Torque and power quiz 4

[yoshimitsuspeed]

I spend a lot of time in the automotive community and a lot of time on car forums and groups.
Ever since I started to learn the actual relationship of torque and power it drove me crazy how few others in the automotive world actually understood this basic formula. People capable of building motors that make 500 hp per liter and who still think that torque is low end power.
I have gotten into enough arguments with people to learn that most would rather argue relentlessly cause that's what theys daddy taught them than sit down and think about the simplicity of the formula long enough to understand the relationship of the two.
I have decided to try a different tact and make a little quiz that gets people thinking about this from a different angle and maybe hoping they will get the point that torque and power can't be compared, and that torque does not mean low end power.
I just started on this tonight and it's 3AM. I want to do more to improve it but I also would love some input from others on ways I could improve it.
I would like it to be as detailed and informative as possible while still being interesting and keeping the person engaged and interested.

Tell me what you think of what I have so far.
What could I do better?
What are other questions I could ask or ways I could put things to get people thinking about the relationship without getting too bogged down in the math to loose too many people?
On that note should I focus more on the math or stay more with the basic relationship and principles?

http://matrixgarage.com/content/think-you-understand-torque-and-power

 

[140Airpower]

"Quote: Heck, a meaningful HP curve can even be created without knowing engine rpm.
I'm afraid I'm not grasping what you'd be plotting HP against if not rpm.
Norm "

Power can be plotted against vehicle speed, not knowing engine rpm or even if there is a rocket engine or any engine involved at all. It can be plotted against time or accumulated energy (1/2mv^2), etc.
This is especially relevant when we plot hp vs vehicle speed under acceleration.

I think engineers look at quantities as "fundamental" if they are easiest to measure. On a brake dyno you just look at the reading on the scale and multiply by the radius of the beam. But the scale measures force, not torque and it is represented as potential energy (compression of a spring or lifting of a balance weight, etc). Therefore force is a derived quantity.

 

[140Airpower]

Just to elaborate on the brake dyno, the irony is that to load the engine you use a friction brake or water brake, etc because, unlike a static torque measurement you have to have the engine running. The process produces a lot of heat and this heat is proportional to the engine's speed and the retarding force which shows up as weight on the scale. This is exactly POWER. It takes power to measure torque on a dyno. So torque is derived from power. But, it is not convenient to measure the delta T and precise flow rate of the cooling water so engineers get the power figure by calculating backward from the measured torque.

The vehicular power figure for a car without an engine or engine not running would be for the brakes retarding a downhill coast or, like in "Furious 7", a car dropped from a plane converting only some of the potential energy into kinetic -which would be a perfectly efficient process except for air drag. The power figure would start at zero and build up to the point of terminal velocity and level out, slowly increasing with decent into thicker air.

 

[LionelHutz]

You could plot power vs % if you wanted. Assume the initial dyno rpm is the starting percent and the peak dyno rpm is 100% speed. Fairly simple to do and it would roughly gives you the power vs rpm once you equate 100% with the peak rpm of the engine.

 

[Tmoose]

http://smartpei.typepad.com/.a/6a00d83451db7969e201b7c713d957970b-800wi

http://bloodgarden.com/p7hg_img_1/fullsize/4-horse_bogged_in_mud_fs.jpg

Nary a lb-foot or rpm in sight.

 

[LionelHutz]

Nice links

I really need to type better. If you plot HP vs % dyno rpm by using the peak dyno rpm as 100% then you get a HP curve which you can roughly match to the engine operating range. You can't do that with torque and get a meaningful curve.