Everybody know diesels can kick the pants off a gas engine in torque, but what about horsepower? After all, if you have 1,000 lb-ft of torque and the guy next to you has a gas engine with 1,000 lb-ft of torque, you're still going to lose. That's because he probably has 1,000 hp to your 500 hp.
So can diesel engines really be as powerful as their gas counterparts while still having a torque advantage? For this answer, we have to go to the most powerful engines in the gas and diesel worlds-leading us to the light-and-fast world of drag racing and the heavy-and-slow world of tractor pulling. In drag racing, the Pro Modified class is one of the best examples of what a no-limits gas engine can do. With cubic inches in the 700-plus range, racers using naturally aspirated engines and 1,200 hp worth of nitrous oxide are pushing numbers in the 2,500hp range.
Mike Moran, who runs a turbocharged entry in the class, is thought to be in the 3,000hp range. By contrast, Super Stock-class diesel tractors can have up to 640 ci of displacement (that's 11 liters), run up to four turbos, and reach 250 psi of boost in the sled-pulling world. All this pressure adds up to horsepower in the 2,500-3,000hp range, as far as anyone can guess. The engines are roughly the same displacement, and oddly enough, have about the same airflow capability, but each uses its own strengths to the fullest. The gas engines will spin nearly 8,000 rpm despite their size, while diesels use half the rpm and five times more boost to generate similar power numbers. So can diesel compete with gas for all-out power? You bet.
Many gas engines that make big power also use turbocharging. Typical boost pressures on racing engines will run in the 30-40-psi range. | 
Power versus emissions: If you decide to go crazy and have a hot program to make big power, your emissions might be, uhh, slightly affected. |
This is an underside view of the particulate filter on an '07 Dodge, which is promised to be one of the cleanest of the new diesels. | |
Meeting emissions regulations isn't getting easier. In fact, the regulations are becoming a lot more stringent, and some people are worried that diesels won't be able to make the cut. Will they? It might shock you to learn that not only are diesels clean, but some (like the '08 Ford F-series) are also considered ultra-low-emissions vehicles.
Get used to seeing emissions-control regulations on diesels. Stickers, EGR, and various exhaust filters are all being used to control emissions on new diesels.
Achieving this was by no means easy, and it required EGR, particulate traps, and a few other tricks to reach the desired goals. Common-rail technology has also allowed a more precise fuel burn, making it much easier to meet the new emissions standards and gear up for 2010 (when emissions will practically be dropping to zero).
The '08 Ford we've driven for a while goes into regeneration mode after long freeway drives, where it idles at approximately 1,100 rpm (up from its normal 500 rpm). This is to burn out all the soot that collects in the particulate trap and also results in the new Chevys and Fords having some funky-looking exhaust tips. Can diesels be clean? Yes, but it isn't easy. A lot of work and engineering went into the new emissions-friendly diesels, so remember that when you're looking at the price of the '07 models.