its mainly cost cutting, reliability and emissions.
we dont face many problems with the box installed because the tuning is still within the car's tolerance levels. the manufacturer are not willing to take it that far.
there is a nice discussion on hellstar's thread about his pete'd verna.
the injection timings and sequence is changed.
as far as I understood, the injector that deals with torque production is given extra duty, and the pilot injectors which smooth out combustion are used to compensate. this is just what i understood from the explanation sameel gave on that thread.
i also suspect, the box makes the turbo work harder to supply more air.
smoking is a problem under hard acceleration, but should disappear with better air supply(cold air intake)
fuel efficiency showed a marginal increase in my initial runs(by 0.8kms per litre) I attributed this to higher torque being available at lower rpms. but buying the box for fuel efficiency is silly. the temptation to floor it on every open stretch just to feel the roll on acceleration is very strong. you will end up revving the engine like a petrol.
my poor swifts tacho now regularly sees numbers like 4000rpm. highest I went before the box was 2900
more torque, and speed means greater stress on all components , true, but its well within the tolerance limits of the car. we can afford to take that risk. manufacturers who produce cars for the average joe public cant afford to do that.
here's the link
http://www.team-bhp.com/forum/long-t...x-added-6.html (Hyundai Verna CRDI VGT - Updated at 22k-km, 35k-km & 40k-km, Plus A Minor Crash)
if you follow the discussion to the end, you'll see what I mean.