having alot of trouble with screen width and projector distance what is the largest screen size and how do i get there

Not sure what you mean, but HD8 lenses are good for 1,4 - 6,0 m wide picture.

But 808s light output is going to be problem after 2.5-3.5 m wide picture, resulting dim picture. For 3 m wide (118 inch) 16:9 picture projector need to be about 4,1 m (161 inch) from the screen.

You can calculate rough projection distances using
1.4 * screen width = projection distance

Or you can download Barco Lens Program.
http://www.barco.com/events/en/downloads/lensProgram.asp

The largest possible or the largest with a good image?

That largest with a good image is about 8' wide and preferably about 1.3 gain.

Calculators put the machine a little to far back, so the best way to do it is set it up on the floor, measure, then put it on the ceiling.

If you want to see what barco says download the Barco LENS program from here:
http://www.curtpalme.com/Barco808_Downloads.shtm

Generally for an optomized set up, you end up about 5-7% closer than what it says.

If you want the best picture, follow these instructions:
http://www.curtpalme.com/Focus_and_Mechanical_Aim1.shtm

Dave