I wanna know all about the tuning and what it does?
what's open filter is and what it does.. how is a new exhust is helping? and everything you can tune not just that
and what is the top speed tuning can give the engine?
sorry about my english it's pretty bad i know

 

the question isn't as easy as twist this and turn that. scooby may get on here and write a book, he knows a lot. if your ds is stock it is probably tuned well. if you change a pipe that will change how the exhaust gas leaves the machine, which you would hope was easier with a 400 + dollar pipe, which makes it easier to get more fuel into the combustion chamber, but at the same time it probably will change your air fuel mixture requirements, and if not done right could cause you to be slower than before. if you run what you had you will most likely be on the lean side which will cause your machine to run hot. well there is a lot more to this than what i have put down so a book might help you a lot.