Understanding What Makes Torque

[bryanearll]

I've been wondering what makes one engine have more torque than another. I understand that the computer chip programming on two identicle engines might make a difference, but more significantly what makes a 'truck' engine vs. a 'car' engine?

Or why does an old school 'in-line' straight 8 have more torque than a V8? (assuming it really does)

Is more torque developed on a shorter stroke with a larger diameter bore rather than a longer stroke with smaller bore but equal displacement? Which engine in this example would you want to run 'all day' on?

Is there a diminishing return on number of cylinders vs increasing bore diameter on a fewer number of cylinders to achieve the same displacement? What would be the benefit of each?

What advantage is the Boxer Engine's opposing cylinders vs. a V shape etc.?

How do Vario Cam's mechanically adjust timing when responding to the computer's input?

I'm sure all of this is really fundamental to understanding engine design, so maybe my real question is: can you point me to a good technical link on understanding engine design please?
Bryan

[ttweed]

... can you point me to a good technical link on understanding engine design please?

Torque vs. HP, etc:
http://science.howstuffworks.com/fpte.htm
http://science.howstuffworks.com/engine.htm
Variocam:
http://www.panix.com/~clay/cayenne/variocam.html
Boxer configuration was chosen for balance (opposing forces on crankshaft cancel each other out) and packaging issues (lower CG)
http://encyclopedia.thefreedictionary.com/Boxer+engine

[bryanearll]

Thanks very much Tom for the detailed links.
Bryan

[bryanearll]

So talking to a neighbor mechanic this afternoon (Ford man FTW); he builds and tunes track cars for the local boys....

Anyway, he says that horsepower is bunk, nice to have a bunch of it... but when push comes to shove it's Stroke length not HP that will determine how much 'power' you have when you hit the gas...

Any comments?
Bryan

(Question was 'to him'; what give a car 'off the line' torque.)
Big block Ford has a 4" stroke... (smile, he says) Indy Cars may have equiv. horsepower but it takes 'em laps to get there and no power out of the pits....

[ajackson]

Those links are very good, you should go through them. Horsepower is the final measurement of how much you can accelerate. Maybe the confusion is that even though a car has a max hp, it doesn't make that much all the time. You may have a 1000hp car, but it may only make 50hp at 2k rpm. If you stomp on the gas at 2k rpm, you aren't going to move very much. A torque curve will tell exactly what power an engine makes and where. Hp is just torque times the rpm times a constant.

[kary]

Those links are very good, you should go through them. Horsepower is the final measurement of how much you can accelerate. Maybe the confusion is that even though a car has a max hp, it doesn't make that much all the time. You may have a 1000hp car, but it may only make 50hp at 2k rpm. If you stomp on the gas at 2k rpm, you aren't going to move very much. A torque curve will tell exactly what power an engine makes and where. Hp is just torque times the rpm times a constant.

That is why gearing is so important in a race car! It needs to keep the engine at its peak power.

[76914]

Those links are very good, you should go through them. Horsepower is the final measurement of how much you can accelerate. Maybe the confusion is that even though a car has a max hp, it doesn't make that much all the time. You may have a 1000hp car, but it may only make 50hp at 2k rpm. If you stomp on the gas at 2k rpm, you aren't going to move very much. A torque curve will tell exactly what power an engine makes and where. Hp is just torque times the rpm times a constant.

actually to be a jerk about it hp is fake. there is not such thing. it was invented by a steam engine designeer to help sell his new engine, he invented a calculation that allowed him to claim it could produce all the power a horse could. hp is defined as 1hp= 33000-lb.ft/ 1 minute. Hp is than in every sense a form of torque, and can therefore be expressed in relationship to torque as hp=(torque X RPM)/ 5252. if you guys want i have some more formulas that u cna use to determine other fun thing such a Mean Effective Piston Speed, and a pretty accurate guide to what you will run in the 1/4 mile

[ajackson]

Hp being fake is a misnomer. Hp is very real, in physics, it the concept is called "work". It is force applied over a distance (or in this case rotations). My last sentence did mention the relationship between hp and torque. Making up a new unit and giving it a definition is done all the time to express things in ways that make sense to someone.

Hp is the final measure of what your engine is doing.

[76914]

Hp being fake is a misnomer. Hp is very real, in physics, it the concept is called "work". It is force applied over a distance (or in this case rotations). My last sentence did mention the relationship between hp and torque. Making up a new unit and giving it a definition is done all the time to express things in ways that make sense to someone.

Hp is the final measure of what your engine is doing.

work is already defined as torque in your engine, horsepower is literally the mathematical translation of how much work that engine can do literally compared to a horse.

[ajackson]

Horsepower is a unit of work.
ft-lbs is a unit of torque (which is angular force).

They are two separate and distinct concepts. I'd recommend looking up a physics tutorial (or book) on the relationship between work and force.