HH56 wrote:
That appears to be the Electroboost system and a few have been installed on 55-6 models at the factory location and 1:1 ratio with the boost power set near maximum. I believe those master cylinders were all 1". If you go that route on a 53 you would need to convert to 12v and I cannot help but wonder with the low ratio about how well the brakes work if the boost unit failed. To the best of my knowledge no one using the 1:1 ratio has tried disconnecting power to simulate a failure or if they have, did not post the result.

I and several others would much like to see what would happen with a 3/4" or smaller cylinder at the 1:1 ratio. I don't remember the exact ram size in the BTV but think it is around 5/8". It can have a longer almost 4" stroke to displace or force fluid out of the cylinder in sufficient volume to fill the cylinders whereas a modern master cylinder has a comparatively short stroke large diameter piston and quickly pushes a fair amount of fluid ahead of the piston. If the brake shoes are adjusted properly not much volume is needed but discs and poor adjustment would need more. That is where the safety margin question of how much stroke for the reduced diameter cylinder is available to move the equivalent amount of fluid. Most modern boosters and cylinders seem to have a max stroke no more than about 1 1/2 - 2 inches