A Grade Flattener

The rolling Texas hill country west of San Antonio is excellent terrain to test the performance of new power units. It is a mix of grades ranging from 3 percent to 7 percent. But there’s also enough flat road to find where the torque curve flattens out and the sweet spot hides.

My drive from Vehicle Testing Services, where Detroit Diesel is testing its VNT EGR (exhaust gas recirculation) for the post-Oct. 1 lower-emissions engines as mandated by the Environmental Protection Agency’s consent degree, also encompasses more than 30 miles of urban interstate driving in heavy traffic. Chuck Blake, Detroit’s application engineer, and Jason Grobbel, the product engineer who runs the Detroit operation at VTS, help me find my way across San Antonio’s tortured interstates, where the 12-liter, 430 horsepower, Series 60 under the Century Class Freightliner hood performs nimbly.

This engine has an almost aggressive throttle response. The nearly silent variable nozzle turbo punches through the rpm range quickly, pulling our 69,000-pound gross weight quite well in 9th and 10th gears. Farther out in the hills, Grobbel confirms my impression: “That quick throttle response gives enough boost to help out a lot on these slow rollers,” he says. And after I stop just west of Kerrville on the last outbound grade, the responsiveness of the turbo is even more helpful getting up to speed on the steep ramp and out into traffic. By the time I reach the top of the grade I had climbed to 8th gear and I coast over the crest without undue water or oil temp rise. Grobbel says Detroit is looking for oil temps to stay below 260 degrees. My gauge reads just about 240 on the most significant pulls.

Blake notes that, “Exhaust temperatures will remain the same even though combustion temps are lower. Engine temps and under hood temps will rise, so cooling is very important. Cooling system maintenance is equally important.” Despite that fact, the same coolants now in use will be standard in Detroit 2002 engines, he says. Oil, on the other hand, will be upgraded to the SAE standard CI-4 level due for introduction this month. New CI-4 oils are formulated to aid in the removal of a heavier load of soot and acids created by EGR engines. Blake also warns that he does not believe all CI-4 oils had been created equal. New owners will want to choose their oils based on specific recommendations and possibly oil analysis.

Just west of Kerrville, I change to the Freightliner FLD that had followed us. In this truck the engine was a Series 60 rated at 500 horsepower and 1650 pounds-feet of torque. Loaded to 78,000 pounds, we manage to flatten all the grades heading east followed closely by the 430. The 7-percent grades took more out of the smaller 430-hp engine I had tested first, but the difference was no more than a drop of one gear, or perhaps a loss of more rpms. At any rate, the 430 stays right behind me all the way back to San Antonio.

Nothing changes my impression about the power, responsiveness and overall performance of Detroit’s entries into the EGR marketplace during the entire 200-mile flip to Kerrville and back. The bottom line is the new-style turbo gives enough quick throttle response to make the time honored technique of getting a run for the next up grade a more effective maneuver. The obvious reason for this performance is the variable speed turbos most OEMs have incorporated into the EGR process.

“Variable speed turbos have been around a long time,” says Phil Rimnac, manager of Detroit’s Series 60 Advanced Product program, “but price was prohibitive. EGR made it necessary to use the power of the variable turbo.” Corralling the correct amounts of exhaust back into the charge air cooler stream of air requires varying the speed of the turbo and creating more flow pressure. This is necessary to shoot inert gases into the pistons from the point where the charge air and the EGR cooler pipe come together to shove cooled exhaust into the air stream.

This pipe requires a word of caution. Its position may tempt some drivers to use it as a handhold while climbing with the hood open. Chuck Blake, application engineer cautions against this. “Despite its name, the pipe is not cool. Using it as a handhold will get you burned.”

Beyond that caution, nothing under the hood gives drivers cause for concern. The cooler and EGR valve are clearly visible on the passenger side of the compartment. But Detroit’s technology for activating the valve and starting the EGR process is hidden from view. One of two air-driven VPODs (variable pressure output devices) gets the signal from the electronic control module to open and close this valve, while the turbo is activated by the second VPOD. The Series 60 variable nozzle turbo, like other turbos put into use to power the EGR process, can spin much faster than the old style turbo. EGR requires more back pressure to push the hot exhaust back through the recirculation system and into the cylinder head. According to Blake, this increased back pressure also makes it possible to boost engine brake performance.

As for maintenance intervals, Blake says, “The no-brainer maintenance level of 15,000 miles remains standard. But Detroit is hoping to raise this basic level to 30,000 before Oct. 1.” Fleets’ preventative maintenance will remain at the now standard level of 25,000-30,000 miles for the time being, according to Blake.

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