[mnm99]

Long story short I am trying to get my brakes to work again. Old setup was a 11" booster with 1 1/8 master and large piston calipers. That setup worked ok,but I need a smaller booster (bigger engine) and want to get this to work. After installing the 8" duel Dia booster the brakes got very hard and could not stop. Here's my question. I have 12" of vac at idle. I bought a canister but didn't hook it up yet.

If I went with a 1" bore master and relocated the brake pushrod like a manual brake setup ( top hole ) by getting a different bracket to to mount the booster and added the canister do you think that would do it? Could I go to a 15/16th bore and still have pedal left?

I know about vac pumps and hydroboost. I wanted to see if I can get this to work first.

[davidpozzi]

If you used the top hole and a 15/16" bore master cyl with pushrod in the upper hole, you wouldn't need a booster at all. That might be a good option.

Just by switching pedal holes, you are doubling the pedal ratio.
Power is 3.8 to 1, Manual is 6.25 to 1.

A drop from a 1 1/8" bore to 1" bore would give you aprox 1/3rd more power alone.

On the bore size:
Bore ......Area sq in
1 1/8"   .994 
1"         .785"
15/16"   .693"
7/8"      ..601"

[mnm99]

I ended up just shimming the booster for now so it lined up with the top hole. What a difference! I do have alot of travel now though. How high should the pedal be off the floor for manual brakes? I had to remove the brake switch stopper for the rod. I ended up adjusting the brake switch back down 3/4.