What sort of mods would you need to do to get a 1ggte upwards of 250rwhp?
Um you would be looking at needing to change injectors, for bigger items, make sure your fuel pumps are up to the task, some sort of after market engine management, bigger and better than stock intercooler, and you should be looking at using bigger turbos or go a conversion to a single turbo (i have yet to see a 1ggte with standard twins run that sort of power)
Would this still be useable as a daily driver with this sort of motor?
You would be able to drive it daily, but it would prob be a case of dont put your foot down in the wet, and you prob wont be using at as a daily when the local law enforcers find out about it. I was using my single turboed 1g 23 as a daily until it cost me 6 points of my licence in 2 weeks. Also depends if you like a car the would prob leak like a sive when it rains also.
How much power increase should I expect going from a carbied 18rg to a 1ggte?
Um it will feel like a different car to drive.