NEW Group Buy 914 Master Cylinders $110 each, GB CLOSES TODAY 11/15/17 The rest will ship by 11/2 Options

[Mikey914]

I'm working on having new master cylinders made for the 914's. They are going to be 19mm to crossover for the 911 also. Now you can get a quality part at a reasonable price. These are about 90 days out, but they will be a quality product, that is fully engineered.

Who's in?

[Dave_Darling]

When you install a larger master cylinder, you reduce your "hydraulic advantage" over the caliper pistons. It's almost exactly the same effect as moving the pivot point of the brake pedal.

The 19mm M/C has 25% more area to the piston than the 17mm one does. That means to get the same clamping force at the calipers, you have to exert 25% harder, though the pedal moves 25% less distance.

Most people seem to agree that the 19mm is a reasonable swap, but going up to 23mm (which I believe the earlier thread was talking about) is a Very Bad Idea unless you are significantly upgrading the caliper piston sizes.

--DD

[TC 914-8]

When you install a larger master cylinder, you reduce your "hydraulic advantage" over the caliper pistons. It's almost exactly the same effect as moving the pivot point of the brake pedal.

The 19mm M/C has 25% more area to the piston than the 17mm one does. That means to get the same clamping force at the calipers, you have to exert 25% harder, though the pedal moves 25% less distance.

Most people seem to agree that the 19mm is a reasonable swap, but going up to 23mm (which I believe the earlier thread was talking about) is a Very Bad Idea unless you are significantly upgrading the caliper piston sizes.

--DD

Dave,
My car has the Brembo Boxster calipers up front, not sure if the MC was ever changed. My petal is still soft after many bleedings and purgings. You think a 19mm is a good choice? Or 23mm that came w boxters?
I have stocks w V kit in rear
Just curious

T

[Dave_Darling]

My car has the Brembo Boxster calipers up front, not sure if the MC was ever changed. My petal is still soft after many bleedings and purgings. You think a 19mm is a good choice? Or 23mm that came w boxters?

The Boxster MC will be boosted. Without a power assist, you may find that the 32mm one requires a large amount of leg to activate.

I don't know what the piston sizes in the Boxster calipers are like compared with the stock ones. It's good to keep near the stock ratio of total caliper piston area to master cylinder piston area, but I don't know the specific numbers for your case. But that should keep the pedal effort near stock.

--DD