I’m thinking of a sports car vs. tow truck. An engine built for speed, and an engine built for power (torque). How do the engines react differently under extreme conditions? I.e being pushed to the max. What’s built different? Etc.
In: 3108
Dear God, the answers here are terrible.
The short answer is that there’s not a difference.
Powerful engines have high power output, meaning horsepower. Torque is a measure of angular force, which means force of twist, or how hard it twists.
Horsepower is, mathematically, torque multiplied by revolutions per minute divided by 5252 (just trust the constant, the explanation isn’t relevant for this).
So how to you get high horsepower? You use high torque or you have high rpms. High rpms mean more movement, which means more friction and less efficiency.
Higher torque means the engine has to be able to take higher internal forces (since torque IS rotational force), which means it’s heavier. Heavier is often bad for a race car.
So the answers about diesel being heavier, but making more torque are right then, right? I’m mad over nothing!
Well, no.
Let’s look at the most prolific engine family of all time, the Chevy small block. Specifically, let’s look at the 3rd and 4th gen, the LS family.
The same engines were routinely used BOTH in trucks and Corvettes. Sure, they’d get tweaks to push the horsepower a bit higher in the Corvette, or a bit more low end torque for the LQ (truck designated) engines, but they’re ALMOST identical. So what gives?
The definition of torque. That’s what.
Torque is force at some distance from the centerline. Basically, if you put a 1lb weight on an arm 1 ft long, you have 1 ft-lb of twist. If you double the length? The same 1 lb is now doing 2ft-lb of twist.
So how’s the Corvette, a high performance sports car, using a truck motor that doesn’t rev very high? One word: gearing.
ANY engine can have ANY torque value at the tires, which is where it’s measured. As Archimedes said, give me a long enough lever, and a fulcrum on which to place it, and I will move the world.
Any engine can be a race car engine. Any engine can be a truck engine. The energy output per second, or power, is all that matters. With gears, you can reshape your power to be used however you need, speed or grunt.
So why do semis use diesel? Because it’s cheaper. That’s it. Diesel is cheaper per used power because diesel is more power dense than gasoline. The higher compression ratio is more efficient. Glow plugs last longer than spark plugs. Diesel engines last longer and are simpler to repair when they do fail.
The claims on shorter piston movements meaning more power but less efficiency? True, because of friction losses in longer strokes with higher RPM. That higher RPM, we we saw in the equation, means more power.
TL;DR: there’s virtually no difference in the engines. The transmissions are where the differences are. Diesels are used because they’re efficient and reliable.
Edit: promptly a complaint about not using metric, so here you go: Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488
If you’d rather use a multiplier of 1/9.5488 instead of 1/5252, be my guest. You can similarly use 1N of force on a 1m and 2m bar, etc. I don’t care. After a decade as an aerospace engineer, I don’t particularly care what anyone’s using.
I’m thinking of a sports car vs. tow truck. An engine built for speed, and an engine built for power (torque). How do the engines react differently under extreme conditions? I.e being pushed to the max. What’s built different? Etc.
In: 3108
Dear God, the answers here are terrible.
The short answer is that there’s not a difference.
Powerful engines have high power output, meaning horsepower. Torque is a measure of angular force, which means force of twist, or how hard it twists.
Horsepower is, mathematically, torque multiplied by revolutions per minute divided by 5252 (just trust the constant, the explanation isn’t relevant for this).
So how to you get high horsepower? You use high torque or you have high rpms. High rpms mean more movement, which means more friction and less efficiency.
Higher torque means the engine has to be able to take higher internal forces (since torque IS rotational force), which means it’s heavier. Heavier is often bad for a race car.
So the answers about diesel being heavier, but making more torque are right then, right? I’m mad over nothing!
Well, no.
Let’s look at the most prolific engine family of all time, the Chevy small block. Specifically, let’s look at the 3rd and 4th gen, the LS family.
The same engines were routinely used BOTH in trucks and Corvettes. Sure, they’d get tweaks to push the horsepower a bit higher in the Corvette, or a bit more low end torque for the LQ (truck designated) engines, but they’re ALMOST identical. So what gives?
The definition of torque. That’s what.
Torque is force at some distance from the centerline. Basically, if you put a 1lb weight on an arm 1 ft long, you have 1 ft-lb of twist. If you double the length? The same 1 lb is now doing 2ft-lb of twist.
So how’s the Corvette, a high performance sports car, using a truck motor that doesn’t rev very high? One word: gearing.
ANY engine can have ANY torque value at the tires, which is where it’s measured. As Archimedes said, give me a long enough lever, and a fulcrum on which to place it, and I will move the world.
Any engine can be a race car engine. Any engine can be a truck engine. The energy output per second, or power, is all that matters. With gears, you can reshape your power to be used however you need, speed or grunt.
So why do semis use diesel? Because it’s cheaper. That’s it. Diesel is cheaper per used power because diesel is more power dense than gasoline. The higher compression ratio is more efficient. Glow plugs last longer than spark plugs. Diesel engines last longer and are simpler to repair when they do fail.
The claims on shorter piston movements meaning more power but less efficiency? True, because of friction losses in longer strokes with higher RPM. That higher RPM, we we saw in the equation, means more power.
TL;DR: there’s virtually no difference in the engines. The transmissions are where the differences are. Diesels are used because they’re efficient and reliable.
Edit: promptly a complaint about not using metric, so here you go: Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488
If you’d rather use a multiplier of 1/9.5488 instead of 1/5252, be my guest. You can similarly use 1N of force on a 1m and 2m bar, etc. I don’t care. After a decade as an aerospace engineer, I don’t particularly care what anyone’s using.
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