The Scottish genius
James Watt

http://en.wikipedia.org/wiki/James_Watt

invented 'horsepower'
and he understood that
maximum horsepower is just the rpm spot where the torque of the engine starts going down faster than the rpm is going up.

You stop being an engine 'newbie'
when you understand that
"It is all about Torque"

Here's a tip:
Concentrate on learning how torque affects fuel economy
and then concentrate on how engine friction affects torque.

Guess What?
When you understand those principles
you will 'automatically'
know all about horsepower too.....

 

Seems awfully framiliar to my current physics class lecture (rotational dynamics). I think I might take this post in to my professor and see who really knows what there talking about.lol


Brian

 

Okay correct me if I am wrong in my understanding.
This is simplified for the sake of discussion.

Smaller crankshaft means less torqueand takes more rpms to produce horsepower.
larger crank means more torque and takes less rpms to produce the same horsepower.
rpms+ torque = horsepower

I am assuming that the higher the torque the higher the the heat and friction because of the distance of the rotation.But you have less rpms so that should lower heat and friction.
Which is it ?

I am also assuming that the higher the torque the less fuel or power from the cylinder it takes to move the crank because of the levering effect of the large crank. I would also assume that it would take less fuel because of the lower rpm ranges
Is that true ?

Is this correct or do I have it backwards????

Isn't it horsepower that provideds the enertia to produce the torque ?

Lets say you have a 5.9L diesel and a 8.0L gas engine the 8.0 should be capable of putting out more power because of the size of the cylinders and the amount of fuel that can be used?

Lets take a 5.9 gas and a 8.0gas engine.
Just for simplification lets say at 10rpmthe 8.0 produces 8psi of force to the crank and the 5.9 say 6.0 produces 6psi of force to the crank. the 8.0 is producing 33% more psi than the 6.0.

So if you increase the rpms of the 6.0 by 33% OR if you reduce the circumferance of the crank in the 8.0 by decreasing the torque by 33%you will be putting out the same amount of power ?

What determines the maximum rpm's an engine can run?
Is friction the only limitation?

 

the think that determines the highest an engine can rev is the piston rods, The stronger they are and lighter the faster they can spin without warping or snapping. The cam, and the heads and intake will determine were you produc the most torque and horsepowerr in the rpm ranges. Generally an engine with a smaller stroke will rev higher and generally faster then an engine with a larger stroke. Like for instance an 4.7 liter magnum versus a 5.9 magnum.
I'm not understanding what your saying about the psi thing at the piston. If you thinking that a larger engine produces more pressure, it's not true. You cubic inches do not affect your compression, or compression ratio. Your piston, rod, and head affect compression ratio. The only thing that affects cubic inches is stroke and bore.

 

I repeat this often, but: Horsepower sells vehicles, Torque moves them.

Simply put, Horsepower is work over time, torque is rotational force. HP means little. A new Honda civic with a 1.6l 16 valve engine makes more horsepower than most 318's of the late '70's and 80's, butdo you think it could move a 5,000 pound truck down the highway at 90 MPH?

 

Can one engine be compared to another?

Can the tiny engine in a weed whacker be compared to the huge K98 diesel in an ocean going ship that has a 39 inch diameter piston?

Yes,
engineers in the past have tackled this
and created a measurement called
MEP (mean effective pressure)
that allows you to compare torque produced per displacement.

http://en.wikipedia.org/wiki/Mean_effective_pressure

Then there is the matter of comparing RPMs.
Engineers have agreed that in instead of comparing RPMS it is better to compare how fast the piston is going up and down in the bore, and they usually do it in feet per minute or meters per second.

When you compare engines on MEP and Piston Speed
suddenly the tiny weed wacker running 10,000 rpm and the giant K98 running at 90 RPM and producing over one million ft-lbs of torque start looking 'nearly' the same.

 

Lets see if I can throw my two cents in and help. Last semester I took one of the three physics classes I have to take and we covered torque. Think of torques this way. If you have a wrench on a nut and you push on the end of the wrench you have a force acting on that wrench. As the wrench moves you can multiply the distance moved by the force used to move it. This is work wich is the same as horsepower. Now the force on the wrench is not the same foce on the nut do to it being a lever arm. The force on the nut is the torque. Now inthis case your hand isproducing the force. In the case of a motor the nut is where it all starts. The nut creates the torque which turns the lever and does work. Here is a for instance. Saythe lever is10 meters long (long *** lever). If you apply a torque of 20 then the force at the end of the lever is 4 and the work done in one revolution would be 259 Joules wich translates into HP if you have know the conversion and the time it took for the lever to go around. Know say that lever is 40 meters long then to get the same force on the end you would need a torque of 160 and the work done would be 1174. To get the horsepower out of the work done you need to know the time it took for it to make a revolution. This is all a rough idead of it but I think I'm close. I amybe way off In wich case I should go take physics agina.

 

a good read that starts with Torque
and goes on to many other truck drivetrain, hill climbing and fuel economy things:

http://www.etrucker.com/content/downloads/ccj0302.pdf

 

Okay , simple question. Say you have 2 identical vehicles, one has 200hp and 300lbs tq and the other has 300hp and 200lbs tq. Which one is going to have the best pulling power and which one is going to be the fastest in a drag race till there both topped out??

And both vehicles weigh the exact same and have the same gear ratios etc....

 

The maximum 300 hp vehicle will win acceleration races, unless they are very short ones like 0-30 mph. With the right gear ratios it will also be able to tow more up steep hills. James Watt understood that the point of maximum hp is the rpm to run the engine if you want maximum torque at the output shaft of the transmission attached to that engine.

The 300 ft-lb max torque engined vehicle will be more pleasing to drive the way the typical USA driver does, because high torque engines have more horsepower available in the 1000-2500 rpm range.