Post in the 'Autos' forum and I might help.

Torque is dependent on RPM and work generated by the equation:

In SI units -  Work out [kW] = (T * n)/9549 where T = torque [Nm] and n = rotations/min [RPM]

In English units - Work out [hp] = (T * n)/5252 where T = torque [ft-lb] and n = rotations/min [RPM]

Hope that's what you were looking for.

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Torque can be independant of RPM. Let's say a 200 lb person puts a one foot long wrench on a bolt and applies all their weight but the bolt doesn't move. There was still 200 lb-ft of torque applied but with no RPM (rotation). Torque(lb-ft) = Force(lb) x Distance(ft), or 200 lb x 1 ft = 200lb-ft.
One other thing that has to be accounted for is gear ratio. A 3:54 ratio will apply more torque (do more work) at the wheels than a 1:1 ratio, but the 3:54 ratio would be less efficient at speed. 
In the internal combustion engine peak torque will always occur at a lower RPM than peak horsepower. This is because torque is dependent on cylinder efficiency; Less air/fuel = less torque. And since HP = Torque x RPM the rate that horsepower will fall off depends on how fast the torque curve drops off.
What a designer has to do is study the horsepower and torque curve. The peak effeciency will fall somewhere between these two curves. In the big picture parasitic loads also have to be taken into consideration. Confused yet?

Now you have me interested...   What's the advantage of using Diesel?
More air/fuel = more torque?
I'm assuming that means that Diesel engines have more cc cylinder volume?

Makes sense. All the big 4x4s use Diesel and have large cylinder capacity.
How come diesel engines support this better than other fuels?

Because it is an RPM limiting factor?    
Okay, off to lectures (Applied engineering
in French, yey...  ).

Alphajet_Enthusiast wrote on Oct 16^th, 2007 at 5:05am:

Not necessarily. GM built a 350c.i. diesel in the late 1970's patterned directly from the 350c.i. gasoline engine. It also produced more torque and was more effiecint (30mpg in the Oldsmobile 98) simply from the higher compression ratio and the longer burn rate of diesel fuel. It's downfall was GM's failure to strengthen the cylinder heads. Many owners simply converted them back to gasoline engines. A V-6 was later made from the same casting, minus two cylinders, and it worked well.

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Some car company, possibly Renault?, is currently testing a high-revving turbo-diesel with great success. It has great economy and power. I believe it is around 2 Litres in size.