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Construction machines are getting bigger in the behind.

As more manufacturers add tailpipe controls to meet new diesel-exhaust rules mandated by the U.S. Environmental Protection Agency, the devices are taking up valuable backside space, manufacturers say.

Speaking last night at the World of Concrete in Las Vegas, George Whitaker, product marketing manager for Case Construction Equipment called it "the Serena Williams effect." The EPA rules went into effect Jan. 1 for off-road diesels rated at greater than 175 horsepower.

Case is displaying two machines at this week's World of Concrete that meet EPA's new Tier 4 exhaust rules. One is its C-Series excavator, which uses cooled exhaust-gas recirculation (EGR) and a diesel-particulate filter (DPF) to cut down emissions.

Fuel efficiency is up as much as 10%, but the machine has a bigger rump than the outgoing model. Engineers had to add about 60 mm of space around the engine to accommodate the DPF and other components, such as larger radiators.

But Whitaker thinks that number is relatively small compared with the competition. "When you see some of the other excavators on the market, you're really going to see some Serena Willamses," he said.

To alleviate safety concerns due to the reduced visibility around the machine, Case is installing a rearview camera as standard equipment.

"It's a precautionary thing to make them safer," said Ion Warner, Case's senior director of marketing. A sideview camera is optional.

While larger machines like this one are rolling out this year with the new tailpipe controls, manufacturers are concerned about how to package the emissions gear into small machines, such as skid-steers.

"There is no doubt that the Tier 4 emissions for many manufacturers is going to require a lot of redesign," said Kevin Coleman, marketing engineer for Caterpillar Inc.'s compact loader line. "There is going to be a lot more junk in the trunk."

The EPA schedule for Tier 4 has smaller machines to cut emissions starting in 2012—machines with engines rated at less than 175 hp will start coming out next January.

Weight Watcher

Case also is showing what is thought to be the first off-road diesel to use on-road scrubber technology at this week's World of Concrete.

The new 721F wheel loader (pictured above) uses selective-catalytic reduction (pictured below) to meet Tier 4 reductions by injecting urea into the tailpipe to neutralize nitrogen-oxides. Since 2010, SCR has become a common way for heavy diesel trucks to meet EPA clean-air regulations.

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Located in a 12.5-gallon tank, the urea is piped into the injector (lower right of the above photo) at a rate of about 7% relative to fuel burned. That means loader operators will have to fill up the urea tank about every other time they refuel, Case says. A catalyst (the shiny cylinder on top) is where the chemical reaction takes place.

Fuel economy is up as much as 17% and the machine will cost, on average, 7% more to buy at retail. But Case engineers were able to pack in the scrubber kit without redesigning the hood of the outgoing model.

Some machines, it seems, can still fit into their skinny jeans.