Who makes the world's best diesels, GM or Mercedes?

[Muscle Master]

Originally Posted by Motor Trend

t's almost an epidemic. In the last two weeks, we've listened to three big automakers make thoughtful and detailed presentations about their current and future engine lineups. Clearly, they want us to know they're working their butts off to get the best technologies (meaning the most fuel efficient ones) into your next new vehicle. They want all of us to know they've got a coordinated powertrain strategy and their choices aren't random. Companies like Mercedes-Benz and General Motors seem to have the lead when it comes to state of the art diesel technologies, and recently we've had a chance to look at both with a magnifying glass. Here's what we've seen.


Mercedes-Benz BluTEC diesel engine

Mercedes-Benz BlueTEC

The newest generation of BlueTEC, now currently in three of the M-B's newest models (the R-Class, ML, and GL), uses an aluminum 3.2-liter V-6 engine with a variable vein turbocharger, sophisticated common rail injection mapping, and one of the most aggressive after treatment (basically in the exhaust system) strategies anywhere.

The key to the system, we're told by M-B, is finally having the proper ultra low-sulphur fuel in order to start the whole process as clean and strong as possible. After that, the first priority is making the burn in the engine as clean and strong as possible.

Next, a four-stage emissions cleaning system starts with the oxidization catalysts to scrub out carbon monoxide and unburnt hydrocarbons. After that, the particulate filter collects 99-percent of the soot from the exhaust gas, then burns it off when necessary during a computer-controlled regeneration process (not unlike a self-cleaning oven works). Finally, an inert liquid (M-B calls it AdBlue but its essentially urea solution) into the exhaust, converting the remaining NOx molecules into harmless nitrogen and water in the final selective catalyst reduction (SCR) process. The result is the cleanest exhaust fumes you'll ever see or smell. In fact, we got down on our knees and took a big whiff with our nose stuck into the exhaust and couldn't smell or see anything. This system allows M-B to be the first diesel manufacturer (if you don't count Cummins-they did it last year in their work-duty B-motors) to meet be 50-state compliant before the 2010 emissions regulations deadline.

In fact, they say it will also allow them to meet the next gen European EU6 requirements coming in 2015. We recently drove the R 320, ML 320, and GL 320 BlueTEC offerings over several one-hour and two-hour loops through the Vermont countryside and averaged 29.0 mpg in the R-Class, 28.4 mpg in the ML, and 27.6 mpg in the GL; just what you might expect given their various weight differences. With 398 lb-ft for torque (210 hp), the engine is comfortable staying at 1800 rpms no matter the hilly conditions we hit, but it is worth noting there weren't many opportunities to get above 60 mph. And it certainly doesn't hurt that M-B has a wonderful 7-speed trans (complete with paddle shifters) ready to smoothly respond to any driver situation.

The Newst Duramax

Right behind the M-B technology is the all-new Baby Duramax 4.5-liter V-8. We've been hearing about this for a long time but GM is now ready to put into their 2010 model light-duty pickups-the Chevy Silverado and GMC Sierra-and you can expect it get into the fullsize SUVs pretty quick after that. The new Duramax is unique in many ways, challenging several traditional diesel engine building assumptions. GM, like many others, is projecting huge growth for diesel in general and specifically for U.S. buyers. The new diesel is a compact, relatively light-weight, high-tech engine that actually gets more power and torque than did the larger big-brother Duramax 6.6-liter V-8 when it debuted in 2001.
GM Duramax 4.5-liter diesel engine

After the preliminary test, GM is conservatively predicting the 4.5L V-8 to get 310 horsepower and 520 lb-ft of torque. From the beginning, using a clean sheet of paper, Charlie Freese, Executive Director Diesel Powertrain, questioned every piece of conventional wisdom to diesel building. Among some of the most impressive changes his team's computer modeling came up with was a composite graphite block banked at 72-degrees, a variable-vein turbo mounted directly to the cylinder head (accomplished by sticking it in the block valley), he integrated the exhaust manifold into the aluminum four-valve cylinder head, basically reversing the air-flow (with intake air coming in where a set of exhaust headers would normally sit, then exiting in the valley to spin the valley-planted turbo) through the engine in order to create a lighter, less complicated (with 70 parts), more powerful diesel engine. And, with the help of existing oxidation scrubbers, particulate filters, and their own brand of urea injection, they fully expect this vehicle to meet all the hurdles the 2010 (Tier 2, Bin 5) targets will require, which means it will be 50-state legal as well. GM isn't stating any fuel economy numbers but they are saying it should be at least 25-percent better than a comparably sized gasoline engine, which puts it in the range of 18 or 19 mpg in the city, and 26 and 28 mpg on the highway, depending on the transmission. And doing it all with a 13-percent improvement in CO2 emissions and a 90-percent improvement in NOx and particulates when compared to current diesels. Of course this engine won't be for everyone, but we predict the appeal will grow.

Who Wins?

If these two engines and emissions technologies are any indication, both companies seem to be allocating their skilled powertrain resources in the right direction, with amazing results. And we expect to see more. But if these engines were two boxers, we'd have call this a technical knockout in favor of M-B because the BlueTEC engines are being dropped in vehicles right now and we're still about a year away from driving GM's new Duramax. Still, both systems are impressive and a clear signal that choices are going to get a lot more complicated real fast. But if that means driving more diesels in the trucks we love, it makes more sense than ever before.
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I agree with this article MB seemed to have the best diesel engine right now, I mean who puts there nose in a exhaust pipe and smell nothing but clean air.......amazing