what would the difference be if i went to a 3 inch fwi from a 4 inch fwi i have a 4 in metal dryer vent tube from tb to fender well and it looks well..... unprofessional .i found a 4 in to 3 in rubber reducer for my tb end and i was going to make it 3 in all the way to fenderwell with smoothe pipe less turbulance but will it affect my performance going to a smaller diameter pipe.

spectre has a 3.75 build your own intake kit that u can get a autozone it works pretty well i have oone on mine

You can also go to Intense racing or ZZ performance and order a flex tube in what ever size you need.

what are the pros and cons of 3 inch vs 4 inch or
is one inch difference not really that big of a deal

Bigger is better on intake. Will it make any real difference, not very much.