International Truck and Engine Corp., Navistar International Corp.'s long-time diesel engine and commercial truck maker, will introduce next year an all-new line of “big-bore” diesel engines for heavy-duty trucks that use compacted graphite iron (CGI), an advanced iron formula that is stronger, yet demonstrably lighter than the conventional gray iron from which most diesel engine blocks are cast.

International's move is another boost for CGI, whose proponents have spent years expounding its weight-saving advantages for diesel engines for the passenger-vehicle market, as well.

International engineers say it is difficult to gauge precisely how much weight CGI will shave from its all-new line of Maxxforce big-bore diesel engines, but a typical engine in the 11L to 13L big-bore range weighs on the order of 2,500 lbs. (1,135 kg).

It is expected there will be “a couple hundred pounds saved over a conventional gray iron construction,” says Tim Shick, director of marketing-International Big-Bore Engine Business.

Shick and Jacob Thomas, International's vice president-Big-Bore Engine Business, say the new, CGI-intensive Maxxforce big-bore diesels are the first product of a strategic agreement between International and Germany's MAN Nutzfahrzeuge AG to collaborate on design, development, sourcing and manufacturing of commercial-truck diesels.

“Our plan is to bring this engine to market at full production levels in October 2007,” says Thomas.

The new Maxxforce big-bore diesels spearhead the company's first foray into the 11L-13L commercial-diesel segment. To now, International's Class 8 trucks have used big-bore diesels sourced from Caterpillar Inc. and Cummins Inc.

In addition, International launched an all-new Class 8 truck range, ProStar, this spring, with advanced aerodynamics that the company promises will deliver best-in-class fuel economy.

And when the new CGI-intensive Maxxforce big-bore diesels become available next year, they will be offered exclusively in the ProStar trucks.

“We think it's going to recalibrate the industry,” Shick says of the combination of CGI big-bore diesels and the company's aerodynamic ProStar Class 8 haulers.

He says the use of CGI for the big-bore engines' cylinder blocks is intended to deliver fuel economy and noise, vibration and harshness (NVH) improvements. Because CGI is 40% stiffer than gray iron and has 75% better tensile performance, the increased robustness allows the engine to use higher fuel-injection and cylinder pressures — both of which enhance economy and cut emissions.

The design and basic architecture of the new common-rail, direct-injection diesels' block and heads come from MAN, says Shick.

But he adds, “The North American version is much more advanced” than that made by MAN for the European market.

The CGI formula is achieved by adding a measured amount of magnesium to the base iron compound prior to casting. This precision process creates a microstructural composition that, because of the way the magnesium is aligned, is much harder and resistant to stress cracks than are gray and nodular iron, which also contain magnesium in less-robust structural patterns.

The Swedish company SinterCast AB provides the process-control equipment and expertise used by almost all iron foundries that have installed CGI capability.

In the auto industry, CGI also has been making recent inroads. Ford Motor Co. is believed to be the highest-volume manufacturer of diesels with CGI blocks, building upwards of 150,000 units at its Dagenham, U.K., engine plant.

The Volkswagen Group employs CGI for its V-6 and V-8 turbodiesels.

Because of its hardness, the primary liability for CGI's use in the auto industry has been developing tooling to machine the material. Ford says it worked for nearly eight years to develop processes and tooling to machine CGI in high volumes.

“A lot of advances have been made in machining of CGI,” notes International's Jim Thomas, saying the company's partnership with MAN also helped to develop the tooling to machine CGI in volumes necessary for the heavy-truck industry.