A4 Avant V6 TDI - Modification cost estimates?

A4 Avant V6 TDI - Modification cost estimates?

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LotsOfLaughs

Original Poster:

188 posts

15 months

Wednesday 20th March
quotequote all
So Ive got a petrol Subaru Legacy R Spec.B with a 3.0 petrol flat 6. I like almost everything about it, but it drinks fuel (20-25mpg over a tank, depending on driving style etc) and Ive done a few mods and now its at the limit of how much power it'll make without spending thousands on a completely custom turbocharger setup.
So, Im thinking of getting a diesel. Unfortunately, Subaru only ever made one diesel engine, a 2.0 boxer 4, and it was utterly terrible. Thus, Im left looking at Audis. The A6 is definately too big, so its the A4 Avant Id want. Now, which engine? Thats simple really, the RS4 is too expensive, the S4 will drink even more fuel than my current Subaru, and is barely any quicker (yes its got more power, but its also 300kg heavier). The 4 cylinder engines did cross my mind, the famous PD-engines, but they dont really make enough power without spending lots of money on internals etc, and the 1.8T and 2.0T as found in the Golf GTI (I think?), but once these are tuned to the power my Subaru makes, they wont use much less fuel anyway, so whats the point?
That leaves me with just one engine left, the 3.0 TDI V6. Itll make the same power as my Subaru from nothing but a remap, and use half the fuel, or at least that's what Im led to believe. How far can it be pushed without spending silly money (i.e. just the usual bolt-ons, downpipes, turbos, intercoolers, injectors, etc?) and how much would those bolt-ons cost?
I know this is a VAG forum, so do forgive me for mentioning the B-word, but how does the 3.0 V6 diesel A4 compare to say the BMW E91 330d, in terms of performance, fun, and cost to make "Jesus thats quick!" power?
Thanks!

Lotobear

6,349 posts

128 months

Wednesday 20th March
quotequote all
LotsOfLaughs said:
So Ive got a petrol Subaru Legacy R Spec.B with a 3.0 petrol flat 6. I like almost everything about it, but it drinks fuel (20-25mpg over a tank, depending on driving style etc) and Ive done a few mods and now its at the limit of how much power it'll make without spending thousands on a completely custom turbocharger setup.
So, Im thinking of getting a diesel. Unfortunately, Subaru only ever made one diesel engine, a 2.0 boxer 4, and it was utterly terrible. Thus, Im left looking at Audis. The A6 is definately too big, so its the A4 Avant Id want. Now, which engine? Thats simple really, the RS4 is too expensive, the S4 will drink even more fuel than my current Subaru, and is barely any quicker (yes its got more power, but its also 300kg heavier). The 4 cylinder engines did cross my mind, the famous PD-engines, but they dont really make enough power without spending lots of money on internals etc, and the 1.8T and 2.0T as found in the Golf GTI (I think?), but once these are tuned to the power my Subaru makes, they wont use much less fuel anyway, so whats the point?
That leaves me with just one engine left, the 3.0 TDI V6. Itll make the same power as my Subaru from nothing but a remap, and use half the fuel, or at least that's what Im led to believe. How far can it be pushed without spending silly money (i.e. just the usual bolt-ons, downpipes, turbos, intercoolers, injectors, etc?) and how much would those bolt-ons cost?
I know this is a VAG forum, so do forgive me for mentioning the B-word, but how does the 3.0 V6 diesel A4 compare to say the BMW E91 330d, in terms of performance, fun, and cost to make "Jesus thats quick!" power?
Thanks!
In the real world you will feel the 3.0 Audi TDI is quicker than your Spec B even in std form - the torque (its trump card) is amazing and will massivley trump a Spec B

The A6 is not that much bigger than an A4 Avant and with air suspension it is a vastly superior car IMHO

I've had a series of Legacys - great cars but my current A6 Allroad C7 is better in almost every way (I came off an A4 Allroad).

If you fancy something really quick get the Bi Turbo diesel but for me the 245bhp diesel is just fine, with serious shove when you need it and 44mpg on a run or 36 day to day

Dr G

15,177 posts

242 months

Wednesday 20th March
quotequote all
The twin-turbo lump in A6/7/SQ5 uses a stronger gearbox if chasing numbers is your aim.

An SQ5 is also the same size (footprint) as an A4 if a larger car isn't what you want.

LotsOfLaughs

Original Poster:

188 posts

15 months

Thursday 21st March
quotequote all
Lotobear said:
In the real world you will feel the 3.0 Audi TDI is quicker than your Spec B even in std form - the torque (its trump card) is amazing and will massivley trump a Spec B

The A6 is not that much bigger than an A4 Avant and with air suspension it is a vastly superior car IMHO

I've had a series of Legacys - great cars but my current A6 Allroad C7 is better in almost every way (I came off an A4 Allroad).

If you fancy something really quick get the Bi Turbo diesel but for me the 245bhp diesel is just fine, with serious shove when you need it and 44mpg on a run or 36 day to day
Ahh, the old petrol vs diesel, torque vs power debate. The truth is, it really depends how you drive, and if you can be bothered changing gear. if your crusing along the motorway in 6th gear at motorway speeds and mash the accelerator, yes, the diesel will pull away. If you put them both in the correct gear for the speed, the petrol will pull away. I did the calculation a while back (different cars) and its not that hard, all you need is the dyno graphs and final drive gear ratios and the tyre size, and the weight of the car, and if you want to get nerdy and specific, the drag coefficient.
The switch to diesel for me isnt about that really, although it is appealing, Im quite happy to change gear too.
The A6 is too big for me, and its very very heavy, according to a quick google, the V6 tdi manual is over 1800kg, thats 300kg heavier than the Legacy, 20%... so it would need an extra 50hp just to keep up, in theory.
I thought all the Bi-turbo V6s were autos? And circa 40mpg is the whole point of it for me, that and more pace...

LotsOfLaughs

Original Poster:

188 posts

15 months

Thursday 21st March
quotequote all
Dr G said:
The twin-turbo lump in A6/7/SQ5 uses a stronger gearbox if chasing numbers is your aim.

An SQ5 is also the same size (footprint) as an A4 if a larger car isn't what you want.
Thanks, Im after a manual though. And SUV/crossover/soft roaders really arent my thing.

Lotobear

6,349 posts

128 months

Friday 22nd March
quotequote all
LotsOfLaughs said:
Lotobear said:
In the real world you will feel the 3.0 Audi TDI is quicker than your Spec B even in std form - the torque (its trump card) is amazing and will massivley trump a Spec B

The A6 is not that much bigger than an A4 Avant and with air suspension it is a vastly superior car IMHO

I've had a series of Legacys - great cars but my current A6 Allroad C7 is better in almost every way (I came off an A4 Allroad).

If you fancy something really quick get the Bi Turbo diesel but for me the 245bhp diesel is just fine, with serious shove when you need it and 44mpg on a run or 36 day to day
Ahh, the old petrol vs diesel, torque vs power debate. The truth is, it really depends how you drive, and if you can be bothered changing gear. if your crusing along the motorway in 6th gear at motorway speeds and mash the accelerator, yes, the diesel will pull away. If you put them both in the correct gear for the speed, the petrol will pull away. I did the calculation a while back (different cars) and its not that hard, all you need is the dyno graphs and final drive gear ratios and the tyre size, and the weight of the car, and if you want to get nerdy and specific, the drag coefficient.
The switch to diesel for me isnt about that really, although it is appealing, Im quite happy to change gear too.
The A6 is too big for me, and its very very heavy, according to a quick google, the V6 tdi manual is over 1800kg, thats 300kg heavier than the Legacy, 20%... so it would need an extra 50hp just to keep up, in theory.
I thought all the Bi-turbo V6s were autos? And circa 40mpg is the whole point of it for me, that and more pace...
User name checks out

LotsOfLaughs

Original Poster:

188 posts

15 months

Friday 22nd March
quotequote all
Lotobear said:
User name checks out
Newtons 2nd law of motion, F = M.a.
Multiply by distance, force x distance = work, thus, W = M.a.d
Divide by time, work/time = power, thus P = M.a.d/t, and d/t is speed, or velocity P=M.a.v
And so, clear as day, you can see that if you have a constant mass and a constant initial speed, acceleration is proportional to power, not torque.
(Note, this applies at any single moment in time, so you can calculate the instant power of your car if you know its mass and speed exactly, this is how those dyno apps on your phone work)
The alternative explanation to this is that cars accelerate when they have the most torque AT THE WHEELS, and since every single engine makes peak power (engine) at higher rpm than peak torque (engine), you need a lower gear for peak power (engine) than peak torque (engine) at the same speed.