Re: BTV blues...

Posted by HH56 On 2010/6/17 8:18:18

Believe you hit upon the reason BTV can get away with 1:1. It does not have a piston in the conventional sense. Actual dimensions are on the forum somewhere, but the "cylinder" is a chamber filled with fluid around an inch in diameter. One end has the "piston" which is a rod around 3/4" diameter but does not touch the cylinder walls. As soon as the pedal is moved, the compensator valve closes trapping the fluid. The only place fluid can go is to the wheels when the rod is pressed further in to displace it. How far pedal moves depends on wheel cylinder/shoe adjustment, but since it is a narrow rod with a long travel, that provides the advantage and volume.

Conventional masters have all the fluid pushed ahead of the piston and since there is a greater surface diameter, more volume with a shorter stroke is obtained at the expense of mechanical advantage due to that same large surface area having to push all the fluid instead of just displace or squeeze it out. Hence the need for a higher mechanical advantage at the pedal to achieve the output pressure.

The 7" booster is larger than the BTV and will provide more assist, all other factors equal. Those with math skills can work out the actual boost but the disadvantage again comes due to the short travel and large piston vs small piston and long travel in the BTV.

There are other products similar to the inline boost you mention but again, they just provide a slight addition to what is there to start with.