Its probably just that! A chip that turns up the fuelling and timing and a high-lift cam that enables full utilization of the added fuel. In terms of BHP these engines (1kd and 1hd) will still be making less than petrol ones, but they probably are getting tremendous amounts of torque quite early and fairly constant through the rev range. In our little dyno experiment of turning up fuel and timing on the 2LT while the BHP gains were marginal, we were calculating (not sure how accurately) some 200 ft.lbs of peak torque on something that is supposed to net about 140. So with the 1KD at 260 ft.lbs once you turn up the fuelling, timing and boost, they are probably getting 320+ ft.lbs from 1800 to 3500 rpms. Thats a whole lot of torque and with the drivers getting better and better at putting it to the ground, no wonder that the Vigos seem to be getting faster every season.