Comprehensive changes for GM

GENERAL Motors' 2011 HD Silverado/Sierra trucks have a revised Duramax 6.6-liter twin-turbocharged diesel V-8 — now producing 397 hp and 765 lb-ft of torque — along with a completely new frame and suspension.

GM engineers estimate the 2011 Duramax to be 11% more fuel efficient than before, and it also can now run on B20 biodiesel.

“It's been a great year this year, launching these trucks into the market,” said Dan Tigges, product manager for full size trucks. “We've been getting very positive feedback from the media and our first customers in the market. We have a winner on our hands.”

Virtually every part of the chassis has been upgraded, with only the two front swaybar end links common in the 2010 and 2011 trucks.

The fully boxed frame and suspension upgrades give the trucks payload of up to 6635 lbs and maximum trailer towing of up to 21,700 lbs for fifthwheel trailers and 17,000 lbs for trailers pulled with receiver hitches.

In addition, all four-wheel-drive GMC trucks can now be equipped with snowplows.

The crew cab chassis cab (C/K31043) with 60" CA replaces the extended cab chassis cab, and there is a one-ton crew cab standard 6.5' box SRW (C/K30743). All one-ton trucks used to come with an 8' box. A one-ton two-wheel-drive regular cab (C30903) is now available with single and dual rear-wheel models, a gas engine is available with the pickup box, and gas and diesel engines are available on box deletes.

“The most important changes made on these vehicles were the front suspensions,” Tigges said. “We knew we had to increase capability. People want to move bigger loads, tow bigger trailers, use bigger snowplows than they ever did in the past. In this day and age, 4,800 pounds simply is not enough.”

The gross front axle weight rating (FGAWR) has been increased to 6,000 lbs, with an independent front axle (not a solid front axle) that Tigges said provides significant ride and handling advantages, lower unsprung weight, and a larger tire patch on road.

The rear gross axle weight rating (RGAWR) has been increased to 9,759 lbs. Asymmetric rear leaf springs reduce power hop.

Gross vehicle weight ratings (GVWR) have increased on the 2500HD from 9200 lbs to 10,000; on the 3500HD from 9900 to 11,600; on the 3500HD DRW PU from 11,400 to 13,000; and on the chassis cab from 12,000 to 13,200. Maximum payloads: ¾-ton pickup, up to 4,192 lbs; one-ton pickup, up to 6,635 lbs; and chassis cab, up to 7,293 lbs.

Trailering also has been upgraded, with gross combination weight ratings (GCWRs) on the diesel dual-rear-wheel pickup going from 23,500 lbs to 29,200 lbs; on the diesel DRW ZW9s from 23,500 to 27,500; on the diesel single rear wheel model 22,000 to 24,500; and on gas from 18,500 to 20,500.

Tigges said the 6.6L Duramax Diesel has proven durability and reliability, with over 1.3 million sold since its 2000 introduction, an Allison transmission, and five-year/100,000-mile powertrain warranty.

He said there is improved noise/vibration/harshness (NVH), with high-load/high-speed noise reduced nearly 30%.

The SCR NOx reduction system has been optimized for fuel economy. The Diesel Particulate Filter regen cycle has been lengthened by 75%, with new calibrations reducing soot in DPF and up to 700 miles between regens. It features a lower idle speed, vehicle aerodynamic improvements, and electronic fan clutch, and Allison transmissions improvements.

There are larger fuel tanks: 36 gallons for pickups, 23½ gallons front and 40 gallons rear for chassis cabs, and 63½ gallons for dual.

A diesel exhaust brake is standard on diesel models and utilizes the variable vane geometry turbo to create backpressure on the exhaust to slow the vehicle. Benefits: avoids brake fade due to overheating brakes; improves brake life; improves vehicle control and convenience; and “Smart” control system varies the amount of braking needed for truck, load, and grade.

StabiliTrak is standard on all single rear wheel models (pickups and box deletes). Hill start assist standard holds brake pressure for 1½ seconds to allow transition from brake to throttle and ramps out pressure with throttle apply.

The DEF System features a tank fill neck location under hood on the right side of the engine compartment.

“We really worked to make this system upfitter-friendly,” Tigges said. “It's a location that allowed us to optimize the system so we added a minimal amount of weight. The fill point is under hood, so as an upfitter you never have to worry. It's always the same, whether pickup box delete or chassis cab. And it's out of the way.”

No modifications are recommended, because the DEF system is integral to emissions compliance. DEF lines and hoses should not be moved (they are heated), and exhaust routing modification is allowed after DPF within guidelines published by gmupfitter.com.

Joseph Langhauser, product manager for full-size van and mobility, provided an update on the features of the 2011 Savana and Express. They include six speed transmissions, all-wheel drive (1500 series), diesel engine availability, extra inch of interior space on cutaways, and a 9,156-lb payload rating on the 4500 series — up 106 lbs from 2010.

He said the Duramax diesel engine has 65 lb-ft more torque (now 525 lb-ft) and 10 more horsepower (260 hp) than previous models. The 2011 6.6 Duramax diesel is available on the 3500 passenger vans, with a GVW of 9,900.

CNG a power option

Dedicated CNG systems will be available in Chevy Express and GMC Savana cargo vans, ¾ ton with 135" WB (23405) and 1 ton with 135" WB (33405).

“This is an interesting GM story,” Langhauser said. “Most people think this story started this year. Well, it didn't. We were very lucky. In 1990, we hired a bunch of twenty-something engineers and said we were going to do CNG and LPG in our vehicles directly, and we did. From 1993 to 2003, across four different models, we had CNG and LPG available and installed at the factory.

“In 2000, as we were winding down CNG and LPG, those engineers went off to various spots in the corporation. Fast forward to 2010. Many of those people still existed in the corporation. Now they're fortysomething managers, directors, and executive directors, so not only did they have a strong knowledge about what CNG was all about, but they also had a clear understanding of how the corporation worked, so we were able to figure out a mechanism to not only reintroduce CNG but do it in a very fast manner — something I've never seen in my 25 years in GM.”

The (LC8) Vortec 6.0L V-8 has hardened exhaust valves, hardened intake and exhaust valve seats, dedicated gaseous fuel injection and fuel-storage systems, and is designed to meet EPA and CARB certification.

Under the CNG initiative, it will initially be available in a four-tank, 23-GGE configuration, with a future release having three tanks and 15.8 GGE. The fourth tank is mounted on the cargo floor in an enclosure, inboard of the left rear wheelhouse. There is an effective range of 253 to 368 miles.

CNG and LPG vans will be ordered through Chevrolet and GMC dealers and must include a fleet or government order type. Federal incentives are available to help offset CNG conversion costs. A maximum of $5000 is anticipated at the GVWR and expected emissions level. It's set to expire in December, but could be extended.

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