KATwo40 wrote:^^^ I have my reservations about that article.
1. They describe torque as lb/ft (rotational force). Then, go on to say that it's more convenient to say ft/lb and continue referring to it in that way. In fact, ft/lb is a measure of force over time, which is totally different.
2. In the comparison between the Cummins diesel and the Honda F1 they state that if torque were the determining factor in winning races (in terms of acceleration) the Cummins would win.
They go on to explain that the Honda F1 would win because of having higher hp over the Cummins.
While this is true, it's not because the Honda had lower torque. It's because the Honda could rev much higher than the Cummins and sustain a broader torque band.
Remember HP = Tq * RPM / 5252.
The Cummins had a max RPM value of 3000, while the Honda had a max RPM value of 17,800.
This comparison is apples to oranges. A real comparison to depict the importance of torque in a race would be to compare two engines, both with X whp, but with varying torque bands.
For instance, take a Honda B series and a Chevy 350 sb. Let's rev them both to 6000rpm limits.
Give the honda a T3/T4 .50 trim with a boost threshold of 4800rpm.
Make the 350sb V8 an all-motor application.
The dyno would show the 350 making more torque in the lower rpm range than the B series engine.
The result? The V8 would have more useable power throughout the rpm band, resulting in better acceleration overall than the B series engine with equivalent HP and less overall torque.
The context of the statement, "Torque wins races, horsepower sells cars" is not to be read as, "Big peak torque numbers are better than big peak horsepower numbers." It should be read as, "Broad torque bands win races."
1. Actually torque is referred to as ft-lbs or lb-ft. It does not use a "/". 1 HP or 33,000 ft-lbs/min is equal to 330 lbs lifted 100 feet in 1 minute. Or even 100 lbs lifted 330 feet in one minute.
2. It's not the broad torque band that matters. You're still looking at the entire graph as a whole. You have to look at each RPM point individually. HP is not a culmination of torque built up over the RPMs. If you make 200 ft-lbs of torque at 4000 RPM in any motor, it will always make 152 HP at 4000 RPM. It doesn't matter what the torque curves look like before or after 4000 RPM. As I said earllier, the HP is a moment in the RPM.
In your example of the turbo motor with a boost threshold of 4800 RPM, if you regeared the transmission to keep revs over 4800 RPM everytime tyou shifted, then it won't matter what the torque/HP curve looks like before 4800 RPM. If its not at those RPM's, it negates that part of the curve entirely.
I'll give you a better example. We'll use theoretical motors with perfectly flat torque curves.
Motor A has 100 ft-lbs of torque from 0 RPM to it's 10,000 RPM redline.
Motor B has 1,000 ft-lbs of torque but revs to only 1,000 RPM.
Motor C makes 50 ft-lbs of torque up to 5,000 RPM, but makes 100 ft-lbs of torque from 5,000 RPM until it's 10,000 RPM redline.
We'll assume Motor B is directly driving the wheels.
Motor A will have to be geared 10:1 to match motor B's performance. Essentially, Motor A would end up making 1,000 ft-lbs of torque though torque multiplication and have the same top speed in that gear. They would accelerate the same.
Motor C on the other hand, if geared 10:1, would accelerate with half the torque at the wheels of the other 2 motors up until 500 wheel RPM. After that the acceleration rate would be the same as the other 2 motors would after 500 wheel RPM. Motor C would be a good deal behind the other 2 cars as it accelerated slower until 500 RPM and it would never catch up.
Here's the key. Lets say these cars are designed for road racing. And give the track they run on, RPM's never fall below 600 RPM. Each car would be able to run the exact same time as acceleration would be equal among them as they all put an equal amount of torque to the ground. But if you were to drag race the cars from a stop, Motor C has to get through 5,000 Engine RPM or 500 Wheel RPM with half the torque of the other 2 cars before it begins to accelerate at the same rate. So it will have lost ground at the beginning of the race. It won't catch up, but after 500 RPM, it will nto lose anymore ground either since they are accelerating at the same rate.
Calculate and compare the HP level at redline for each motor. You'll find they are all the same rating. Yet Motor C is obviously at a disadvantage in certain situations. What my point is here is that The Torque and HP for that matter only apply to the RPM it occurs at. And if the motor never runs at a given RPM for the situation it's in. Real cars have many gears so the only time such a situation would be an issue is in 1st gear. After first gear, it would be expected that the transmission attached to the motor would keep the engine in the higher torque/HP range and would no longer matter hw much torque is available at low RPM's.
In the real world, engines have torque curves that rise to a peak and then fall again. These curves have different characteristics, but essentially all possess this trait. Typically trucks will have a lower peak, shifting the broad portions of the curve to lower RPM's, where as race/high performance motors will shift the peak higher up to better make use of the leverage provided by the transmissions mated to it.
HP is no more than a measure of how effectively the available torque can leverage the drivetrain through the RPM's. Looking at torque alone tells you little about how an engine performs. Without knowing what RPM the torque occurs at, you can't determine how effectively you can use the torque. Torque without RPM's is 0 HP. Torque with more RPM's results in greater HP. A given amount of torque at higher RPM will always be able to put more torque at the wheels than the same amount of torque at a lower RPM. Lower levels of torque at higher RPM, depending on the actual torque figure and RPM difference can make more HP than it does at the torque peak. In fact, Peak HP in just about every motor occurs after the torque peak.
Lets take an 04 350Z for example. 287HP at 6200 RPM and 274 ft-lbs at 4800 RPM. This is 243 ft-lbs at 6200 RPM and 250 HP at 4800 RPM.
Let's gear this so that the wheel RPM is 500 RPM at the peak HP and the peak Tq.
For peak HP, the gear ratio would have to be 12.4:1. For Peak torque, the gear ratio would have to be 9.6:1.
At 500 Wheel RPM, the Wheel torque at peak engine torque RPM would be 2630 ft-lbs(9.6 x 274).
At 500 Wheel RPM, the wheel torque at Peak engine HP RPM would be 3013 ft-lbs(12.4 x 243).
The wheel torque at 500 Wheel RPM is higher at the peak HP than at Peak torque. This will work at any wheel RPM you choose and calculate more. You can also make these comparisons between different motors as well.
In reality, the torque/HP curve does have an affect on overall acceleration, but only from a standpoint of putting down more torque to the wheels over a wide range of RPM's. This is actually more of an issue because we have set gear ratios and to make better use of a transmission's gearing, we need to have reasonably broad power curves. But if you have a CVT transmission, you would put down the most torque at the wheels by keeping the motor running at peak HP and having the CVT constantly change the ratio to accelerate the car while maintaing the peak HP RPM. In theory, buy doing this, you would only need to make power at the peak HP.
Sorry if this is long and maybe a bit convoluted. I was typing this out at work between calls and other distractions. I'll clarify later if need be.
