GM Ponders Reviving 4.5-liter Duramax V-8 Diesel


Last year, General Motors to offer a 4.5-liter V-8 Duramax light-duty diesel engine in its half-ton pickups as the market for personal-use pickup trucks shrank, the U.S. economy nosedived and GM went into survival mode by shedding brands and restructuring.

Now, with signs that truck sales and the economy have turned a corner and GM refocused on its smaller product portfolio, some at GM wonder if the 4.5-liter Duramax could be revived to play a broader role, not just in light-duty pickups but in the automaker’s revamped heavy-duty trucks, too.

“The 4.5-liter V-8 is fully developed and ready,” said Mark Cieslak, GM’s full-size truck chief engineer. “[If we decided to offer it] we could launch it in a heartbeat.”

Also driving the decision to possibly pull the 4.5-liter Duramax off the shelf are tough new EPA fuel economy regulations for light-duty cars and trucks that are being phased in between now and 2016, and a new push to create fuel-efficiency standards for medium-duty and heavy-duty trucks – including pickups over 8,500 pounds gross vehicle weight – that would go into effect starting with the 2014 model year. Medium-duty and heavy-duty trucks aren’t required to carry EPA fuel economy ratings today.

“Fuel economy is top-of-mind in every vehicle discussion we have today inside GM,” Cieslak said. “Every powertrain discussion, we are breathing fuel economy.”

That has GM’s truck team wondering about using the 4.5-liter V-8 in GM’s HD pickups.

“The 4.5-liter V-8 is a legitimate contender for the 2500 segment, but are customers and [the economic environment] ready for it?” said Cieslak and Gary Arvan, Duramax chief engineer.

GM’s newly launched 2011 Chevrolet Silverado and GMC Sierra Heavy Duty pickups feature an updated 6.6-liter LML Duramax V-8 diesel, which GM says is rated a best-in-class power of 397 horsepower and 765 pounds-feet of torque while returning 11 percent greater highway mileage compared with the outgoing LMM model.

The 6.6-liter V-8 can tow up to 21,700 pounds and haul up to 6,635 pounds, but all that power isn’t necessary at the lighter end of the HD market, in the three-quarter-ton 2500 segment.

“[The 4.5-liter Duramax] could get a few miles per gallon more [than the 6.6 Duramax],” Arvan said. “It’s a high-performance diesel with a high level of work capability and fuel economy.”

The 4.5-liter V-8 might be a better choice for those who don’t need maximum capability from an HD pickup but still need a truck that’s tougher than a half-ton. It wouldn’t necessarily be compromise. It’s as strong as HD diesels were just a decade ago and more sophisticated.

“[The 4.5-liter Duramax] would have launched [with power ratings] about where the Duramax was in 2001 when it was introduced,” Arvan said.

Like the all-new 6.7-liter Power Stroke V-8 diesel that Ford introduced in the 2011 F-Series Super Duty lineup, the 4.5-liter Duramax was designed by GM entirely in-house with reversed intake and exhaust relative to a conventional diesel, so fresh air would enter the cylinders from the outer edges of the cylinder heads while exhaust gases would be dumped between the cylinder heads directly into a turbocharger. The design eliminated the intake and exhaust manifolds and other related components, saving weight, reducing size and lowering costs by up to an estimated $600 per engine compared with a conventional diesel. GM promised power ratings for the 4.5-liter Duramax would be more than 310 hp and 520 pounds-feet of torque with up to 25 percent better fuel economy than a comparable gasoline engine.

Even if the 4.5-liter Duramax cost less than the $8,395 6.6-liter Duramax (including Allison 6-speed automatic transmission), it would carry a higher premium over the standard 6.0-liter V-8 in GM’s HD pickups. Offering the 4.5-liter in GM’s light-duty pickup trucks too (as originally intended) might help make the business case that finally brings this engine to market.

What do you think? Would you opt for a lower rated, more fuel-efficient engine in your heavy-duty pickup?


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