if i fit a s3 front pipe instead of the standard pipe what can expect to happen to how the bike runs ? i mean is it worth the change   thanks 

You can expect to burn yourself every time you fall on it. For some reason the titanium pipes are always hotter. In my experiance the difference is minimal. You get much more benefit from buying a set of jets and taking the time to properly tune the bike. In general the length of the header pipe determines the tuning. Long header pipes are better for low end power as they have resonances tuned for lower RPM.   The shorter pipes are great for the high RPM expert leaps but difficult to control for the average plonker. The pipe material really has no effect on the engine behavior. The pipe could be made of cheese and would work the same as long as it held its shape.

Unless you're pushing your bike to the limit the main effect is probably psychological (and financial). Not to mention the spirit-crushing post-crash realization you just dented your $400 titanium pipe. Been there, done that, only it was an Akropovik.

if you want one and can afford it go for it. But it won't make as big a difference in useful performance as a set of carbon fiber reeds.