Born to Run
Paccar launches an engine for Class 8 Kenworths and Peterbilts
By David Kolman
Paccar recently introduced the MX, a 12.9-liter, six-cylinder engine that will be standard in heavy duty North American Kenworth and Peterbilt trucks starting this summer. Able to work with all types of transmissions, the engine is available with a horsepower range of 380 to 485 and torque outputs from 1,450 to 1,750 pound-feet. An integral engine compression brake provides 460 braking horsepower at 2,200 rpm, which Paccar says is
15 percent more than the nearest competitor.
The MX uses four valves per cylinder and an in-block cam design and incorporates a number of advanced design and component integration features. High-strength compacted graphite iron (CGI) is used in the engine block and cylinder head. This material is stronger (75 percent) and lighter (20 percent) than conventional grey iron, resulting in “superior power-to-weight performance.”
There is a single camshaft, and crankshafts have no counterweights — reducing weight by 25 pounds and increasing power for quicker acceleration and smoother overall operation.
Fractured cap technology, introduced by Paccar in 2006, is used for connecting rods and main bearing caps. The technique produces a rough irregular mating surface that forms when the bearing cap is physically fractured from the rod, virtually eliminating cap shift. This contributes to longer power and torque curves along a wide rpm range.
The fracturing process saves machining steps and provides more precise crankshaft-bearing geometry than does conventional hot forging, a procedure in which rods are sawed in two.
The MX’s block design, rear geartrain and floating oil pan contribute to significantly reduced vibration and lower in-cab noise levels, resulting in a more comfortable driver environment. Paccar engineers say the engine is two to three times quieter at idle and one and a half times quieter at 55 to 70 mph than competitive engines.
The electronically-controlled high pressure fuel injection system provides precise fuel control, operating at up to 2,500 bar injection pressure (36,750 psi) for optimum combustion efficiency and assisting in achieving the low emissions required by the EPA. Also helping with improved fuel economy are the crankshaft, lubrication system and other internal components designed to lower parasitic energy loss.
While new to this market, more than 125,000 Paccar MX engines are operating in DAF Trucks globally. Paccar boasts that the MX has a B10 engine life of one million miles, meaning 90 percent of the engines will reach that mileage. Other engine manufacturers’ stated durability is B50, with 50 percent of the engines expected to reach one million miles.