Stopping
power was adequate for the payload, but we’ve got a gripe that GM
needs to equip these trucks with larger diameter disc brakes.
At 12.8-inches
front and rear, they’re smaller than the standard 13.9(!) and 13.6-inch
discs on the all new light duty 2007
Toyota Tundra. We’d like some extra meat for this barbecue if
we’re going to be pushing payload limits and need to brake suddenly.
GM offers
two distinct dashboards for its new pickups.
The Sierra,
clothed in SLE trim, featured the “pure pickup” interior that
traditionalists like us love. It’s what a truck dash should be.
Functional with large buttons and great ergonomics, the recessed and silver
bezzeled analog instruments look terrific and instantly provide the driver
with critical information from trailering braking power levels to fuel
economy. The texture and grain of the truck dash is much better than the
800s. Gaps are crazy tight. Clearly Bob Lutz’s attention to vehicle
interiors has been heard and buyers are going to be rewarded even on the
Work Truck level trim.
Truck number
two was a Sierra 3500HD single rear wheel crew cab long box equipped with
a Duramax diesel. With an empty bed, it was an oil burning hot rod.
The latest
edition of the proven Duramax is the 6.6-liter V8 LMM. Like the 2007 Ford
Super Duty's Powerstroke and the Dodge Ram's Cummins, this diesel is pushing
the envelope when it comes to performance and emissions.
January 1,
2007 the federal government ratcheted up emissions rules for diesel engines
to reduce particulate emissions by 90% and nitrogen oxide output by 50%.
The feds also mandated the sale of ultra low sulfur diesel (ULSD), which
reduced sulfur content in diesel fuel from 500 ppm to 15 ppm.
To meet
the tough new rules, the LMM differs from the previous
LBZ version by adding a complex diesel particulate filter (DPF) to
scrub the exhaust gases and a larger exhaust gas recirculation (EGR) cooler
to lower cylinder temperatures and reduce nitrogen oxide during combustion.
The new DPF
system is particularly interesting. It’s a “regenerating”
multi-stage filter that passes engine exhaust into a ceramic, honeycombed
block, trapping the particulates after they’ve passed through an
oxidizing catalyst. Sensors before and after the emissions system tell
the DPF when there's too much back pressure from the soot load. To clean
the filter the engine temperature is briefly raised to 1,022 degrees Fahrenheit
to incinerate the trapped particles, thus regenerating the system for
another round of filtering.
While great
for emissions, if you regenerate immediately after a fuel stop, you’re
going to be disappointed with the fuel economy even though overall fuel
economy for the LMM is expected to be slightly better than the LBZ.
