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Discussion Starter · #1 ·
This is in response to Seano's explanationabout the Sprinter's handling (end of Az's thread on Sprinter excitement).
I've seen the torque curve for the Sprinter but it means nothing to me.
I also undertand the Sprinter has the same engine no matter how big it gets. I'm wondering about the effect of having the extra heater or using the extra air conditioning that are options. I'm wondering about freeway driving and mountainous terrain.
I gather the vehicle won't turn over easily and that's a comfort but does it's maximum speed of 85 also prevent turning over?
Basically, what happens if you stress the torque or reach the max here?
This is off the topic, but since I started the topic I can go off it: I gather that everyone is frustrated that they can't find the kind of vehicle they really want and no manufacturer seems willing to make it. I feel the same way. I want something we can use for errands and take camping, but not an RV that deprives me of the roominess inside. It want a comfortable driving seat (that isn't a lounge chair either). I want something that allows lots of room for two people to sleep (with curtains and screens that don't expose you to the rain). And lots of room for gear. The Sprinter has a lot, but has a way to go too.
Why is it that nobody listens to the consumer or the voter? (This is way off the topic! But what the heck? It's a free country -- sort of!) Feel free to go off the topic in any replies.
 

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Re: What exactly is torque and how does it affect different vehic ... (SleeplessinMilwaukee)

Torque is an actual measurement of twisting force, that is the amount of power making the twisting or turning action. This is the basic unit of measurement of power for all motor vehicles. Horsepower is related, and is actually *calculated* from the measured torque and involves how much work is done over time.
If you've ever driven a diesel, you've experienced a high torque, low horsepower motor. Plenty of grunt to get things moving, not so much top end power for high speed antics.
A racecar has it's bias more towards horsepower since it needs to make it's power in a faster amount of time. Typically, a racecar will be far faster, but won't pull a trailer or a heavy load.
This is greatly simplified, but it's a difficult concept for some to understand. I hope this helps. I'm not sure what you mean by stress the torque, but diesel motors create much the same torque over thier entire powerband, so unless you're in a big hurry, you won't be stressing the motor.
Also keep in mind that it's not simply how many cylinders a motor has. I used to drive a 28' Volvo cab over 4 cylinder turbo diesel. And it would move down the road just fine with a payload of ten tons.
As far as rolling a vehicle over, this is based on a lot of factors. Center of gravity, suspension, body roll, weight transfer, and yes speed. But you can roll a car at 40mph if you do it right. (Or wrong) Speed is not the only factor.
As far as making what the public wants, that's why manufacturers employ clever marketing campaigns... to convince us we need what they can make most profitably. SUVs are a good example. Their popularity is based mostly on image and perception. They are perceived to be rugged, therefore the owner must be tough. At some point, they starting becoming status symbols and after that it was all over. The manufacturers love them because they are basically trucks with different bodies. Very little R&D, very little in the way of manufacturing costs, but they often sell for well over $40k.
I had a cop tell me recently that real men don't drive minivans, they drive SUVs. I laughed and laughed and then explained to him that real men don't define themselves by what kind of car they drive. And then I laughed some more. But this is an example of how people buy into fads and marketing hype and how this can drive the market.
Az
 

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Discussion Starter · #3 ·
Re: What exactly is torque and how does it affect different vehic ... (Az Barber)

quote:[HR][/HR]
If you've ever driven a diesel[HR][/HR]​
We have a Mercedes Turbo Diesel. So I understand what you mean. It takes longer to get going, but once it's going....it just keeps going. And the turbo part helps with passing. I think the Sprinter also has a turbo element. I'm not into high speed antics, so it sounds like I'd have enough torque for my purposes. (I can't imagine I'd put weight in the vehicle like Fed Ex does with theirs and they have the longest wheelbases on theirs I think.)
My question about "stress the torque" was related to Seano's comment in your post about the engine somehow being stressed if you've got a lot of gear in the van. Since I didn't understand what he was getting at -- and didn't want to get off your topic too far, I just started another one here. I think you basically reassured me, though, that there aren't reasons to worry about the engine's ability to pull the load of the van. I'm assuming that also means that if you're going up a hill, it just keeps going, without losing much speed.
The comment about rolling over was related to Seano's comments again. By his report it sounds like the ride is more stiff but that prevents the van from rolling. I also assume the lower roof would be better (safer), depending on the wheelbase -- lower center of gravity and so on.
You've answered my question about both consumers and voters. They (manufacturers and politicians) want to sell you on their ideas rather than listen to yours. It's now gone beyond convincing "we the people" of their policies; now the whole world should be convinced and fall in line too!
Back to the Sprinter: I suppose the ride not being as comfortable as a sedan or some kind of luxury van won't matter so much if you're on vacation and can take your time getting places, not driving too many hours a day and so on. Or for just city driving on errands. The Sprinter seems like a practical solution.
The fact that you like this vehicle (given your knowledge about so much related to cars and trucks and engines and so on) says a lot about it. In addition to its spaciousness and the diesel engine, which is big plus for mileage and durability. I also love seats that allow you to have your legs vertical rather than horizontal (which is very bad ergonomics for the body).
My fear here is that they will take something that looks pretty suitable now and tinker with it till it becomes something no one is happy with. (By trying to make it "exciting" so they can advertise it as such! -- thereby losing all its practicality!)
 

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Re: What exactly is torque and how does it affect different vehic ... (SleeplessinMilwaukee)

The old addage is "horsepower is what you read about, torque is what you feel". That is why small displacement high horsepower Japanese cars don't feel that impressive, even though they have lots of HP, they don't have any torque down low where you feel it.
quote:[HR][/HR]
The comment about rolling over was related to Seano's comments again. By his report it sounds like the ride is more stiff but that prevents the van from rolling. I also assume the lower roof would be better (safer), depending on the wheelbase -- lower center of gravity and so on.
[HR][/HR]​
What I think Seano was saying when he was referring to "roll" was not "roll over" but the "roll stiffness" of the van, in other words, lean in cornering.
 

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Re: What exactly is torque and how does it affect different vehic ... (Az Barber)

Be careful mixing Torque and Power -- torque is not a measurement of power, horsepower is a measurement of power. In fact power is essentially torque times engine speed... or torque @ speed.
The way I always think about it is that a car needs a given amount of torque to get up a hill to just lift its weight, but power is what gets the car up the hill faster. So if two vans go up that hill and one does it twice as fast, the faster one is producing twice the horsepower at the wheels.
Jeff
 

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Re: What exactly is torque and how does it affect different vehic ... (J_Westy)

quote:[HR][/HR]Be careful mixing Torque and Power -- torque is not a measurement of power, horsepower is a measurement of power. In fact power is essentially torque times engine speed... or torque @ speed.[HR][/HR]​
Actually, you have it a bit backwards. As a pro dragracer, mechanic and certified dyno tech, I have long since learned the relationships of torque, horsepower, speed, and acceleration.
First hint: Torque and horsepower are very closely related. In fact, for motors that reach redline somewhere between 5 and 6k rpms, they are going to be *very* closely related. Torque and horsepower are *always exactly the same* at 5252 rpms. Assuming a redline of 5500 for example, if you increase the torque at 5500 rpms, you will also increase horsepower a very similar amount.
And as far as measurement goes, every dyno in the world, whether it's an inertia dyno, brake dyno or water dyno measures *torque*. Horsepower is then calculated from the torque produced using the formula H=T x rpms/5252. It doesn't make any difference if you measure it at the crank or at the wheel, this is the way horsepower is calculated. Horsepower is an abstract and cannot be measured. This is sort of like seeing gravity. You can see the effect, but you can't see the force itself.
quote:[HR][/HR]The way I always think about it is that a car needs a given amount of torque to get up a hill to just lift its weight, but power is what gets the car up the hill faster. So if two vans go up that hill and one does it twice as fast, the faster one is producing twice the horsepower at the wheels.
Jeff[HR][/HR]​
Torque is the moment of inertia, horsepower is the work over time. Depending on the vehicles and the grade of the hill, a vehicle with a higher torque rating could easily make it up the hill faster than another vehicle with less torque. But then again, in the real world if the first vehicle is making more torque, it's most likely making more horsepower. The exceptions would be very low revving motors, like diesels, and very high revving motors, like F1 motors that rev to 16k rpms.
Az


[Modified by Az Barber, 5:20 AM 1-25-2003]
 

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Re: What exactly is torque and how does it affect different vehic ... (Az Barber)

quote:[HR][/HR]Torque is an actual measurement of twisting force, that is the amount of power making the twisting or turning action. This is the basic unit of measurement of power for all motor vehicles. [HR][/HR]​
No offense Az, but I don't think I have it backwards. I think we're saying the same thing. I was only commenting that Torque is not a measurement of power.
I think if you think about my hill analogy a little more, you'll realize it's correct.
Here's another one that you might like?
. What accelerates a vehicle is really excess torque. F = ma, so a = F/m. And F = T_axle * radius of the tire.
Jeff
 

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Re: What exactly is torque and how does it affect different vehic ... (J_Westy)

These torque/horsepower discussions are always fun to follow! I can't help but jump in.
As already correctly stated, HP is torque times rpm divided by 5252. My 98 New Beetle TDI I used to have felt MUCH more powerful than the 90 hp, 145 ft-lbs rating. The 2.0 L gas engine in the Beetle had 120 hp and less torque than the diesel. 1/4 mile times were almost identical between the two engines, and in normal driving the diesel felt much quicker. The gas engine has to scream over 6000 rpm to get all 120 hp, so that power is not as easily available. In normal driving the TDI had more available hp from idle to 4000 rpm, that's why it felt so good versus the gas engine.
When comparing the power curves, the TDI had more HP (and torque) than the gas engine up to about 4000 rpm, after which the gas engine made more power. More torque at a certain rpm always means more hp at that same rpm. That impressive acceleration you feel at low to mid rpms with turbo diesels means it is making more hp than a comparrable gas engine, at that same rpm, because it is making more torque. With enough gear reduction (and time), a lawn mower engine can pull a van to the top of a hill, providing sufficient drive wheel torque, or tractive effort, but very little hp.
Torque is telling you how big the bang in the cylinder is. HP is essentially how many big bangs can you get in a unit of time.
An engine that could make 500 lb ft of torqe might sound great, but what if redline was only 1000 rpm? That's only 95 hp. It really comes down to HP, if you're interested in how quickly a vehicle will accelerate or go up a hill, or top speed. You can also look at tractive effort, which only looks at torque and gear ratios, but, more torque again means more hp. It just comes down to hp.
Here's something to ponder. We've all heard that long stroke engines make more torque. More leverage on the crank for increased twisting force. If you look at two engines of identical displacement, one with a long stroke small bore and the other with a short stroke and big bore, they will make about the same torque. The smaller bore means less area for the combustion pressure to push down the piston, but the lever arm is longer. The big bore means more piston area, so more force is applied to push down the piston, but the shorter lever arm cancels that out. It all cancels out.
The peak HP potential of the big bore engine is greater than the short bore, because of the increased space for larger valves, and the fact that the engine can be revved higher to utilize that valve area since piston speeds are reduced comparred to the long stroke. Torque is basically proportional to displacement (and boost!), while HP potential is proportional to bore dia, or valve area.
Those small high revving engines don't make much torque, becuase they don't have much displacement. But, since they can spin to a high rpm they make good hp, utilizing that valve area from 4-5 valves. You just have to work hard to get it.
 

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Re: What exactly is torque and how does it affect different vehic ... (BMEP)

quote:[HR][/HR]
An engine that could make 500 lb ft of torque might sound great, but what if redline was only 1000 rpm? That's only 95 hp. It really comes down to HP, if you're interested in how quickly a vehicle will accelerate or go up a hill, or top speed. You can also look at tractive effort, which only looks at torque and gear ratios, but, more torque again means more hp. It just comes down to hp.
[HR][/HR]​
Again no offense, but there's nothing in my two posts above that's wrong... It's hard to put ones arms around this because everyone forgets about the gearbox. Hp is a convenient measure because (ignoring losses in the gearbox) the Hp at the engine is the same as the Hp at the axle. Torque on the other hand is ratio'ed by the gearbox.
If one vehicle goes up hill twice as fast as another, the faster on is putting out twice the Power. They're both putting out the same torque at the axle (ignoring the extra torque to overcome the added wind resistance on the faster vehicle) to lift the vehicles up the hill, and as Az and BMEP have restated, P = T * rpm, so if the axle is spinning twice as fast, there's twice the Hp.
With respect to the excess torque is what accelerates the vehicle. I think if you think about it more you'll see it's also correct. F = ma, so a = F/m. And F = T_axle * radius of the tire. This is an instantaneous equation, but it's correct. There's more to it if you're talking about 1/4 mile times... like the inertia of the engine, gearbox and driveline; the gear and axle ratios; etc.
Jeff
 
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