it's the torque that explains why the cars are different performance wise - not the horsepower
I'm definitely not looking at the wrong numbers, the mistake would be making that decision based purely on numbers and outadated "petrol vs TDI performance" arguments from 10 years ago: I was using the numbers to try to quantify the shape and scale of the torque and power curves.
If the "performance wise" you're talking about is the accelleration, then there is a fundamental fact that accelleration (assuming similar traction and weights) would be based on power, not torque. Power is just a factor of torque x revs, but the power is the overiding part of that equation and even more importantly average power, NOT peak power... my old V6 TDI had more torque than a B7 RS4... but I knew which was faster
That said, the 3.0TDI vs 3.2 petrol with similar peak power, the TDI was faster - 10+ years ago I was pushing the "TDI is best" side of the debate, but the game has changed...
What I think you're trying to grasp at is the old argument about the shape of torque curves and it has already been debated and analysed AT LENGTH with the old Mk4 generation Golf GTI, where the car was conveniently available in 4 engines over the course of it's lifecycle: 115bhp 2.0i, 140bhp 1.8i, 150bhp 1.8T and 150bhp 1.9TDI... in this case the peaky 1.8 N/A was noticably slower than even the 2.0i as it only generated the peak power for a really narrow part of the rev range. This is the argument that I was having with people about TDI vs petrol from 2000 onwards - for most, the TDI's were hands-down the better cars, but this argument has gone full circle as a lot of petrol cars are turbo/super/"twin"-charged. The TDI's still win on economy, but NOT performance: even highly tuned with two turbo chargers, they struggle against a detuned, supercharged petrol and even with just a basic remap on each, you won't unock much more on the BiTDI, but you will get rid of the dutuning on the TFSI (to protect the S5 and S6) and then the TFSI thrashes the BiTDI.
In the old TDI vs petrol performance debate, TDI won a lot of the time because it was actually a N/A vs forced induction debate and the "area under the curve" is greater in forced induction engines the same peak power. So this effectively means that at any point when accelerating through the required rev range for each gear, you are more likely to be at a higher power level, in the case of turbo-charged engines this assumes you are already accelerating hard and have the boost pressure ready or are willing to wait for it to spool up... the rest of that sensation of speed in a turbo-charged car is down to just that: the sensation of the turbo spooling up more and generating that elastic band feeling, which is even more pronounced in a diesel based car (or old petrol, the older the better!).
Granted that modern day turbo's don't have the turbo lag of old, so the time to wait is imperceptable to most drivers and the BiTDI does a great job of masking that lag even further. Add to that, when it is accellerating hard through the gears (i.e. on boost the whole time) it is fractionally quicker than a stock TFSI, so the numbers flatter the BiTDI even further. Plus because it can generate that power at lower revs, it returns signifcantly better economy, even when driven fairly hard.... it's a phenomenal, fast, frugal car, but the numbers don't tell the full story.
In the A6, the TFSI is not a turbo, it is a supercharger so always on boost and always has near-instant response... plus it has more torque than my old V6 TDI, the only real "criticism" of that engine is that it generates the power so instantly, that you don't realise how fast it is - there's no TDI-style slingshot.
A long essay, I know... but I thought I'd save us both a bit of time and put forward both sides of the argument from 10 years ago and also present-day: the debate has evolved and people's thinking needs to evolve too.
If they were the same price and if I did well over 10k miles (the sums normally add up around 15k), the BiTDI would make sense, especially if I never wanted to get it tuned up at a later date... as a pre-reg car there was already a huge price difference and as of mid-April 2014, I've only done 5500 miles in my 12-plate TFSI... I'll take the extra potential and fun as I'm effectively driving on "free" petrol for another 6-8 years based on the extra I would have spent for a pre-reg BiTDI with the same spec.
