Well, that's just dumb....if it wasn't for that, we wouldn't go anywhere..

 

wasnt for what? the movement of the piston?the whole is not the sum of its parts in this case. so just knowing the speed of the piston is as easy as knowing your stroke and the rpm. again, this isnt really useful. as far as output is concerned a motor makes only torque and isnt translated into horsepower until it hits the wheels

 

Pepsi and Coke are NOT the same:P

 

to be honest..this wasnt supposed to be adebate about what HP and torque is, just wonderin what you guys like more[8D]

 

see tho, u cant pick one over the other. thats the point were making. you can only pick WHERE you like your torque. do you like it down low, or up high?

 

i see what you are saying and you make a great point..but you guys know what i meant. lowend torque or highend torque?

 

In the simplest terms....

Torque = Twisting force,,,,, "Right now" Time is not a factor

HP = Twisting forcewith "y" amount of time factored in...

1 HP = the work required to lift 33,000 lbs 1 foot in one minute.

For a torque reading only the actual twisting force produced by an engine need be known..... (Likeweight restingon a scale)

For a horsepower reading, the actual twisting force (work) and the speed at which this workis being donemust be known values. (twistat any givenspecificRPM, plotted with mathematic formula applied)

Horsepower is a "more complete" measurement of power producedthan torque, but while HP and torqueare inseparablytied together, eachreading delivers it's own important information regarding engine performance and potential.

Horsepower and torque are kind of like Al and Peg Bundy, "they go together like a horse and carriage"....

The average person can deliver several hundred pounds of torque with a long torque wrench. This "torque reading"carries the same value and accuracyas the torque reading that a dyno will deliver.

While it is easily possible for a human to exert more torque than virtually anyengine,in anyMustang represented on this entire forum,a humancan not deliver enoughspeed with this leverage to convert this massive torque into even a fraction of a single horsepower....

So while a human can produce massive amounts of torque, a human will never produce more than about 1/4 HP.....

Torque can be measured with (virtually) no motion at all,but no motion = no work. In this particular case the torque readingis meaningless.

For a horsepower measurement, there must be motion, and therefore there must be work being done.

Motion + Torque = HP
No Motion+ 1,000,000 ft lbs of torque= 0 HP.
10,000 RPM+ 0 torque = 0 HP

 

Well, let's try to explain this for those who want to understand what's actually going on in an engine. It's a lot of info, but try to follow along from beginning to end. I'll try to make it as simple as possible using some of the basic stuff we learned in high school(or in the case of some here, are/will learn). I'll also include a brief explanation of why we shift past where the engine pulls for best performance at the end.

First, keep in mind what was mentioned above about work and force. That torque is a measurement of a force(lbs) around an object of a given radius(foot). In the standard measurement in the US we use lb-ft which is 1 lb of force exerted in a rotational manner around a center at a 1 ft radius. If it helps, imagine a crankshaft in an engine with a massive 2ft stroke, such that the length from the center of the crank to the center of any crankpin is 1 foot. Power is the measurement of how much work(lb-ft) that can be done in a given amount of time(usually minutes). This is very important for understanding how power is MEASURED in an engine(we talk often about power produced, but as was stated above, power is a derived number, work is produced and power is calculated).

Now for any engine we all already know this measuring standard as RPM(rotations per minute). To simplify this think of it as DISTANCE/TIME, and here is why(some of you prolly already see where I'm going with this). In an engine when we calculate power output and measure the torque output, it's always at an RPM. The M is constant, at 1 minute(our time element in determining horsepower, remember that hp = force * distance / time). What does change is the number of rotations in that given minute. Rotations is the DISTANCE, this is because the force that is generated during combustion is translated through the connecting rod to the crankshaft that is made to rotate by that force. Our crankshaft is basically a big lever with the force being exerted where the conecting rod attaches(our 1ft radius for purposes of measuring torque). This causes that point of force contact(the crankpin) to rotate in a circle, 1 full revolution being a complete circle, that has moved a distance of PI * DIAMETER(D of the circle, which is also the stroke length of an engine). That means that in RPM, the R is distance traveled, which is PI*D*NUMBER OF ROTATIONS, and M is always one minute. Rotations(distance) per minute. So we are left with the distance traveled(determined by the stroke of the engine) in 1 minute. You can see here how increasing stroke length effects the output of the engine(a larger distance traveled in the same number of revolutions).

Now comes force. Combustion's goal is to generate PRESSURE. Preasure is measured as POUNDS per SQ INCH, pr PSI. Now, our piston has a given surface area that is in contact with combustion, with a surface area of (some number) of SQ INCHES. Using PSI of combustion pressure, we can multiply to find the actual force in LBS that combustion is generating(punds per square inch * SQ IN). You can see here where the bigger bore increases output of the engine as well(provided pressure stays the same). This is one of the factors in why larger engines produce more power.

Now this force generated in LBS is exerted through the connecting rod to the crankpin, where the force is applied across a given DISTANCE(through the distance the crankpin rotates in 1 full revolution). And it all does so in the constant 1 minute period(or that is to say we always convert our measurements into a 1 minute constant). Remember we always measure by 1 minute, changing the distance traveled in the same 1 minute period by turning more revolutions. We end up with FORCE(pounds from combustion exerted on the piston surface area) * DISTANCE(the distance traveled at the circumference of the crank which is the center of the crankpin in this case) / TIME(the 1 minute constant that we use). FORCE*DISTANCE/TIME=HORSEPOWER.

Now, that's the VERY basics of how the HP equation works in an engine. In reality there are more complexities as you have to deal with losses due to friction, and losses due to the angle of the rod relative to the position of the crankshaft and piston(leverage gains and losses) etc. It should also be noted that the combustion pressure is determined by many things, but primarily we focus on the rpm aspect and WHERE in the rpm range pressure is highest. The highest combustion pressures generally coincide with peak torque output, which is determined primarily by the build of the engine. Horsepower is CALCULATED(or derived), and is higher when either combustion pressure or rpm is higher with enough combustion pressure. Higher horsepower engines either are such because combustion pressures are VERY high and rpm remains lower(think deisel engine) or because rpm is higher and combustion pressures stay somewhat low(think Formula 1 engine).

For our case, automotive use, horsepower is important to know if you know the rpm it's at and how to set the car up. Gearing in any vehicle(the transmission and differential) has the job of taking whatever torque is being produced at a given rpm(calculated HP) and multiplying it by those ratios, so that the ultimate torque output at the wheels is greater than at the engine. Now when we have a high rpm/hp engine, the torque output may be the same as a lower rpm engine, but the torque occurs at a much higher rpm. This would normally lead to an engine that is very sluggish at first as the vehicle struggles to work through the much lower efficiency at low rpm until it can get to the higher torque output rpms, so we solve that problem with gearing(which also gives us other advantages). Since the higher rpm gives the engine a wider range to operate in, we can put a lower gear in the trans or diff to multiply the power even more and not have to worry about rapidly topping any given trans gear out too quickly or having reduced top speed. This helps out the lower rpm power loss by taking the reduced amount of torque at low rpm and multiplying it, but more importantly for performance, takes the torque at much higher rpm and multiplies it even more than with a taller gear. What this does is take a similar, or perhaps even smaller amount of torque at a higher rpm, and multiplies it to an even LARGER amount of torque at the wheels, making the vehicle faster.

The supreme example of this would be something like Formula 1. The engine in a modern F1 car produces about 800-850hp at about 18-19,000rpm. This only comes out to a measly 220lb-ft of torque give or take at peak hp. However, with an engine that can turn nearly 20,000rpm(and yes, it IS a piston engine, not a turbine) they have a tremendous range in which they can use to gear the **** out of the car. Now, let's assume they use something like a 4:1 first gear in the trans and a 6:1 differential ratio, that 220lb-ft can be turned into over 5,000lb-ft minus frictional losses, in 1st gear. In all reality, their gearing is prolly even more wound up than that. Final drive ratios in an F1 car's first gear are prolly closer to 20:1(trans gear*diff gear, if they even have a diff, they may use some setup where all the gearing is in the trans but the principle is the same).

Gearing is also why we shift PAST peak torque, and sometimes even past peak hp. When you accelerate you feel the car "pull." The torque that moves the car is pulling you back in the seat(or rather the vehicle is accelerating and inertia is causing your body to try to remain stationary, so really the seat which is attached to the car is pushing into your back). Once you reach peak torque and torque begins to decrease, the vehicle seems like it is no longer pulling, but we REAMAIN in gear. The reason is the vehicle's gearing. Each lower gear has more power multiplication than the next higher gear, and so on and so forth. When we shift up a gear we are losing some of that power multiplica

 

........sounds like a bunch of BS to me.

 

." Higher horsepower engines either are such because combustion pressures are VERY high and rpm remains lower(think deisel engine)" Where does this come from? Diesels are know for massive amounts of torque with minimal HP.