I have a RST S2 engine running about 250bhp but now I’m looking for some monster power. I’m not sure whether to make a 2.1 ZVH conversion or a full 2.1 Zetec turbo. Once in full race trim, will there be any big difference in power between the two? And what about the money that I will need to spend on each? Which of the two options requires the most modifications in the head, bottom end, etc.?