If you're running nitrous...
If you're running nitrous oxide, elevation matters even less because you're bringing your own bottled oxygen to the mix. The correction factor for a nitrous'd diesel running high boost would be practically zero.
Myths about diesels that nobody seems to be able to prove have been floating around for some time now, and we decided to find out the truth. We scoured the diesel community for the most controversial topics and then looked even harder for reliable sources who would help us debunk our myths and turn them into facts.
Of course, there are some subjects that'll always be up for debate (for example, Which is better: Chevy, Dodge, or Ford?), but here are some more commonly argued-over diesel myths, along with the most complete answers we could find. We encourage you to guess what the right answer is as you're reading through.
How many gas trucks do you...
How many gas trucks do you see putting out big dyno numbers? Not many. Pat "McRat" McSwain is seen here at Diesel Power Challenge West, where he put out more than 500 rear-wheel horsepower on the dyno. The truck is now up over 700 rear-wheel horsepower without the use of nitrous.
There's been much discussion about correction factors in power levels and whether they should be used in diesel applications the same way as in gas applications. Correction factors are a way of predicting what horsepower an engine will make (or how fast a vehicle will go) depending on the elevation of the dyno run or quarter-mile pass. For instance, the Los Angeles County Raceway has a correction factor of 0.97 for the elapsed time, meaning that if you had a 15-second run at the dragstrip, the corrected time would be 14.55 seconds (15 secondsx0.97 correction factor). All corrected times or power numbers are adjusted to sea-level figures.
So is this right? Nope. Correction factors that apply to gas engines are different from most of those that apply to diesel engines because most diesel engines are turbocharged. Turbocharging brings another aspect (boost) into the equation, which must be factored in. The easiest way to explain this relationship is: total pressure at elevation divided by total pressure at sea level. For instance, there is approximately a 1-psi pressure drop in the air for every 2,000 feet of elevation, so at 4,000 feet, there would only be 12.7 psi of air pressure versus 14.7 psi at sea level. This means that at 4,000 feet, a naturally aspirated engine will make only 12.7 psi/14.7 psi, or 86 percent of its sea-level power.
This is a rough example of a normal correction factor. However, let's say you have a turbo engine running at a peak boost of 20 psi. Now do the math: (12.7 psi+20 psi)/(14.7 psi+20 psi). We see that at 4,000 feet, a turbo engine will be making 94 percent of its sea-level power as long as the turbo can maintain boost pressure at elevation.
So, yes, there are still correction factors for turbocharged diesel engines-just not as high. Another interesting note is that as boost pressure rises, the correction factor is reduced. Say you're running 50 psi of boost instead of 20 psi. The engine would make 97 percent [(12.7 psi+50 psi)/(14.7 psi+50 psi)] of its full sea-level power. As a general rule, a diesel will take about half the correction of a gas vehicle. So at the dragstrip (let's use LACR), instead of using 0.97 as a correction, you would only correct by 0.985 (0.15 instead of 0.3). On the dyno, probably only a few percent correction (5-10 percent) or so is needed, regardless of elevation, because about 7,000 feet is the highest elevation at which you would ever dyno an engine. There are many more factors involved, such as ambient air temps, turbo-efficiency ratings, and so on, but this basic example should help explain why elevation affects turbodiesels-just not as much as you might think.
This is one of those topics that have been argued forever, with both sides yelling till they're blue in the face. So is having a gravity-feed tank legal? Well, the answer is both yes and no.
Smoker tractors are some of...
Smoker tractors are some of the big power-makers of the diesel world. Tractors that are limited by just one turbo can still make 1,500-2,000 hp, while the three- and four-stage monsters are in the 2,500-3,000hp range.
If you're driving a vehicle for off-highway use only (like at a ranch), there's little evidence that the fuel-tank police will suddenly pull up and quarantine your truck. When you operate your vehicle on the highway, however, you have to follow a set of rules.
The actual specification that fuel tanks have to conform to-known as DOT regulation 393.65, or the "all fuel systems" regulation-states that "gravity or siphon feed is prohibited." But it also goes on to say, "A fuel system must not supply fuel by gravity or siphon feed directly to the carburetor or injector." Technically, the law is a gray area because it implies that gravity-feed is illegal if it feeds a carburetor or injector, so if you're running an auxiliary tank that's gravity-fed into a primary tank, it's legal (at least by the letter of the law).
It's only illegal when you have a gravity-feed primary tank that goes directly to the engine. If you're thinking of fabbing your own tank, however, make sure you read the full list of DOT regulations because your tank will have to meet other specs that aren't mentioned here. For a full list of these regulations, go to www.fmcsa.dot.gov.