When it comes to boosters bigger is always better, but sometimes we just can't fit the bigger boosters in there. So if you're running a small block with stock valve covers then you can run the factory style 11" booster. If your running tall valve covers or an LS1 then you would want to run an 8" dual diaphragm booster so you have enough clearance between the valve cover and booster.

The smaller the booster the less power it will put out. For example a 7" booster will hold enough vaccumn for 1-2 good brake pedal hit. After that it will like manual brakes until it gets a chance to build up more vacuum. With 8, 9 or 11 boosters you won't have this issue becuase the booster is able to store more vacuum.

If you are going to drill the cotter pin hole than use your spindle to help mark the spot. Tighten the nut to 15lb. feet of torque and back it off one flat and drill your hole. If you don't choose to do this i can sell you a spindle for 99.00.