How low?
 

i Have the adjustment bolts on the rear spring plates in my 911, how low will adjusting this drop the car? Or do i have to take the torsion bars caps off. My car is 77 911.

You can usually get about an inch of adjustment fromt he eccentrics. If you can't get it low enough with those, you will need to re-index the torsion bars. Please read about this procedure before starting to tear your suspension apart. Use the search feature and you will find more info than I could write in this little box. It's not a hard task but can be intimidating.