I have 98 hatch with a B18c with 2.75 inch exhaust and i want to put a resonator on it. But, the resonator I have laying in the shop is a 2.5 inch, so my question is will I able to feel a power loss if I use it?

 

prop you cant feel it but it will be there.
the bottleneck effect !

 

Buy one that matches the pipe.

 

You won't feel any difference

 

Would you care to elaborate?

 

Stick to that test pipe, just because it's bigger doesn't necessarily mean more power.Check my build thread I did 243 with a WS2 Exhaust, the piping on that isn't even 2.5.

If you have money buy another one if not then just use the one you have, you wont feel the difference. Put the money towards something else.