Just looking at DTUK’s website, there are a few things there in the FAQs on their website about how gains are made that don’t ring true that some (maybe most) of the box tuners also use as a selling point:-
“Another consideration for certain vehicles is that a lower powered variant is often a restricted variant of the same manufacturers own higher powered engine. If we go back to the VAG group the 2.0 140 Common Rail and 2.0 170 Common Rail are only differentiated by the software installed by the manufacturer”.
The statement above is false – the 170TDI has different injectors and a bigger turbo. If they were the same it would be as easy to jack a 140 up to 205PS as it is to jack a 170 up to 205PS with a tuning box.
They attribute all of their “up to 15% mpg gains” down to power and torque increases which allow you to accelerate easier and stay in a higher gear. I can’t quantify it myself (they don’t quantify actual mpg gains with tests of their own either), but 15% gains on torque increases? The mpg gains are based purely on customer testimonials and not results from their own tests – most likely a growing disparity between indicated MFD mpg (based on the amount of fuel the ECU thinks the car is using) and actual mpg. I saw this with my TDI-tuning.co.uk box. Disparity between indicated and actual mpg grew from around 5% without the box, to 9% with the box in middle setting (driving in the style as I had before I put the box on), to 15% with the box in top setting. The actual mpg (brim method determination) stayed pretty much constant before and after fitment of the box.
To see appreciable mpg gains through torque increase when driving normally seems a bit pie in the sky to me, a few % possibly if you cruise at a speed that may be borderline 4th/5th or 5th/6th speed thresholds for a significant portion of your journey. To see large available power increases with minimum fuelling penalties (when not hoofing it all the time) seems a far more honest claim. I seriously doubt these boxes will pay for themselves in fuel savings based on my recent experiences.
I was chasing higher mpg with my box because my standard output and mpg is disappointingly low (possibly down to the use of V-power Diesel which is less dense than regular and has a lower Cetane value), I don’t think it’s really a viable reason for having the box. Extra power, noticeably so and smooth in its delivery – the TDI-tuning.co.uk box I got really delivered on performance.
Buy a box for the power and not for the mpg and you won’t be disappointed.
