With new emissions rules looming in October, there are still plenty of questions about the performance of diesel engines that must meet the standard. What’s certain is that most will use cooled exhaust gas recirculation (EGR) or other equipment to cut stack emissions to the U.S. government’s satisfaction. The new engines will cost more to buy and operate, but we don’t yet know how much.

Some good news is that in most cases, from the flywheel rearward, your existing powertrain spec need not change. There are no new torque forces coming from the October engines, so you won’t need a tougher clutch, transmission, driveline, or axles.

Starting Oct. 1, engines must be certified to the U.S. Environmental Protection Agency’s NOx+NMHC target of 2.5-grams per brake horsepower-hour. NMHC+NOx is non-methane hydrocarbons and nitrogen oxide, a contributor to greenhouse gas. The current standard is 4 g/bhp-hr. Manufacturers must pay a fine for each engine that fails to meet the 2.5 g/bhp-hr limit (related story, page 16).

This alone will limit the availability of big diesels, at least for now. Caterpillar and Cummins will suspend sales of their 600-horsepower, 2,050-pounds-feet models. Caterpillar’s strongest engine will be a 525-hp C15 (higher ratings will accompany the release of new technology next year). Cummins will delay its Signature 600, offering a 565-hp ISX instead. The C15 and ISX each will make no more than 1,850 pounds-feet of torque, and most ratings will have 1,750 pounds-feet or less.

At Cummins, there will be common engine architecture across the entire ISB/ISM/ISX line, including a new electronic control module and variable-geometry turbocharger. The external package won’t look much different, except for the EGR cooler, a standard tube-type heat exchanger made of stainless steel. Cummins says the ISM and ISX engines will be 110 and 130 pounds heavier, respectively.

Likewise, Detroit Diesel will drop its 14-litre Series 60 500-, 550-, and 575-hp engines until spring, when a 500 will reappear with 1,650 pounds-feet of torque. Detroit engineers tend to classify things according to torque rather than horsepower, and are figuring out which displacement to use for 1,550-pound-feet models. It might be a 14-litre or a 12.7-litre, or both. The engines will use a variable-geometry turbo, slightly different injectors, and the same DDEC IV controls as we have now. The 12.7-litre engines will actually be 25 pounds lighter than present products, and the 14-litre version will stay the same.

Come October, Mack will drop the torque output from 1,450 pounds-feet to 1,250 pounds feet on its 12-litre Maxidyne diesels, and offer new 335- and 370-hp ratings. Also, the current operating range of 1,000 to 1,750 rpm will jump to 1,700 to 2,100 rpm. Maxidynes will use internal EGR, a simple system that works well in vocational trucks. Econodyne and MaxiCruise versions of the 12-litre diesel will go primarily in highway trucks, so they will get cooled EGR, which is more complex but also more fuel-efficient at highway speeds.

Mack’s E7 engines will use a variable-geometry turbo, along with a higher-capacity water pump, and modified V-MAC electronics. Available horsepower range will cover 300 to 460.

Volvo’s 12-litre V-Pulse diesels will not change in torque output or operating ranges, so driveline components should not be affected. The new engines will use the same turbocharger as at present, except for engines with 430 hp or more, which will use a wastegated turbo. The only change to the cooling package is a new 11-blade fan. Oil capacity stays the same, as does weight.

Caterpillar’s product strategy has two phases, neither of which involves EGR. Next year, the company will introduce engines equipped with its Advanced Combustion Emissions Reduction Technology, or ACERT.

To date, Cat has provided few details about how ACERT works. The first ACERT engine-a new 9-litre C9-will not be ready until January, and big-bore ACERT models won’t be produced until next spring; Cat planned to use a second aftertreatment device-a particulate trap-for the bigger ACERT engines, but recently said it will instead use double turbocharging and double aftercooling.

To bridge the gap between October and ACERT, Cat will sell engines that use a catalytic converter in conjunction with a muffler to soak up NOx. It’s the same relatively simple technology that’s been used on the mid-range 3126 for quite a while. Of the 100,000 such converters in the field, there have been but three failures.

The engines, marketed under the Clean Power name, will miss the EPA’s 2.5 g/bhp-hr target, so Cat will be fined for each engine it sells. The company considers it short-term pain for long-term gain, claiming that ACERT will be worth the penalties it will have to pay for Clean Power engines. The company says ACERT will be a more reliable, more effective alternative to EGR, and is the foundation of its efforts to meet even tougher emissions standards in 2007.

Torque capacity of your drivetrain components mated to post-Oct. 1 engines need be no more than now, or perhaps less than what you’re used to spec’ing. You should upgrade driveline components if you plan to uprate your engine later. There will be some changes among each builder’s engine “families” in what can and cannot be uprated; check this out before you order.

The most significant spec’ing consideration comes from Mack, where the Maxidyne’s new rev range is not only higher, but shorter by 250 rpm. So Mack has added one more transmission gear: a pair of new 6- and 7-speed gearboxes will be mated to the Maxidynes instead of the current 5- and 6-speed offerings. Like the current transmissions, the new TM308 and TM309 boxes have two additional low-low ratios handy for off-road manoeuvring or starting out on steep grades.

With one extra ratio to run through, the new, less “torquey” 300-hp Maxidyne performs every bit as well as the current stronger model, Mack engineers insist, noting that test drivers say it feels gutsier. Cruising revs also climb in the new Maxidynes, from 1,500 to 1,700. Meanwhile, the overdrive-high gear on the new transmissions stays about the same. So the truck needs a faster (numerically lower) axle ratio. It’s important that the truck be set up right and driven correctly, or the Maxidynes will not deliver the performance or fuel economy they’re meant to.

The high heat rejected from EGR systems is demanding on cooling systems, though recent testing shows it’s not the big problem that truck builders once feared. Some of the heftier EGR-equipped diesels will need bigger cooling packages, but engines with more modest torque and horsepower won’t need them.

For example, Detroit Diesel models that produce 1,550 pounds-feet of torque will need a radiator with 1,350 square inches instead of the current 1,200-square-inch unit. But models making 1,450 pounds-feet or less can stay with the smaller radiator. The bigger radiator will weigh a bit more, enough to cancel out the 25-pound weight reduction Detroit Diesel has achieved for its 12.7-litre Series 60.

Mack is installing an “inverted” radiator-charge-air cooler package, with the cooler behind the radiator instead of in front of it, on some Vision tractors. Tests show it just works better that way, but not on all truck models. On other models Mack is using a fan “ring” very close to the tips of the fan blades. This funnels air more efficiently than a wider-diameter shroud.

You can still avoid EGR if you’re willing to try an imported diesel. Because the EPA’s consent decree affected almost no foreign-built diesels, they will not need to meet the 2.5 g/bhp-hr limit until January 2004. So you could spec a medium- or heavy-duty Mercedes-Benz diesel in a Freightliner, Sterling, or Western Star.

In medium-duty trucks, no Japanese import will need EGR. Mack’s Freedom will. Most domestic trucks with Cat and Cummins diesels will have EGR. International will use EGR on only one of its diesels. General Motors’ Duramax diesels don’t need EGR until 2004.

So, take your spec’ing notebook and go figure. Most of your pondering will be under the hood. Don’t let it fall on you.