I apologize.
I am not very gifted for teaching or sharing explanation.

Let me try all over again, and I try to keep it as simple math as possible.
I intend to show that the best performance (acceleration) of a car, be it diesel or petrol, is achieved when keeping the engine in its rev range of max power, and well above the revs of max torque.

Let's take a concrete exemple: an RS TDI driven at 100km/h (62mph).
Based on the wheel radius, this correspond to a wheel angular speed of ~860rpm.
We want now to apply the max possible acceleration to this car, thus the max possible torque to this wheel.
We can do this using several possible gears.

Let's try in third gear:
Based on the axle ratio and 3rd gear ratio, a 860rpm wheel rotational speed requires the engine revs to be ~3920rpm.
We need the engine to be at max load, so 3920rpm corresponds to a 135kW engine power and a 325Nm engine torque.
The transmission ratio as above translates the 325Nm engine torque into a max applicable torque at wheel of 1255Nm.
(note that the power at wheel is then the max engine power).

You can repeat the computation from 4th to 6th gear with the following result:

 

 

Here we can see the max torque applicable to the wheel (thus the max acceleration) is achieved with 3rd gear,
when engine revs is in the max power range and when engine torque is below the max engine torque value.
The same can be repeated with different car speed values.
The result is given below:

 

 

This table shows that whatever the car speed, the max acceleration is always achieved with a gear making the engine revs above the max engine torque revs (3000rpm), and always close or within the max engine power revs range (from 3500 to 4000rpm).
This is always the case when the gearbox is well tuned for the engine characteristics.

Going one step further, you can do the comparison with another car having the same max engine power, with a completely different max engine torque value.
Let's take the 1.8 TSI 180hp, with 250Nm max engine torque.
Of course the gearbox ratios are different.

The computation show the results below.

 

 

Despite significantly lower value for max engine torque, the torque applicable at wheel is more or less the same between the two cars, leading to the same moving force.
I don't discuss here other parameters that might impact the acceleration (weight, drag, ...) but only the engine characteristics.

The conclusion is the max engine power remains the best indicator for a car performance, and the engine max torque value alone doesn't say a lot.

And you have to use the engine within its max power range for reaching the max possible performances.
I don't debate the fact that many people may prefer driving on the engine torque on the dayly life rather than going up in revs.
 
But even here, preconceptions might be deceiving: thanks to a very suitable gearbox, the 1.8 TSI engine brings more torque to the wheels in 6th gear than the RS TDI up to 80km/h. (or in 5th gear below 60km/h).

Edited 1 December, 201510 yr by JPH0091

I would say that car 'bites' as long as You are pulled to back od the seat, means You got acceleration, right?

I am no racer, but on vRS it stops brutally after ~3.000rpm, so it's a good time to shift or You will loose that momentum in next gear.

Diesels are always ''driven by torque" and they got them plenty in low rev's, quite opposite as the petrol engines which will most likely hesistate or even stall if You hit them hard at only 1.500rpm. But that rev range is usually a starting point for turbo spinup and where the fun starts on diesel.

No offence, but I need no formula or torque chart for that :-)

Just a few miles of normal drive and I simply know what engine can do.

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+1 exactly what I have found on every turbo diesel I have driven

With the TDI 184 it has pretty severe lag below 1500rpm...no doubt down to it having a reasonably large turbo....something that VNT and e-wastegate tech cant entirely eradicate...nature of the beast with a lowish capacity high output 4 cyl TDI.

To make swift progress without driving it hard you simply need to keep the revs between 1750 and 2750rpm as its the TDI's peak torque sweetspot.

To make it go as fast as possible you have to rev it hard to at least 3750rpm in each gea as that is bang in the middle of its peak power....its not unreasonable to rev it to 4 - 4.2k if driving it flat out though its power tails off noticeably after its 4k rpm peak.

There is an art to driving a TDI quickly....given the new engines arent stereotypically diesel-like in that they like to rev (for a diesel) there is a bit of readjusting required (from a PD engined vehicle where you get the best from it by riding the huge wallop of low down torque and short shifting).

I know for certain my GTD is far keener off the mark if the ESC reigns are loosened.....its quicker in and out of corners too providing you can drive a bit and modulate the throttle well (as so not to light the tyres up exiting a corner).

Trying to thump 280lb/ft of torque through a cars front wheels from not far beyond idle into its mid range without some electronic interference and no proper diff would make the car borderline undriveable in all bar the dryest conditions if you have a lead foot....the car noticeably reigns in its go in 1st and 2nd when ESC is fully enabled in the dry and wet.

Even in ESC sport the car will try to curb 2nd gear wheelspin.

So in summary....the diesel isnt as quick as the petrol (but we all know that)....but its still bloody quick if you know how to drive it to extract the best from it. Drive it like an old school diesel with all the electronic aids on it, it will feel quite disappointing.....rev the thing and turn down the aids its rather engaging...as engaging as a 4cy 2.0 diesel can be anyway.

Edited 1 December, 201510 yr by pipsypreturns

Makes me laugh the whole "TDI isnt a proper vRS just a trim level" attitude.

Its the same f-ing car as the TSI, just with a slightly less powerful diesel motor trading some all out performance for better running costs which suits most people wierdly enough as they are in the main bought as family cars or run as company cars...the latter a diesel cetainly makes way more sense unless you get kicks throwing cash at the tax man.

Lets face it the TDI can still dispatch 60 in less than 8 secs (lets ignore the book figures as we all know they are *******s) and run onto well over 140mph.....I dont classify that as lacking performance...particularly when it can return 50-odd MPG all day long.

Its doesnt change the fact that vrs tdi is the slowest of the 3 versions of 184TDI(vrs, 4x4 and Scout). The normal 184 4x4 is over a second faster in the only official benchmark available (0-100kmh). Its even faster than the vrs tdi 4x4.

160 hp/ton Vs 132 (TSI Vs TDI). Almost 20% difference.... I'm going to go for the not a proper VRS attitude.

And while we're at it, a TDI VRS has only 11% more hp/ton that a 150HP elegance, so yep..... a trim level.

hOw is it just trim? bOth are identical suspension and steeringwise, the two pipes exhaust on the tsi is just looks, as it tees off near the fuel tank, does not add to its performance in the way a twin pipe does on a v block engine, yes the tdi is slower, but are both vrs',both have pros n cons, a true performance petrol engined car would leave both standing like a sack of sh 1te,

Edited 3 December, 201510 yr by cortina63

Its doesnt change the fact that vrs tdi is the slowest of the 3 versions of 184TDI(vrs, 4x4 and Scout). The normal 184 4x4 is over a second faster in the only official benchmark available (0-100kmh). Its even faster than the vrs tdi 4x4.

Many of VAGs official figures are nonsense.

I have a GTD...Ive no doubt launched perfectly it'd get to 100kph in about 7 secs....might not be terribly easy to replicate again and again but its definitely capable of bettering its official 7.5 sec book figure.

Same for the vRS.....if the GTD and Leon can get to 100 in 7.5secs....why is the Skoda 0.6 seconds slower...other than being longer weight wise there is little or nothing in it.....I am sure they share the same gearbox ratios etc so I have no doubt at all a vRS can comfortably break 100 in far less than 8 secs.

Also 0-100 sprints only tell a v small part of the story.....once you are off the line the traction advantages of 4wd (other than entry/exit cornering speeds) are meaningless...where there is no tractio issue the additional weight and associated parasitic power losses of the 4wd provw the car with a (v slightly) inferior power to weight ratio.....the difference would be negigable but id wager at a dig at say 80mph in 6th a 2wd car would pull away slightly as the motor is overcoming less weight.

Anyway all moot points. Like a GTI/GTD/R is quite different in its make-up to a regular Golf (i.e not just a spec level), same goes for the vRS as it is v heavily based on the GTI and GTD sharing much of the associated hardware componentry.

The comments about the exhaust arrangements between the two cars being made (not by you) are quite futile....the TSI and TDI motors have completely different exhaust systems....why the GTI and GTD Golfs have a different rear arrangement. It would have cost money to delevelop a corner to corner exit rear section for the TDI cars so of course they didnt bother. In the case of the vRS they obviously wanted the petrol and diesels to look identical and it again was cheaper to go with the faux exhausts and hide the real exhausts behind the bumper.