Thanks guys for explanations! Some of the example really helped to understand the practical side of it

I asked this question in the context of looking at ML350 and ML320 CDI. I will be test-driving the latter today or tomorrow. I wanted to set expectations right.

The last time I drove a turbodiesel, it was a new Land Cruiser and I was not too much impressed. We'll see what ML320 CDI has to offer.

 

If your clutch holds up, you will reach warp speed, or your clutch will vaporize with the explosive force of an atomic bomb.

 

This is a total nerd explanation, and assumes exact same car except the engine output:

If you are asking for the specific theoretical physics view, it is the same for all 3 questions. All else equal, and assuming no traction slipping, the acceleration potential from a stop or roll makes no difference between car setups. They are going to perform to their performance specs. Of course in the real world at some point you do consider traction loss when viewing a launch from a stop when the torque put down is too high for traction.

Torque is a Force, and i believe the term in physics for horsepower is "Power" or Work over a certain Time frame. You can wikipedia them if you want to know the book definition.
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The acceleration rate for any car will be the effective torque at the wheels after gearing at any specific point in time, and theoretically will follow the effective torque curve (at the wheels, with gearing taken into account) to the letter. There is no reference to a period of time or distance here, we are simply saying all else equal more Force = higher acceleration at a given moment of time.

For your question, all else equal, if there is more effective torque at the wheels in one car, it will out accelerate the other at that point of time. To compare for a period of time or distance see below:

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You can only truly compare two engine setups by having the full torque curve, and the gear ratio information, so you can calculate the effective at the wheel numbers.

To compare a between two car setups for a period of time or distance, you can chart the Effective HP@ wheels/MPH for each gear for each car, and create one curve for each car at each gear's crossover point (optimal shift points).

Comparing these two curves will tell you how quick each car will accelerate at any specific speed relative to the other. This is because HP is derived from torque and engine speed. This is still a single point comparison, not a period. To compare how which will reach a speed faster (0-60mph) you integrate (calculus) the area under the curve from for any range to compare which will be faster over the same period, where the one a higher figure or area will reach it sooner.

If you want to compare over distance, or some other measure, you convert the variables on the charts to what you want (i.e. HP / distance)

 

Well, to my knowledge, torque is what gets you to speed while more horsepower will give you a higher top end. You can accelerate harder as your torque curve raises, but that won't be the case with hp.



But the op's question makes no sense to me. Good torque on the low end does nothing for any car. Mid end torque like our G's is what you want.

But if we're comparing two cars, one with lots of horses and not so much torque vs a car with lots of torque, not so much hp... then the higher torque car will take the lead from the start with it's faster acceleration while the high horsepower car catches up towards the end with it's higher top speed.

 

This is why a low horsepower hybrid can be very fast 0-60. The electric motor while not very powerful, can produce full torque from time zero, which an IC engine cannot.

 

Well why didn't you say so! Easy: both will be as slow as watching paint dry.

Apart from the poking of fun, post #2 is a pretty good explanation of it. It's all about area under the curve from a dig, and when you're to the top end of the rpm range, area under the curve for that rpm "spread" between gears.

Ideally, you want more torque at higher rpm ranges to make the most horsepower. Horsepower is torque at an applied rate.

But that's for drag racing, which will be hilarious in either ML. Practically, I'd go for the diesel because they tend to be bulletproof, last forever, and have plenty of torque for hauling a heavier vehicle, lots of people/luggage, or towing something lighter. At least around here, diesel fuel tends to be marginally cheaper than 87.