I posted this to rec.autos.driving and didn't get great response, so
was hoping you more technical-minded individuals could help me with
this. :) Much appreciated.

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First off, sorry to ask about this topic again (it must have been asked over and over since cars were invented). But I've searched the web and the group archives and couldn't get a satisfactory answer. I'm hoping some kind soul can answer my question and explain the reasoning, keeping in mind I may ask other questions as well. :) I would also love if you could EMAIL me your respond, since it's much easier than fishing for replies on google.

So, without further ado, the question (as clearly and concisely as I can ask it):

My car is at a standstill. I rev and hold at #### rpms. I quickly release the clutch and assume ideal, total transfer to the car's motion (no clutch slip, so tire squeal, etc) Which rpm would give me maximum acceleration, max torque or max horsepower (or some other)? And, more importantly, why?

My vague understanding: Torque and horsepower are both related to the car's acceleration, since

a) torque is proportional to force, which is mass x acceleration, or "increasing the velocity of a mass at a certain rate".

b) horsepower (or power) is the rate of change in kinetic energy, which is proportional to velocity squared. So if I'm increasing my "velocity squared" quickly, I must be accelerating quickly...?

Please email me your response, and put one more soul to rest about this confusing topic.

Thanks, Nick

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I've thought about this some more, and have some more specific questions:

1) If an engine delivers say 200 lb-ft of torque at 5000, is that regardless of how open the throttle is? If I'm in neutral and rev to 5000, is it still putting out 200 lb-ft of torque?

2) When I partially apply the clutch, is the engine delivering all it's force to its load (the car)? I'm inclined to believe that if I hold the engine at a certain rpm, apply the clutch JUST to the point before the rpms drop (but no less), I am applying EXACTLY the torque for that rpm to the load. If I release the clutch any more, I'm overloading the engine at that rpm; any less, and I'm not applying the full torque at that rpm.

3) How, numerically and assuming ideals, does the value of engine torque ("200 lb-ft @ 5000rpm") translate to the car's acceleration ("6 miles/hour/sec")? Is there a formula for this? Is it as simple as: Acceleration = torque * drive radius / car weight ? (where drive radius is the factor based on the radius of gears and wheel, essentially converting torque to linear force) This doesn't seem right because it doesn't consider rpm.

Please respond via email. Thank you.

Nick

----------------------------------------------------------------------

First off, sorry to ask about this topic again (it must have been asked over and over since cars were invented). But I've searched the web and the group archives and couldn't get a satisfactory answer. I'm hoping some kind soul can answer my question and explain the reasoning, keeping in mind I may ask other questions as well. :) I would also love if you could EMAIL me your respond, since it's much easier than fishing for replies on google.

So, without further ado, the question (as clearly and concisely as I can ask it):

My car is at a standstill. I rev and hold at #### rpms. I quickly release the clutch and assume ideal, total transfer to the car's motion (no clutch slip, so tire squeal, etc) Which rpm would give me maximum acceleration, max torque or max horsepower (or some other)? And, more importantly, why?

My vague understanding: Torque and horsepower are both related to the car's acceleration, since

a) torque is proportional to force, which is mass x acceleration, or "increasing the velocity of a mass at a certain rate".

b) horsepower (or power) is the rate of change in kinetic energy, which is proportional to velocity squared. So if I'm increasing my "velocity squared" quickly, I must be accelerating quickly...?

Please email me your response, and put one more soul to rest about this confusing topic.

Thanks, Nick

---------------------------------------------------------------------

I've thought about this some more, and have some more specific questions:

1) If an engine delivers say 200 lb-ft of torque at 5000, is that regardless of how open the throttle is? If I'm in neutral and rev to 5000, is it still putting out 200 lb-ft of torque?

2) When I partially apply the clutch, is the engine delivering all it's force to its load (the car)? I'm inclined to believe that if I hold the engine at a certain rpm, apply the clutch JUST to the point before the rpms drop (but no less), I am applying EXACTLY the torque for that rpm to the load. If I release the clutch any more, I'm overloading the engine at that rpm; any less, and I'm not applying the full torque at that rpm.

3) How, numerically and assuming ideals, does the value of engine torque ("200 lb-ft @ 5000rpm") translate to the car's acceleration ("6 miles/hour/sec")? Is there a formula for this? Is it as simple as: Acceleration = torque * drive radius / car weight ? (where drive radius is the factor based on the radius of gears and wheel, essentially converting torque to linear force) This doesn't seem right because it doesn't consider rpm.

Please respond via email. Thank you.

Nick