Has anyone used a t4 to t6 adapter on their current hot side piping ? Have you noticed any problems or regrets of not just redoing the hot side.

 

I used one, if your hotside is already proper size then the biggest restriction is still the turbine. Plenty of people run stock manifolds and 2" pipes to either turbo flange with good results.

One I used was like this, as you can see its not a huge difference and its contoured to flow well:

 

I have 2" running into 2 1/2" now. Was curious if that had to be redone to adapt to make it work well. Thanks

 

You'll be fine with that setup.