Driving Cummins' Enhanced ISL
Tom Berg
Equipment Editor
There are many uses for compact, lightweight diesels in heavy trucks — for instance, local or regional delivery tractors that don't need big-bore power, and dumpers or mixers whose owners want to maximize payloads by minimizing tare weight. Medium-duty diesels have been employed in such vehicles, but there are also "heavy duty midrange" engines that combine low weight with durability and long life.
The Enhanced ISL from Cummins is the latest of this type of diesel, and will compete directly with Caterpillar's ACERT C9 and indirectly with International's 570 (formerly the 530) and High Torque 466. The 8.9-liter (544-cubic-inch) ISL has been around for several years, but Cummins temporarily withdrew it from the market as it rearranged its offerings to meet October 2002/January 2004 emissions regulations.
The ISL is now back with a more sophisticated fuel system and a variable-geometry turbocharger, but no exhaust-gas recirculation. Cummins doesn't advertise the ISL's lack of EGR because this would not speak well of the cooled EGR needed on most of its other on-highway models. But without EGR, the ISL is simpler and lower-priced than competitors.
The ISL's enhancements make the engine run cleaner, though it's just over the regulatory line in NOx. But the ISL is still legal because it runs on "credits" granted by the Environmental Protection Agency. Cummins earned the credits by producing large numbers of cleaner-than-necessary ISB diesels, primarily those sold to Dodge for its hugely popular Cummins Turbodiesel-powered heavy pickups.
Does the Enhanced ISL drive any differently than its predecessor, which I drove a couple of years ago? Cummins test engineers who accompanied me on a drive during the recent Mid-America Trucking Show in Louisville thought so; they said the VG turbo provides extra low-RPM boost that makes it more responsive than before.
However, I couldn't feel the VG turbo's boost with the ISL as I could in larger Cummins diesels like the ISM and ISX, or with Detroit's Series 60, where the oomph is quite pronounced and pleasing. It may have been masked by the smooth, quiet character of the test tractor, a Volvo VN. You can't buy an ISL in a Volvo (though you can order the ISX), but Cummins engineers said they use this vehicle because its large underhood area makes installing test engines easy.
The Volvo tractor pulled a flatbed trailer loaded down with big, heavy concrete blocks — a rig brought down from Columbus, Ind., Cummins' hometown; it scaled about 72,000 pounds, engineers said. This may be a few tons heavier than the gross weight range of the typical truck that might use this engine.
The demo ISL was rated at 350 hp and 1,250 lbs-ft., which is the strongest version; the lowest is 310 hp and 1,050 lbs-ft. Thirty years ago Cummins used an 855-cubic-inch NTC to get that much power and torque.
VG turbo whoosh or not, the Enhanced ISL is a hard-pulling machine. On city streets I could start out in 2nd and sometimes 3rd gear and it accelerated respectably. On a nearby interstate, I could shift the Fuller 10-speed transmission into top gear, set the cruise control and keep moving, as bottom-end torque did the job down to 1,300 RPM. But road speed would fall off by as much as 10 mph on moderate interstate-style upgrades.
To keep us at or near cruising speeds, I took my hosts' advice and tried to keep revs above 1,500 in freeway traffic, which gave better response, and downshifted to 9th just before a climb. At 60 to 65 mph, 9th gear in this fast-ratioed tractor kept RPMs at 1,700 to 2,100 and speed seldom dropped more than 5 mph.
Heavy duty features like wet cylinder sleeves and beefed-up reciprocating parts push the projected life of the Enhanced ISL to over 600,000 miles, according to Cummins engineers. And it weighs 500 pounds less than the typical 11-liter diesel found in weight-conscious operations, so if the truck really can go out fully loaded much of the time, the ton-miles and extra revenue can add up.
And the purchase price should be thousands of dollars less than for a bigger diesel, and even for a competitor like the C9 (though Cat people say they've revised their price premiums downward in recent months). Light weight and low price are the main reasons the ISL is being offered by Freightliner, Sterling, Kenworth, Peterbilt and Mack.
To be sure, a bigger engine will provide better performance, which is important in many applications and to almost all drivers. But if smaller and lighter will do, you might consider the Enhanced ISL.
