Torquing about Torque...
Discussion
I'm curious. I think I've got my head around the notion of torque, at least as far as the myriad posts here and elsewhere on the subject (resorting on occasion to complicated equations of motion and energy the like of which rarely make it out of undergrad physics and engineering textbooks)...
Anyway, it seems that diesels generally have wallops of torque (e.g. the 330d with 410Nm) whereas the petrols have more power and less torque (e.g. 230bhp versus 200bhp being typical).
What I'm wondering today, in the second in my series of automotive navel-gazes, is whether one car suits a particular style of driving over another. For instance, if you're a revver, I reckon a petrol engine is going to move quicker, but if you like being lazy (as I do), then the low-down torque of the diesel motor might make it quicker for every-day driving.
Am I right in thinking this? In which case, for 30-70mph '4th gear-ish' manœvures, would a highly torqued or even remapped 330d be quicker than a 330Ci?
Disclaimer: I have no intention of thrashing my motor around a racing track - I'd rather leave that to the boy-racers and the serious racer-wannabes. Me, I can't see a car like this (330anything) as being remotely race-able, so I wouldn't expect to be needing out-and-out 'at-the-end-of-its-range' revability, but it would be quite nice not to have to worry about what gear I'm in if I want to pop past an annoying volvo sitting at 45mph in a 60mph zone.
So, humour me, I'm all ears...
Anyway, it seems that diesels generally have wallops of torque (e.g. the 330d with 410Nm) whereas the petrols have more power and less torque (e.g. 230bhp versus 200bhp being typical).
What I'm wondering today, in the second in my series of automotive navel-gazes, is whether one car suits a particular style of driving over another. For instance, if you're a revver, I reckon a petrol engine is going to move quicker, but if you like being lazy (as I do), then the low-down torque of the diesel motor might make it quicker for every-day driving.
Am I right in thinking this? In which case, for 30-70mph '4th gear-ish' manœvures, would a highly torqued or even remapped 330d be quicker than a 330Ci?
Disclaimer: I have no intention of thrashing my motor around a racing track - I'd rather leave that to the boy-racers and the serious racer-wannabes. Me, I can't see a car like this (330anything) as being remotely race-able, so I wouldn't expect to be needing out-and-out 'at-the-end-of-its-range' revability, but it would be quite nice not to have to worry about what gear I'm in if I want to pop past an annoying volvo sitting at 45mph in a 60mph zone.
So, humour me, I'm all ears...
having never been in a 330i when it's been floored in a high gear with not many rpm i can't say what it will be like (i have been in a 330ci being floored in a low gear though 
), but i have been in a 330d being floored in 5th-6th gear from not many mph and can say it's quite amazing. for the relaxed, overtaking in any gear driving style, i would be inclined to say yes, a 330d would be quicker. unfortunately you don't get a lovely 6 cylinder petrol noise though! but having spent many thousand miles in an e46 330d i can honestly say it's many moons away from the tractor people say all diesels are.
a tough choice, but it's a good choice to have to make, as they say.
hope this helps some what.
), but i have been in a 330d being floored in 5th-6th gear from not many mph and can say it's quite amazing. for the relaxed, overtaking in any gear driving style, i would be inclined to say yes, a 330d would be quicker. unfortunately you don't get a lovely 6 cylinder petrol noise though! but having spent many thousand miles in an e46 330d i can honestly say it's many moons away from the tractor people say all diesels are.a tough choice, but it's a good choice to have to make, as they say.
hope this helps some what.
At the end of the day, ultimate performance is far more closely related to power than torque, most 200bhp cars of similar weight will accelerate at a similar rate regardless of diesel or petrol, but the same can't be said of most cars of the same weight with say 200 lbft peak torque output.
Torque at the wheels is what really makes you accelerate, the amount of turning force at the tyre contact patch. That's related to the engine torque but also directly related to the gearing, the lower geared the car is, the more torque at the wheels for a given engine torque. If an engine can't rev very high (i.e. a diesel), it can't have low gearing without being unusable in normal driving, and likewise if an engine can rev but produces relatively low torque (the petrol), it can't be geared too high because it couldnt pull the tall gears.
Diesels are generally better for when you're driving "lazily" though because more often than not the revs that give you peak (or near peak) performance are closer to the revs you drive at normally anyway, so you don't have to change down so often and extend it so much to extract useable acceleration. For example, a diesel might be crusing at 70mph in top gear revving at 2000rpm, which coincides with peak torque, so put your foot down and there's reasonable performance on tap. An equivalent petrol car might be cruising the same speed at say 2500rpm in top so its 20% lower geared (an advantage), but its peak torque is say 40% lower (big disadvantage) and isn't available until 3500rpm so actual available engine torque might be 50% lower at this point. Because of those factors, there's a lot less torque at the wheels at this point, so plant your foot without changing gear and comparatively not a lot happens. Change down in the petrol though and you've now multiplied up that engine torque so it can compete with the diesel for acceleration. You could gear the petrol to also cruise at peak torque and overcome some of that disadvantage, but that would be akin to sitting in 4th gear on the motorway so it would use a lot more fuel and be less refined when cruising etc.
In gear times are sometimes a little misleading though because some of them you wouldnt use in the real world and for a given speed increment, a petrol can generally do it a gear lower than an equivalent diesel. Take 4th gear 50-75 for example, my 200bhp diesel (a 123d) couldn't do that in 3rd so 4th is the optimum gear to accelerate for that test, but a 130i petrol could do it in 3rd so to compare the 130's 50-75 in 4th is a little unfair because if you were going to overtake someone doing 50mph you'd select 4th in mine or 3rd in a 130. In gear acceleration in top is possibly more relevant because it shows what you can do without having to change gear at all, as does 30-70 through the gears because it allows each car to use its optimum gears.
Torque at the wheels is what really makes you accelerate, the amount of turning force at the tyre contact patch. That's related to the engine torque but also directly related to the gearing, the lower geared the car is, the more torque at the wheels for a given engine torque. If an engine can't rev very high (i.e. a diesel), it can't have low gearing without being unusable in normal driving, and likewise if an engine can rev but produces relatively low torque (the petrol), it can't be geared too high because it couldnt pull the tall gears.
Diesels are generally better for when you're driving "lazily" though because more often than not the revs that give you peak (or near peak) performance are closer to the revs you drive at normally anyway, so you don't have to change down so often and extend it so much to extract useable acceleration. For example, a diesel might be crusing at 70mph in top gear revving at 2000rpm, which coincides with peak torque, so put your foot down and there's reasonable performance on tap. An equivalent petrol car might be cruising the same speed at say 2500rpm in top so its 20% lower geared (an advantage), but its peak torque is say 40% lower (big disadvantage) and isn't available until 3500rpm so actual available engine torque might be 50% lower at this point. Because of those factors, there's a lot less torque at the wheels at this point, so plant your foot without changing gear and comparatively not a lot happens. Change down in the petrol though and you've now multiplied up that engine torque so it can compete with the diesel for acceleration. You could gear the petrol to also cruise at peak torque and overcome some of that disadvantage, but that would be akin to sitting in 4th gear on the motorway so it would use a lot more fuel and be less refined when cruising etc.
In gear times are sometimes a little misleading though because some of them you wouldnt use in the real world and for a given speed increment, a petrol can generally do it a gear lower than an equivalent diesel. Take 4th gear 50-75 for example, my 200bhp diesel (a 123d) couldn't do that in 3rd so 4th is the optimum gear to accelerate for that test, but a 130i petrol could do it in 3rd so to compare the 130's 50-75 in 4th is a little unfair because if you were going to overtake someone doing 50mph you'd select 4th in mine or 3rd in a 130. In gear acceleration in top is possibly more relevant because it shows what you can do without having to change gear at all, as does 30-70 through the gears because it allows each car to use its optimum gears.
Edited by LocoBlade on Sunday 22 March 19:38
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