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2007 Ford Chevy Dodge Diesel Comparison - Big Boost Battlefield

Front View Fire
G. R. Whale | Writer
Posted January 16, 2007
Photographers: Courtesy the Manufacturers

2007 Diesels bring New Peaks to Power Wars

The least powerful 2007 pickup diesel engine delivers 610 lb-ft of torque at 1,400 rpm; if you could load it to full throttle in First gear low and had 4.10:1 gears, it sends better than 40,000 lb-ft to the axleshafts. And with diesel engines getting quieter, you'll have no trouble hearing exactly which U-joint broke first.

A senior GM diesel engineer likens emissions requirements to the tax code, and those emissions changes are what's driving all the upgrades to diesels and the new exhaust after-treatment methods designed for ultra-low-sulfur diesel fuel (ULSD). Although these new standards represent a severe drop, the manufacturers learned long ago that making an engine smaller for any reason doesn't sit well with pickup drivers.

Consequently, none of the Big 3 have lost any power, two of them are larger, and in some areas the exhaust for these trucks will be cleaner than the vast quantities of air they suck in. The smoke is gone and the pipes won't be charred inside: While we appreciate a smokin' diesel as much as the next soot junkie, and fully expect the aftermarket is researching them as we speak, so-called "clean diesels" may help keep the environmentalists at bay and more trails open.

The new lineups are a series of Cummins ISB6.7s for Dodge, a 6.4L Power Stroke, and the Duramax 6.6 for GM. Every one of them uses common-rail fuel injection (maximum injection pressure a bit over 26,000 psi-think of a big pickup sitting on a dime), diesel oxidation catalyst and a diesel particulate filter (DPF-see sidebar), and roughly twice the computing power of last year's engines.

It's been noted on the Web that Cummins' new ISB6.7 shares 40 percent of its parts with the ISB5.9, but all the significant parts-not nuts and bolts but the cylinder head, pistons, crank, turbo, and so on-are new. This is the only '07 pickup diesel that's been bored (5 mm) and stroked (4 mm) for increased volume, but they did it without increasing the length of the engine by removing the water jacket between the cylinders. The extra displacement maintains the low-rpm torque before the turbo spools up, and the extra metal, variable geometry turbo (VGT), EGR (exhaust gas recirculation) cooler, and so forth have added roughly 100 pounds to the engine's weight.

With stroke now up to almost 4.9 inches, there wasn't a lot of room left in the block so the crankshaft counterweights are machined rather than just forged ends, just one of the processes that helps lower NVH levels. Compression ratio is up nearly half a point from that of the 5.9, and the pistons are oil-cooled as before. The basic architecture is much the same and as a result design life-to-overhaul remains 350,000 miles.

Because of different emissions requirements for "commercial" (chassis cab) and "private party" (pickup) use and different ratings, Cummins will supply four CPL (Cummins Parts List, all your Cummins shop needs to know) numbers to Dodge, one each for the chassis cab manual and automatic, and one for each pickup transmission; there are no 49- or 45-state engines. The Chassis Cab is rated lower than the pickup engine primarily because of operating economy, with secondary concerns of cooling, cost, and so on. It's not that a 6.7 can't take a lot of commercial abuse, more a case of how much cooling air can be forced through a Ram grille. Pickup ratings follow the horsepower war that no one will win but GM will lead this year, with automatics matching the Power Stroke and manuals derated to 610 lb-ft to keep the gearbox intact; peak torque on the manual pickup occurs at lower revs than any '07 diesel; and clutch engagement torque of better than 350 lb-ft is unmatched.

Like all the new engines the 6.7 looks more complicated. The first things you'll notice are a slightly lower turbocharger with wires feeding the variable geometry control, a throttle valve and MAP sensor on the intake side (primarily for controlling heat for the DPF regeneration function), and a cooler for the EGR. The Chassis Cab engine has a 14-vane VGT and the later pickup engine a 16-vane, a change related primarily to noise and likely to evolve across the board.

Although common rail systems with up to five injection events per cycle can do a lot for noise abatement, the 6.7 also gets a layered oil pan, a viscous vibration damper, block shields, a "stuffer" between the oil pan and transmission, and an overrunning alternator pulley to quench the shut-down squeaks. The engine is 50 percent quieter than the 5.9 (3 dB lower in the cabin) and you'll be able to hear the difference, especially when parked next to an earlier model.

Since VGT can close the vanes on the turbo, it can to some extent replicate the potato-in-a-pipe effect of an exhaust brake. Dodge is the first to offer a dedicated exhaust brake option from the factory ($300), which gives 190 braking horsepower of retarding effort and is totally integrated with the cruise control and automatic transmission control; a non-optioned truck will still produce retarding effort similar to some earlier-generation Ram diesels equipped with the Mopar Ram Brake exhaust brake. As of this writing, only Chassis Cab models have the options of PTO and 220-amp alternator; prices weren't out yet for the pickup but the Cummins option in a Chassis Cab lists at $5,555-very close to the latest pickup 5.9.

The 2008 Super Duty is first pickup to get sequential turbocharging, a concept already proven on the 4.5L V-6. This is the first Power Stroke with piezo injectors. Packed hardware under Ford hood is typical of V-engine installations. Note the massive cooler pack to support the F-450's commercial-number tow ratings.

As all Power Stroke's preceding it, the 6.4 is built by International Truck and Engine. A slightly larger bore generates the extra volume, meaning some old "390 V-8" badges would be entirely accurate. Although it is derived from the 6.0 Power Stroke, new induction and Siemens injection systems and a host of less significant upgrades make it more than just a 0.030-over punch.

The dual turbochargers are sequential, with the theory proven on the 4.5L V-6 engine that's been powering LCF light-commercial vehicles for more than a year. The turbos are straight oil-cooled units from Borg-Warner, with a small variable-geometry model for fast spool-up feeding the larger unit for peak boost pressures-33 psi at peak torque and up to 42 psi. Ford claims a 0-60 time drop of more than one second, which we assume is empty but is often a traction issue already.

Fuel is now delivered by common-rail injection, except the 6.4 uses piezo injectors. These inject fuel in less than 0.010 second, making it easier to fire precisely over multiple injection events in the same cycle and produce quieter operation, contributing to a claimed 10 dB reduction in noise. However, piezo injectors tend to cost more than conventional solenoid injectors. Like the others, the 6.4 runs up to five events per cycle, with the first post-injection for emissions reduction and the second generally used to light off the DPF regeneration process.

To keep the exhaust cooled, Ford uses louvers in three locations in the 4-inch pipe aft of the DPF to introduce outside air, and dual outlets. The DPF is shielded and does not hang below frame level, where it would limit ground clearance or breakover angle. Although the VGT can supply some engine retarding (estimated at 100 braking horsepower in conjunction with the automatic transmission), it is not referred to as an exhaust brake, and at least one engineer we spoke with said an exhaust brake may interfere with engine emissions performance.

The 6.4 power ratings are the same regardless of transmission, and with more than 95 percent of buyers opting for the automatic, there is the possibility the manual could be dropped for the 2010 model year when another round of emissions changes comes through. Most pickup axle ratios remain the same, but the F-450 brings 4.30:1 to start and up to 4.88:1 for HD hauling (24,000-pound trailer) where you might need a license endorsement. Ford had not announced option pricing at press time.

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