The other new engine is the Cummins diesel, still a 24-valve 5.9L inline-six, but now with common-rail injection. The new fuel injection allows for variable (and multiple) injection events per cycle, so emissions, economy, and power are all improved.
But the most noticeable improvement is noise level, with most of the diesel knock absent at any speed or load: If you park an '03 Cummins next to a previous engine, you probably won't hear the '03. Torque remains at 460 lb-ft (at 1400 rpm), and horsepower is up slightly to 250 (at 2900 rpm), with another 100-200 useable rpm added to the top end. California emissions mean its market gets the same 235/460 rating as last year, an exhaust catalyst, and no high-output option (Cummins is working diligently on this and hopes to offer an H.O. for 50 states). Gearboxes for the diesel are five- or six-speed manuals and the same four-speed automatic from last year.
The High Output Cummins is now rated at 305 hp (at 2900) and 555 lb-ft (at 1400). This ranks slightly behind Ford's new 6.0L PowerStroke for hp (325 anticipated), but betters both the competition's larger V-8 engines for torque and delivers 400-600 rpm lower in the rev band. The common-rail injection also helps in low end, with torque at 1000 rpm up by 20 percent and clutch engagement torque (already over 300 lb-ft) up 10 percent. We expect fuel economy to be up ever-so-slightly in the standard diesel and about the same with the H.O.; the truck is heavier but more aerodynamic, and the standard axle ratio is 3.73:1 (shorter than previous Rams' 3.55:1) with 4.10:1 optional. Engine serviceability with any powerplant is slightly tighter than the previous model, but filter locations have been carefully considered.
These gears run in all-new axles, too, with American Axle supplying the full-floating rear-ends of 10.5- and 11.5-in. ring gear sizes. The optional limited-slip unit is a helical-gear design, not a clutch pack, meaning less chatter, less decline in performance over time, and no special lubricant modifier requirements. In 4WDs, the front axle carries as much weight as before, but it uses a smaller 9.2-in. ring gear than the previous Dana 60 axle. More significant, there's no axle-disconnect system, so the front end is always turning and engaging front drive is easier. Fewer moving parts simplify servicing, and the aftermarket is no doubt working on a manual locking hub conversion already. An electrically shifted NVG273 transfer case is available on some models, with a lever-operated unit standard.