1, which comes to 5,883 cc across six cylinders. Those four figures match the Cummins 6BT 5.9, the 12-valve Dodge sold in the Ram. Nothing else here was copied from one. The curve on the dyno comes out of a diesel burn in two parts, a sharp premixed spike near top dead centre and a slower diffusion tail behind it, solved against crank-slider geometry while the plenum, the runners and the collector fill and empty around it.

The stroke is 18 mm longer than the bore and the rest of the engine agrees with it. The intake breathes best at 1,500 rpm and the rev limit is 3,000, which is where the factory tachometer marks red. Cummins rated the 1998 high-output version at 597 N·m at 1,600 rpm, and the shape is the whole point: everything arrives before you have finished pulling away. Put it beside the 4.6 petrol V8 on this roster, which is still climbing at 4,000, and the two curves barely belong on the same chart.

The compressor wheel is 75 mm and the turbine housing is tight, a truck turbo lit by 1,400 rpm. A tight housing costs backpressure, which sits above manifold pressure across the range and keeps the pumping loop a loss. The wastegate is regulating the whole way, from 7 percent open at 1,000 rpm to 77 at the limit, so the boost target is a spring setting rather than a turbo at its ceiling. It still reads low against the 14 to 16 psi a real 12-valve runs, because it stands in for a cap the model does not have. Diesel fuel mass here is air mass over one global smoke limit of 28, so every extra kilogram of air buys proportional fuel and no injector runs out. A real 6BT runs into its pump long before it runs short of air, which is how 5.9 litres and a bar of boost come to be rated 215 hp.

Things to try

• Widen Housing A/R from 0.13, or take Compressor Ø past 75 mm. Either one walks peak torque up toward the top of the rev range, which is nothing like how this engine pulls.
• Take Boost target from 1.25 toward the 2 bar absolute a real 12-valve runs. Torque keeps climbing, because once the air is there nothing in the model caps the fuel.
• Raise Redline past 3,000. The dyno keeps drawing curve, but a real 12-valve is on its governor across that span and the sweep here ignores governors.

Seen in

Mercedes-Benz E-Class (W210)

Same layout

1996–2002. Same layout, different engine: the E300 Turbodiesel's OM606 is a turbocharged inline-six diesel too, carrying a saloon rather than a ton of gravel.

Photo: miniperde · Pexels