B_Fuss...torque only tells part of the story, HP tells all of it.
There is no differentiation between HP and torque...they're not unrelated measurements telling different things.
HP is simply how much torque you're making at a certain RPM.
Think about it for a minute, if it was all about torque, then why aren't YOU turning the crank with a huge breaker bar?
I can torque a prop nut on my agcat to 750 ft/lbs which is equivalent to my duramax's output, that doesn't mean I can propel a truck 80mph down the highway hauling a trailer with nothing more than a breaker bar.
If I could crank out 750 ft/lbs on a breaker bar at 5,252RPM, I would be making 750HP (torque and HP measurements are ALWAYS the same at 5,252RPM).
Since I can only turn the breaker bar at maybe 1/2RPM, I'm not making any usable power (like .1HP, which is about right for a human).
That's the difference between HP and torque...torque is a static measurement and HP is how much torque you can produce at RPM.
If the torque curve was perfectly straight, maintaining 100 ft/lbs for example from idle all the way to redline, then the HP curve would be a straight diagonal line from one corner to the other on the graph, intersecting at 5,252RPM.
Torque measurements by themselves won't reflect any kind of useful information other than how all of the engine parts are tuned to each other.
The torque required for a certain task isn't very important, even if it's more than what your engine can produce, that's why we all have a transmission with different gear ratios and sprockets (gearing changes wheel torque output, so you can use the right gear to meet or exceed torque requirements)
Here's a simple thought experiment...a high strung streetbike engine vs. a V-twin torque monster.
The streetbike engine will produce 50 ft/lbs at 10,504RPM, the V-twin will produce 100 ft/lbs at 5,252RPM (twice the torque, half the RPM).
Both bikes are running the same exact speed in a drag race....the streetbike is in a lower gear because it's running at twice the RPM (let's say it a 2:1 drive ratio at the wheel) and the V-twin is in high gear (1:1).
Which one has more wheel torque?
A: They're both the exact same.
If they both have the exact same torque output, they should have the power to accelerate equally, correct?
Well, let's look at it a little closer.
The V-twin is making 100HP, the streetbike is making 135.6HP (using a torque to HP calculator)
All other things being equal in a perfect world (say both engines were swapped out on a testbed vehicle), the streetbike would win in a race due to having more HP, even though the engine itself is not making as much torque.
So when you see a graph with only HP measurements, just know that it's telling you USEFUL information.
If you want to get an idea of what the torque is on a HP only graph, just fill in this calculator to get the number:
http://ncalculators.com/electrical/horsepower-to-torque-calculator.htm
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