Hi all,

What would be the best advisable size firstly for a down pipe coming from a T25/28.
Then the rest of the exhaust?

Is 2&1/4" too small?

Thanks,
Rhys

Rhys,
A 2ltr turbo with decent power will need a 3inch exhaust, with at least a 3inch dump pipe.  This is a common size for engines like SR20DET.
In my opinion, 2.25inch is too small.  Turbo engines don't like back-pressure, so usually the bigger diameter exhaust the better (within reason).
 

For a pinto with that turbo a well built 2.5 inch dump/system will be plenty big enough, having said that if you already had a well built 2.25 inch system(mandrel bent,quality flanges and straight thru muffler) I would just run that with a 2.5 inch dump adapted to it.
Cheers

Cheers guys. Current system is not mandrel bends so I'll have to look to upgrade.
 
Thanks,
Rhys