I have a nikon d3100 and i shoot in RAW so how many images can i hold on a 8gb sd card?

The camera is 14 mp

There are NO LESS than two ways of finding out.
1.look in your Owner's Manual… There's a chart in it that shows you how many images you will be able to shoot.
2.read the information on your LCD screen. It's not difficult. Your Manual will show you how to read all the information that's displayed on your screen.

I have a Nikon D80 and I can get 630 images in the RAW format with a 8gb sd card.

Or just do the math. Look at the properties on one of your raw files… Find the size in mb and divide that into the size of your card and wala, you've got a rough idea.