Timing constrains wont affect path

Hi everybody,

Im working on my first "big" vhdl project using quartus II 12.1 and 
Cyclone IV E device.

my problem is that im trying to improve paths timings all over my design 
but timing constrains have no affect over the paths im trying to 
improve.

i started with the long paths and reduced it down to 2 basic blocks and 
nothing.

i know my describe is very general but i feel like im missing something 
very basic and simple.

found nothing online about this kind of problem and altera's timing 
guide was no help either.

to be more specific if it helps, my design is asynchronous (so no clock)
and im currently trying to use set_max_delay constrain to improve 
routing efficiency.