Earthing is a big prob when you start getting up in the higher horsepower there's alot of aftermarket kits for most big horsepower cars. I don't know if you remember but my car 's arlam used to come on while driving(eg the car would shut down at any speed) that was due to poor earthing perfect for a std car but when modded it caused problems. What I think you will find trev is your car like mine is not built to back bullsh*t high horsepower. Yes the car will make good power and the engine will handle it to a safe point but the whole car was designed to handle 190wkw not 300wkw it will take a little time to iron out little problems stick with it. I took my wrx from 94wkw to just over 220wkw and it took me over 6 months just to get all the little problems sorted with it . Building a fast car can take a week building a fast reliable car takes some time.