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Im looking a two cars, both are the same model but ones got a 2.0L turbo petrol engine and ones got a 3.0L turbo diesel engine.

These are the full specs

2.0L Petrol

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3.0L Diesel

enter image description here

what im wandering is that although the 0-60 speed is similar the torque is almost 50% more. Ive driven the diesel and what i really liked about its 'effortless' acceleration, is this down to the torque, rather than the speed - if that makes sense ?

sorry if thats a very obvious question my knowledge of physics is 0.

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Their transmissions are probably just geared differently. –  Ben Crowell Jun 12 '13 at 22:56
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3 Answers

The answer to this question is not at all obvious for a number of reasons. Here are a few:

  1. The torque output of an engine depends on the engine RPM at any given instant. This results in a torque curve that looks generically like THIS one.

  2. When the engine torque is quoted, it usually refers to the maximum torque on that curve.

  3. The torque that is delivered to the tires, not the engine torque, more-or-less determines the acceleration of the car at any given instant.

  4. The relationship between the torque output of the engine and the torque delivered to the tires depends on what gear you're in.

  5. The 0-60 time only tells you information about the average acceleration of the car during that time interval.

If you combine all of these things, then you'll see that there is no simple relationship between the max engine torque, and the average acceleration during 0-60. You'd either need to perform a complicated computer model, or just go test the car, to determine what's going to happen given certain figures. That's precisely why they list all of those numbers; you can't easily predict one from the others.

Cheers!

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The figures used in adverts for cars typically show peak torque, as it actually varies over the entire range of engine speeds.

Simply put, torque is what gives you acceleration at low engine revs, but gearing and maximum engine revs are also essential. And in fact drag and other factors come in at higher speeds. And over all that you need to look at the weight of the car, as acceleration = force / mass - despite being the same model, they will have different weights and the gearing will almost certainly be different as diesel and petrol engines have peak torque at different revs.

So from the question there is not enough data to say what is the core component in the case of these two vehicles

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The diesel while having similar max hp as the petrol, will have significantly more hp at 2000 rpm than the petrol. So from 1000 to 4500 rpm the diesel will have significantly more acceleration than the petrol in the same 1000 to 4500 rpm range with equivalent gearing, hence the more effortless acceleration. So in 99% of everyday acceleration scenarios, the diesel will be far more satisfying and peppy. Now if one accelerates 0 to 60 mph at max rpm, where one lets out the clutch at 5000 rpm then the petrol will win that race, but if the same race is conducted with both engines at idle as they normally would be in everyday driving, the diesel will pull far ahead at the start if both cars have equal gearing. So in the cars you mentioned the petrol is putting out 82 hp at 2200 rpm, and the diesel is putting out 120 hp at 2200 rpm. Guess which rpm a car will be closer to most of the time. So 99% of the time the diesel will feel more satisfying and 1 % of the time the petrol will feel more satisfying if you like making a lot of RPMS to impress people.

As someone else put it you have to drive a petrol like you stole it, to get good acceleration.

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You should tie in torque and power into your answer and explain what effect they have and why. –  Brandon Enright Jun 12 '13 at 20:29
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