Diesel V8 6.7L HD

What it is

Bore is 107 mm, stroke is 92 mm and the compression ratio is 17:1, which comes to 6,618 cc across eight cylinders in a 90 degree vee. The Ford 6.7 Power Stroke and the GM Duramax 6.6 share that architecture and nothing else: none of these figures came off either engine, and there is no verified match to claim. The roster gets a heavy-duty diesel V8 with nothing bolted to its exhaust, which is a configuration the industry left behind decades ago. The pedal moves fuel, not air. No throttle plate sits in the intake to close, so the tract stays wide open wherever your foot is.

Air per cycle therefore answers to the head and the rpm alone, and that is the ceiling on everything else. Fuel at full rack is air mass divided by 28, which is where an unblown diesel starts smoking, so torque tracks the air this head can draw unassisted. Volumetric efficiency peaks at 0.95 at 2,000 rpm and the torque peak sits in the same place. Above it, breathing falls away while friction climbs on the square of mean piston speed, from 1.37 bar at the 800 rpm idle to 2.28 bar at the 4,500 limit. The useful band ends a long way below the limiter.

Each cylinder displaces 827 cc, and 17:1 leaves 51.7 cc of that above the piston at top dead centre. The model divides the burn's heat by exactly that volume to get peak pressure, which is how an engine with no compressor still makes pressure worth having: compression does the work boost does on the turbo version beside it. Starting it is a procedure. Glow plugs run 1.8 seconds, the starter turns 280 N·m at 220 rpm, and nothing fires below 360 rpm. The flywheel carries 0.85 kg·m² and each piston assembly 1.6 kg, so it idles at 800 rpm and takes its time reaching 4,500.

Things to try

• Open TURBO and press FIT TURBOCHARGER. Compression ignition is never refused, because that gate is a knock calculation and there is nothing here to detonate. What arrives is 2.4 bar absolute through a 97.6 mm compressor behind a 72 percent cooler, which is the roster's turbo 6.7 exactly, apart from the turbine housing: 0.17 derived here against the 0.12 that preset pins.
• Open ADVANCED and pull VE peak down from 0.95. Torque drops with it wherever the pedal is, since fuel is a fixed fraction of the air that got in and your foot cannot put back what the head stopped inhaling.
• Walk Inj timing out from 9 degrees before top dead centre toward the 25 the panel allows. Peak pressure climbs, then the burn starts pushing on a piston still travelling up and the compression stroke takes the gain back.

Seen in

Ford Super Duty

Same layout

2020 to 2022, the fourth-generation truck. Its 6.7 Power Stroke is this architecture with the one part the preset here leaves off.

Photo: Harrison Tincher · Pexels

GMC Sierra HD

Same layout

2024 onward for this face. The Duramax 6.6 has been GM's heavy-duty diesel V8 since 2001, in the Sierra HD and the Silverado HD alike.

Photo: Shane West · Pexels