Well the TDI-tuning.co.uk mpg in middle mode experiment is over. I have tried to limit the variables as much as possible.
I ran out pretty much all the standard fuel that came with the car to empty. It then had a full tank of V-power which was ran through. Then I did a “control” fuel usage of around 183 miles and then topped up with V-power to see what standard usage was. I then ran the TDI-tuning box on for 223 miles and topped up last night, again with V-power. My actual (brim) mpg vs indicated has been all over the place for the 3 times I have filled up:-
Full tank 1 = 42.4mpg actual vs 46.5mpg indicated. Indicated = actual + 9.7%
Top up 1 (control) = 42.5mpg actual vs 44.0mpg indicated. Indicated = actual + 3.5%
Top up 2 (tuning box) = 42.3mpg actual vs 45.3mpg indicated. Indicated = actual + 7.1%
What I can say between approx. 120 miles (when the “free” fuel was used up) and 950 miles is that my actual mpg has remained pretty constant (variance either side of mean is 0.2%), even though the indicated mpg has been all over the place between 3.5% and 9.7%. This means that my car hasn’t improved at all in actual mpg, whether this is due to my driving it a little harder as the miles go on negating any gains that would be seen in driving it exactly the same way remains to be seen.
I kept my use of V-power throughout so that there weren’t any filling discrepancies e.g. different foaming characteristics causing the first click to full to come in earlier or later. Also using the same fuel throughout ensures that any gains/losses seen are attributable to the car alone and not due in any way to fuel differences causing changes to mpg. I suspect that I will achieve better mpg by switching back to normal Shell Diesel, but wanted to appraise the effects of the box on mpg thoroughly, so stuck to V-power.
My driving style is fairly sensible – I get up to whatever speed I am trying to attain quickly with moderately hard acceleration and then stay there. Once up to speed I am very economical in my driving style – I anticipate the traffic ahead well (looking well beyond the car in front – unless it is a van) and allow the car to decelerate as much as possible when needing to slow down because traffic ahead is slowing, approaching roundabouts and junctions etc. I would normally expect to get good mpg with my style of driving.
I know that once the box was on (top up 2), I was accelerating a little harder than I had been, to get up to speed, but otherwise the rest of my drive was as normal. For this I seem to have suffered no mpg penalty or any modest running in gains that I would’ve seen have been wiped out by the box.
It was nice to have that extra power on tap with the box in its middle setting (4 of 7) – supposedly the balance between power and economy. If power increase is linear between settings 1 and 7, and the boasted 243PS top output is to be believed then setting 4 should have been putting out about 213PS. I could certainly tell the difference between the box and stock power, but the power comes in linearly with the pedal – the extra power is easy to control, it’s not an “all or nothing” situation. The car seems to pull no differently than stock below 1500rpm. It seemed to me that the boxed car was at least as potent with the pedal down to just before the “kickdown” click as stock is with the accelerator pedal buried into the carpet.
After filling up last night I put the car into setting 7 of 7. The road was slightly damp and my Bridgestone tyres are sh!te in the damp. I tried to give the car a quick blast up the coast road for a junction. There is a certain road sign that I used as a marker. I accelerate off the filter lane and see what speed I can get to as I pass the sign. In my old 140TDI PD MK5 Golf this was 70mph, MK5 170TDI PD = 80mph, Scirocco 140TDI CR = 78mph and Scirocco 170TDI CR (which fully ran in felt every bit as fast as my GTD is now without box) = 83mph.
Consider that it is damp and I have Bridgestones. I accelerated quite hard (but being cautious) in 3rd. As I got a bit braver but still respecting the fact I have tyres that are sh!te in the damp, I pressed a little harder – wheelspin in 3rd at 65mph, traction control kicking in and I was nowhere near the sign. I backed right off the power and changed to 4th, passing the sign at about 80mph. I would’ve easily nailed 90 on a dry day or with better tyres.
This morning I did my daily commute and I was using a lot less accelerator pedal travel due to the extra power available. My indicated mpg for the journey was an unusually high 48.9mpg. I did a few spurts of acceleration more than I normally would’ve done. If I’d been a bit more sensible 50mpg was easily within reach. Of course I expect that the difference between actual and indicated to have opened up even further and the actual is probably still around 42.5mpg.
So I have a bit of a dilemma. A box that gives you more power on tap (a lot more power) and if used sensibly will not cost you any appreciable extra in fuel. Don’t forget though that I also have the death-trap Bridgestones. If I were to try and make the most out of the box in anything but the dry with my tyres, I would do myself (and my car) a serious injury. I have all that extra power available yet VWs poor choice of tyres for my car will see me unable to use half of it safely. Is the box really worth it for me while I still have my Bridgestones?
I consider these tyres to be unfit for purpose because even without the box on, they are atrocious in the damp. The so called “anti tramping” feature does not work with Bridgestones. Without the box, anything more than 40% throttle to pull away from a busy roundabout or junction in the damp will have you spinning on the spot and thumping the road with your front wheels. Give it more than 60% throttle doing 12-15mph in second and again you will start to spin and the traction control will be working overtime. I can’t see myself getting anywhere with VW warranty by claiming the tyres are unfit for purpose due to poor grip in the wet. It’s like they’ve taken an Olympic sprinter and given him slippers to run in! I feel aggrieved that to get my car to perform optimally and safely (without the box), I will need to shell out for at least a pair of alternative tyres on the fronts. If these tyres are sh!te on a damp road, I’m sure they will perform a lot worse as the temperature drops and the compound is even harder and less yielding in use.
