Custom exhaust

I plan on making a custom dual exhaust, straight back from my cat I plan on having a y-pipe and having on pipe on each side of the car. Waht pipe diameter would you recommend, should I stick with the stock 2.25 inch or a bigger 2.5 inch?

First of all you may have problems with your plan as there is very limited space under the chassis and you will have issues with a lot of things. If you want power then purchase a set of headers, go 2.5 inch pipes all the way back from a high flow cat and then to good mufflers. You will do the same thing with less hassle.