I am curious as to what Hyundai does to put out 300HP from their 1.6L turbo WRC i20. But I imagine that this is all a secret... for now. I'm not saying that I want 300HP but 250HP would be sweet.
My guess would be that from an engine perspective it's going to have seriously uprated internals, likely a different compression ratio too. Intake and exhaust will have been fine-tuned, and possibly a different turbo too. Not sure what fuel they use, probably 100 RON though, and then to top it off, the ECU will have been mapped for the setup, and of course for the performance, with a bit of reliability thrown in, unlike our map, which I have a feeling is very, very conservative.
In addition, where does the 300BHP figure come from, by that I mean, is that from the engine itself on a dyno, or from the car running on a dyno. If it's just the engine, then it'll be less when in the car. If it's when in the car, then also factor in the weight of the WRC car, which will be less than a road car.