LAS VEGAS - Navistar International will follow a "build and hold" strategy as it rolls out the first SCR-equipped MaxxForce 13 diesels, beginning in April.

The 12.4-liter MaxxForce 13 will use SCR aftertreatment equipment purchased from Cummins Emissions Solutions. Its various ratings will be calibrated to work with the new-to-Navistar equipment, and it may take several programmings before the calibrations are final, said Steve Gilligan, vice president of product marketing, during a briefing for reporters at the American Trucking Associations Management Conference & Expo in Las Vegas.

"Recalibrations are a fact of life" for modern diesels' electronic control systems, he said, and work on the new engines should be complete by the end of 2013.

Navistar so far has built "a handful, maybe six" MaxxForce 13s with SCR, and will assemble another 40 in November, Gilligan said. These will undergo the testing and validation before they're released to customers.

Exhaust systems will use an oxidation catalyst and a diesel particulate filter, as now, plus a urea injection chamber that's the active part of SCR. Diesel exhaust fluid will be carried in special tanks, as they are on competitors' trucks since early 2010.

Exhaust systems on International tractors and trucks will be available in four configurations:

- "switchback," with components packaged in a cube and mounted beneath the passenger side of a cab;
- vertical-vertical, where they're stacked behind the cab and gases exit through a vertical stack;
- horizontal-horizontal, where all parts are hung from the main frame; and
- horizontal-vertical, with components hung on the frame and exhaust gas exits through a vertical tailpipe.

MaxxForce 13s will first go into ProStar+ and LoneStar highway tractors and WorkStar vocational trucks, then later in TranStar regional tractors, Gilligan said. The Cummins ISX15, which has used SCR since January 2010, will initially be available in the ProStar+, then in other heavy models when it is released in January.

Navistar has enough EPA emissions credits to continue producing medium-duty diesels without SCR through 2013 and into 2014, he said.