Does switching to bigger exhaust valves kill velocity?

Just a questions for people who know stuff about heads...Does switching to a bigger exhaust valve kill velocity in any way? or is that with a bigger intake valve that velocity might be a problem. How does switching to bigger valves on an unported head influence the changes over stock? I have a set of GT-40X heads and the intake valve is 1.94 and the exhaust is 1.54...Just curious if I would run into any porblems if I switched the exhaust valve to a 1.60 on an out of the box head. Please let me know.

BTW: I would use something along the lines of an E-cam or some other emmision legal cam for the heads.

-Greg

So you can't just put bigger exhaust valves without porting...right? How reliable would that make the car assuming everything else is emmision legal? Thanks for the info.