Noise Testing
Diesel engines have a bad reputation for being noisy, but the new 6.4L Power Stroke was designed to be the quietest oil-burner ever sold by Ford. It uses fast-acting piezo electric injectors and high-pressure, common-rail fueling to deliver multiple precise shots of fuel for smooth and quiet injection events. Placement of the injectors under the valve covers and insulation in the engine compartment combat noise from the diesel, along with exhaust tones being chopped up by two turbos. Even with these advancements, the diesel is noticeably louder at idle than the overhead-camshaft, V-10 gas engine. The diesel was a bit quieter at wide-open throttle and while driving on the highway at 65 mph; both trucks scored the same while cruising at 40 mph. While measuring the diesel, it went into its Active Regeneration soot-burn cycle, where engine rpm and post injections are used to increase EGT and cook matter trapped in the diesel particulate filter. Surprisingly, the higher engine speed smoothed out vibrations and quieted the cabin by 2 dB.
6.4L, V-8 Power Stroke diesel
Interior at idle: 70 dB (68 dB during Active Regeneration)40-mph cruise: 82 dB65-mph cruise: 83 dBWide-open throttle: 85 dBOpen-hood idle: 81 dB (86 dB during Active Regeneration)
6.8L, V-10 Triton gasoline
Interior at idle: 61 dB40-mph cruise: 82 dB65-mph cruse: 85 dBWide-open throttle: 88 dBOpen-hood idle: 77 dB
 An aluminum rear differential...  An aluminum rear differential cover is used on the diesel trucks to keep the gears cool when the Power Stroke is sending 650 lb-ft of torque through the drivetrain. |  The diesel-engine package...  The diesel-engine package takes up every square inch of the engine bay, and multiple radiators make sure there is no spare room behind the grille. |  We counted six coolers including...  We counted six coolers including the air-to-air intercooler, A/C condenser, coolers for the high-pressure fuel system/variable turbo actuator, transmission, power steering, and engine coolant. |
After Driving Both TrucksWould You Pay $6,895 More For The Diesel Option?
Twenty years ago, I can remember daydreaming about buying an '87 F-350 with a 460ci, big-block gas engine. At the time, I had no interest in the 351ci small-block or the 6.9L diesel because I wanted all the horsepower Ford would sell me. My, how times have changed.
I knew going into this test that if Ford's V-10 Super Duty was even close to being as powerful and fuel-efficient as the 6.4L Power Stroke, we'd all be in trouble. Sure, we're biased toward the diesel engine because we write for Diesel Power magazine, but on paper, the 362hp V-10 looks like it should do everything the 350hp 6.4L diesel can-especially when optioned with the 4.30 axle gears (compared with the diesel's 3.73s) our test truck had. I'm pleased to report that when it comes to towing, acceleration, and fuel economy, the gas engine doesn't even come close.
When driving the two trucks back-to-back, the biggest difference I noticed was how much lighter (and somehow smaller) the V-10 truck felt. The V-10 does have better throttle response than the diesel, and after driving it, I would have sworn it was quicker than the 6.4L. I think the dragstrip numbers we recorded favor the diesel because we were able to spool both its turbos before launch. In a traffic-light drag race, the two trucks may be a closer match than our data show.
The 6.4L Power Stroke definitely felt more powerful overall, which is great for our job security. The torque advantage is impressive when towing or just cruising up grades at highway speeds. I was also pleased to see the diesel's fuel-economy advantage still shines through all the new emissions equipment. It remains to be seen how the aftermarket is going to modify these trucks, but I have no doubt we'll see 100hp upgrades by the end of the year.
Would I pay $8,385 for the diesel/automatic options? Without a doubt, I would. I think if you're in the market for a truck this size, the diesel engine just makes more sense. Ford puts more engineering resources into the diesel, the Torqshift transmission gear ratios are better suited to the diesel's power curve, and the diesel truck's resale value is higher. The days of the big-block gas engine are truly over.-David Kennedy, Editor
At first, $6,895 sounds like a lot of money. Add $1,490 onto that for an automatic transmission (the only thing I'd want behind a turbodiesel), and you've got $8,385-almost enough to make you consider a life with spark plugs. Thoughts like that are caused by sticker shock, and the only cure is to get behind the wheel of the dream truck that's haunting your wallet and see if it feels worth the extra cash, and the 6.4L Power Stroke diesel passes that test.
It's quiet but performs like a hot rod. When both turbos are spooled, it feels like the Super Duty should be wearing an SVT badge on the tailgate. The only bummer is the sluggish operation of the electronic throttle control when aggressive inputs are received from your right foot, even though there's almost always 20 psi or more of boost on tap. It's no surprise because the 6.4L Power Stroke has to produce 650 lb-ft of torque while emitting no black smoke and getting good fuel mileage. This is achieved through a slow build of fueling after you mash the pedal that only seems to peak right before it's cut off in preparation for the First-to-Second-gear shift. Full fuel is available (except during shifts) until the truck reaches 86 mph when the speed limiter kicks in.
The V-10 gas truck does not suffer from a very noticeable lag between input and power delivery, but it's a lot easier to make gasoline burn clean when EFI and 10 relatively small cylinders are used. Thanks to less torque, the gas Super Duty doesn't cut power very much between shifts except when the transmission is cold, so it's easy to play with the truck's entire powerband.
After driving both trucks on the same mountain routes and dodging through city traffic, I noticed the diesel's lag (don't call it turbo lag, though) faded into the background. Both of these 31/44-ton trucks can be squirted through lane changes and up steep grades with ease, but the diesel always has more power in reserve, especially while towing. Add in much better fuel economy and the fun factor of a chipped truck, and it would seem foolish to choose the gas V-10 when the new dual-turbo, 6.4L Power Stroke is available-even if the diesel/automatic option costs $386 more than a Kawasaki Jet Ski STX-12F.-Trevor Reed, Feature Editor
From a purely monetary standpoint, the difference in Fuel mileage alone will save you $7,000 with the diesel after only about 50,000 miles of driving if diesel and gas both stay at around $3 a gallon. Diesels also hold their resale value better than gas vehicles, and they last longer. The diesel makes sense.
As far as driving impressions go, the gas truck had great throttle response and had a broad powerband all the way up to 5,000 rpm, which was surprising when considering the engine's size. Once I climbed into the diesel, however, it felt like a rocket ship, with power available at virtually any rpm in any gear once the turbos were spooled up. The only downside was the diesel still had lag from a dead stop, but other than that, throttle response was good, even at low speeds.
Would I pay the extra money and buy the diesel? You bet. The only situation in which I would choose the gas truck over the diesel would be zipping in and out of city traffic. In all other situations-freeway driving, accelerating, and towing-I feel the diesel is the better choice.-Jason Sands, Associate Editor