depends what you want from the car, td05 will give higher figures but you will get more turbo lag. a td04 suits most people as you can be running 250hp but with the td05 you could be up to 350hp etc. what will you be doing with the car? if you are aonly using it on the road i would say td04 will be plenty but if you plan on doing alot of drag racing then td05 will get you better times as long as you have a gd set up. before you go bigger power though, have you got a good suspension set up and decent brakes? better to do that before you go big power, nothing worse than going fast in a straight line but cant stop or go round corners
