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Diesel Army often gets questions from our readers and fans wanting to know the difference between the diesel truck offerings from the “big three” in regards to engines and transmissions. With this in mind, we put ourselves to the task of talking directly with the manufacturers and really getting down to the “nitty gritty” to bring our readers all of the in-depth specifics needed to make a more informed buying decision when shopping for your particular needs.

GM (Chevrolet Silverado and GMC Sierra)

With a new redesign being released for the 2014 model year, the new Silverado and Sierra models are going to be hot commodities. The 2014 Silverado HD lineup will continue to be offered in WT, LT and LTZ models as 2wd or 4wd, including single and dual rear wheel 3500HD models. All feature fully-boxed, high-strength steel frames and offer an array of control features that make hauling and towing easier, including trailer sway control, integrated brake assist and larger brakes.

2014 Chevrolet Silverado 3500 HD LT Crew Cab Pickup

In addition, the Silverado HDs will still offer a smart exhaust brake feature that provides greater control on grades and reduced brake pad wear. For the new features, most of them are going to be interior and exterior design and option changes that we will cover in an upcoming review when the trucks hit the showroom floor. New for 2014 is an optional spray-on bed liner. While it is an extremely common practice for dealers to send trucks out to have “spray in” bed liners installed, now – this will be a factory option, which means factory quality, warranty, and good looks.

On the powertrain side of things, not much appears to be changing. However, the optional 6.6 Duramax can still be mated with an Allison 1000 6-speed automatic. The power ratings and emission controls remain unchanged as well. As a result, the capabilities of the new 2014 appear to be mostly unchanged over the 2013 model year (however, things could change when they hit showrooms with a few surprises).

Ram (2500 and 3500)

2013 Ram 3500 Heavy Duty

Coming off a refresh in 2013, the 2014 Rams won’t see many changes. The 2500 HD chassis has gone through a complete redesign, offering a five-link coil design that provides better articulation than a standard leaf spring system. The 2500s have an optional air ride system that replaces the coil with airbags, giving the truck a much softer ride while not sacrificing capability.

In addition, the air suspension has an automatic load leveling capability, which helps to improve stability and the ride when loaded. On the 3500s, the optional air system is available as an air assist to the Hotchkiss leaf springs. Up front, the three-link suspension offers greater roll stiffness over previous generations and all of the connections are larger and stronger for increased capability.

For the powertrain, it’s hard to argue with a proven combination. The 6.7 Cummins has three transmissions ranging from the old proven 6-speed manual to the high tech AISIN 6-speed automatic. With the addition of Diesel Exhaust Fluid (DEF) in 2013, the 6.7 remains mostly unchanged and still one of the powerhouses of the automotive industry.

Ford (Super Duty – Excluding F-450)

2013 Ford F-Series Super Duty Platinum

Introduced in 2011, the Super Duty remains pretty much unchanged. There are some styling changes that will be covered in a future new vehicle review. However, the major focus for the engineers at Ford was to improve braking. The engineers were able to increase the front braking area by 16.4 percent and rear by 14.5 percent. These changes lead to an increase in the gross vehicle weight rating (GVW).

On the powertrain side of things, everything is mostly the same as well. After recently going through two major emission changes and three engine offerings (finally manufacturing and designing the last engine offering in house) Ford is holding firm on what they currently have in place. The 6.7 Power Stroke with the Torqshift transmission remains prominent.

Engine Specs From The Big 3:

GM Offerings

In recent years there have been two major emission level requirement changes that manufacturers have had to overcome. With Ford and Dodge both having to increase the displacement of their engines to achieve the emissions requirements, it’s amazing that the Duramax has remained a 6.6L since its inception back in 2001.

GM - 6.6 Duramax (LML)

2013 Duramax 6.6L V-8 Turbo Diesel (LML) for Chevrolet Silverado HD

  • Engine: 6.6L Duramax V8
  • Turbo System: Single with variable geometry
  • Head Material: Aluminum-alloy
  • Block Material: Cast Iron
  • Bore: 4.05 inches
  • Stroke: 3.89 inches
  • Horsepower: 397 hp at 3,000 rpm
  • Torque: 765 lb-ft at 1,600 rpm

Since 2001, there have been 5 revisions LB7 (2001-2004), LLY (2004-2006), LBZ (2006-2007), LMM (2007-2010), LML (2011-present) but no displacement increase. The LML has all of the emissions bells and whistles these days, including Exhaust Gas Recirculation (EGR), Diesel Particulate Filter (DPF), Diesel Oxidation Catalyst (DOC), Selective Catalytic Reduction (SCR), and Diesel Exhaust Fluid (DEF).

On the fuel side of things, a Bosch CP3 fuel pump produces up to 30,000 psi to the two common fuel rails. Injecting the fuel into the engine is handled by Bosch Piezo Electric Injectors that are able to fire multiple times per combustion cycle. A Garrett single Variable Geometry Turbocharger (VGT) handles supplying the air to the engine.

Internally, the cast aluminum pistons have been shaped to create a compression ratio of 16:1. To assist in cold weather starting, the Duramax employs glow plugs. All of the LML engines are rated to run up to 20 percent bio diesel (B20) and the engines are rated to produce 397 horsepower at 3000 rpm. This is only 3 horsepower less than Power Stroke but 47 more than the base model Cummins.

When comparing the torque side of the equation, the Duramax comes up slightly short against the high output Cummins, but is 105 lb-ft higher than the base. 765 lb-ft of torque at 1600 rpm is extremely respectable, but slightly lower than the Power Stroke as well.

Dodge Offerings

Dodge - 6.7 Cummins

cummins

  • Engine: Cummins 6.7L inline-six
  • Turbo: Single with variable nozzle
  • Head Material: Aluminum-alloy
  • Block Material: Cast iron
  • Bore: 4.21 inches
  • Stroke: 4.88 inches
  • High Output Horsepower: 385 hp at 2,800 rpm
  • High Output Torque: 850 lb-ft at 1,600 rpm
  • Base Auto Horsepower: 370 hp at 2,800 rpm 
  • Base Auto Torque: 800 lb-ft at 1,600 rpm
  • Manual Horsepower: 350 hp at 2,800 rpm
  • Manual Torque: 660 lb-ft at 1,500 rpm

The Cummins engine has been a staple in the light duty diesel industry almost since its inception. The same basic engine configuration has maintained in the Dodge/RAM trucks from 1989 to present with the exception of a displacement increase in 2007. There have been 4 major revisions commonly referred to as: the 12-valve (1989-1997), 24-valve (1998-2002), Common (2003-2007) and finally the 6.7 (2007 to present).

As with the other engine manufacturers, the 6.7 equipped truck has the full host of emissions components such as EGR, DPF, DOC, SCR and DEF. Of these, the SCR and DEF were the new additions in 2013. Prior to 2013, the engines were able to meet emissions requirements without it, but as horsepower and torque increased, so did the amount of emissions equipment required.

To provide fuel, the 6.7 uses a Bosch CP3 fuel pump to pressurize a single common rail. The rail feeds the 6 injectors, which are Bosch Piezo Electric Injectors that are able to fire multiple times per combustion cycle. The fuel system has been designed to handle up to 20 percent bio-diesel. To supply the air to burn the fuel, a Holset Variable Nozzle Turbo (VNT) single turbocharger is used. A benefit to the VNT, is the fact that RAM can change the nozzle and increase back pressure during long downhill runs, which provides, exceptional engine braking.

A really cool feature of the Cummins equipped trucks is the Ram Active Air intake system. The Active Air system can sense high outside temperatures and switch the path of the air intake from an under-hood inlet to an inlet that is close to the grille. When the vehicle senses rain or snowy conditions, the air intake system switches back to the under-hood inlet to keep water and snow away from the intake system.

For the 2014 model year, there are three versions of the 6.7 available. For the 6-speed manual guys, the 6.7 has a rating of 350 horsepower at 2,800 rpm (up 50 horsepower) and 660 lb-ft of torque at 1,500 rpm. The next step up is the 68RFE 6-speed automatic. The engine rating for this transmission is 370 horsepower at 2,800 rpm and 800 lb-ft of torque. This falls right in line with Ford and GM. The 370 horsepower is slightly lower than both the Duramax and Power Stroke but the 800 lb-ft of torque is more than the Duramax and ties the Power Stroke.

To get the High Output Cummins, you have to step up to the 3500 and pick up the AISIN 6-speed automatic. From there, the 6.7 HO is the king of the road with an impressive 850 lb-ft of torque at 1,600 rpm and 385 horsepower at 2,800 rpm. This is one “bad mother” with it’s torque being unmatched by anyone and the horsepower only 15 off of Ford’s 6.7. This combination is an impressive offering and the fact that it was done under the heaviest emissions regulations yet, is even more impressive.

Ford Offerings

Ford - 6.7 Power Stroke

6.7-Liter Power Stroke(R) V-8 Turbocharged Diesel Engine

  • Engine: 6.7L Power Stroke V-8
  • Turbo System: Single sequential with variable geometry
  • Head Material: Aluminum-alloy
  • Block Material: Compacted graphite iron
  • Bore: 3.90 inches
  • Stroke: 4.25 inches
  • Horsepower: 400 hp at 2,800 rpm
  • Torque: 800 lb-ft at 1,600 rpm

The 6.7 Power Stroke marks a major new chapter in Ford’s book. After decades of relying on the quality and durability of an outside supplier’s engine, Ford decided it was time to bring the engine development in-house. Since that decision in 2011, they haven’t looked back. The warranty issues are well under control, consumer support and confidence has risen, and there is an overall sense of pride back at the blue oval dug out.

The new engine features many revolutionary developments – the most significant is the design of the cylinder heads. When Ford designed the 6.7 Power Stroke, they kept it as a V-8 (Ford has offered a V-8 diesel since 1982) but they took a hard look at how the engine works. Since the engine is a V-8 and they use a turbocharger, which sits on the engine valley, it doesn’t make sense to send the exhaust out the outside of the engine, then route it back up to the top of the engine. It makes more sense to have the exhaust exit the engine in the valley right where they need it. Then send the cool, fresh air to the outside of the engine.

This is how their reverse flow cylinder head functions and by the numbers, it’s working pretty well. This is also the first engine to use a factory air to water intercooler. This keeps the packaging tight, and improves throttle response. To aid throttle response even more, Ford teamed up with Garrett to produce a DualBoost turbocharger. This turbocharger is a variable vein turbo that features two compressor wheels (one wheel with a different profile on each side). This combination allows the boost to come on quickly while supporting the airflow requirements needed for top-end power. With this being a clean sheet approach, Ford was able to really create what we think will be considered a revolutionary engine package for the diesel market.

The Power Stroke uses a Bosch CP4.2 high-pressure fuel pump to run up to 30,000 psi of injection pressure through Bosch Piezo Electric Injectors. The engine does have the same host of emissions controls as the other engines: EGR, DPF, DOC, SCR and DEF. In addition, it too is B20 capable. Since about six months after being introduced, the 6.7 Power Stroke has been the horsepower leader laying down 400 horsepower at 2,800 rpm and 800 lb-ft of torque at 1,600 rpm. The 400 horsepower reigns’ supreme and the 800 lb-ft of torque are only out done by the 6.7 High Output Cummins.

Having power is one thing, transferring it back is quite another when it comes to Diesels.

How The Game Is Won Or Lost // Transmissions And Differentials

GM Chevrolet/GMC

AllisonThe Allison transmission has been one of the hallmarks of the Duramax option. Being the only transmission currently available for the Duramax, means it must be rugged enough to handle everything the different truck options can handle. Its current 6-speed gear ratios are: 1st-3.10, 2nd-1.81, 3rd-1.41, 4th-1.00, 5th-0.71, and 6th-0.61 with a final drive ratio of 3.73:1 in the rear.

With a double overdrive and a 3.73:1 rearend gear ratio, the Duramax is still able to achieve good highway fuel economy. Of course if you are reading this, you may already know that there is no mandate to publish fuel economy numbers for these trucks. So, it is really difficult to have a true apples to apples comparison on the MPG front.

With this combination the maximum rated trailer towing (5th wheel) is 17,800 pounds for the regular cab long bed. As a crew cab short bed, the rating drops slightly to 17,400 pounds.

RAM

AisinDodge trucks are the only truck in this segment that has had a higher preferential rating on the manual transmission than the automatic. This speaks to the use of the truck as well as the horsepower rating difference between a manual and an automatic. In recent years, the Ram trucks (Ram became its own brand in 2010) automatic has been beefed up and today, it actually has a higher horsepower and torque rating than the manual option.

The 6-speed manual transmission has the following gear ratios: 1st-5.94, 2nd-3.28, 3rd-1.98, 4th-1.31, 5th-1.00, and 6th-.074. The axle ratio is 3.42:1 for single rear wheels and 3.73 for dual rear wheels.

In a regular cab, long bed configuration, the manual equipped trucks have a maximum tow rating of 18,520 pounds and the crew cabs are rated at 16,850 pounds.

The 68RFE transmission with the higher horsepower and torque rating has the following gear ratios: 1st-3.23, 2nd-1.84, 3rd-1.41, 4th-1.00, 5th-0.82, and 6th-0.63. The axle ratio for a single rear wheel is 3.42, but there are two options for the dual rear wheel trucks: 3.73:1 and 4.10:1.

As the standard automatic option for both the 2500 and 3500 Rams, there is a slight tow rating difference due to the truck’s capability. The 2500s carry an 18,300 pound rating where the 3500s are able to handle 22,560 pounds in a regular cab long bed configuration. As a crew cab the ratings are a little backwards. The 2500 has a rating of 17,900 pounds, but the 3500 is rated lower at 17,500 pounds.

Finally, the big “bad boy” for Ram, the Aisin 6-speed automatic. This tranny is able to hold up to 850 lb-ft of torque and tow up to 30,010 pounds (yes, you read that right). Which is obviously asking for a lot out of any transmission. To achieve that, the Aisin uses the following gear ratios: 1st-3.75, 2nd-2.0, 3rd-1.34, 4th-1.00, 5th-0.77, and 6th-0.63. The rear gear ratios are the same as the 68RFE at 3.42:1, 3.73:1, and 4.10:1.

Ford

2011 Ford F-Series Super DutyMuch like the GM, Ford has opted to only offer the Power Stroke with the Torqshift transmission. Recently overhauled to be mated with the 6.7, the Torqshift 6R140 is a 6-speed with the following gear ratios: 1st-3.97, 2nd-2.31, 3rd-1.51, 4th-1.14, 5th-0.85, and 6th-0.67. The axle ratio comes in a whole host of options from 3.31:1, 3.55:1, and 3.73:1.

When it comes to towing, the maximum rated truck configuration is the regular cab long bed. The dual rear wheel F-350 can tow up to 23,200 pounds while the F-250 is able to tow up to 16,800 pounds. In the crew cab configuration, the F-250 drops slightly down to 16,300 pounds and the F-350 goes down to 22,600 pounds.

Now – Let’s Talk Price

According to the manufacturers and KBB.com, the Duramax with the Allison transmission will set you back an extra $8,395 (MSRP) on top of the standard sticker price. The Cummins with the 6-speed manual is the best-priced option coming in optioned at $7,995. If you select the 68RFE, it will set you back another $500 but the “big dog” AISIN is another $2,650 for a grand total of $10,445. Making it an option really aimed at those who make their living towing heavy loads. For the Power Stroke, the engine transmission option is $8,095 but there are additional accessories that need to be changed so the actual cost sits right at $8,315.

Now that you know the in’s and the out’s of the engines and transmission offerings from the “Big 3” it’s time to to choose the one that best suits your needs. Carefully weigh your options, what you will use the truck for, and your budget (of course) and make your decision – get to work! We would love to hear your thoughts on which one is best for you and why – so please discuss below in our comments section.