I plan on switching the stock dual master cylinder on the TR8 out to one of those Tilton or Wilwood setups with the dual masters and balance bar. I'm a little confused about sizing. If on the stock one, the pedal is pushing both at once, and the master is 13/16, does that equate to doing two separate masters that are both 13/16? Or, is there something inside the master that makes the front 13/16 and the rear smaller? I'm not talking about the external proportioning valve. I know that diminishes the volume going to the rears. My guess is the force is one and the same both front and rear when it leaves the master, but the prop valve drops it to the rears making it in essence smaller???? So starting with a 13/16 front master and a 3/4 rear is a good start? That is assuming the calipers will remain the same. But they won't.... I'm going Wilwood all around, so I am probably going to need a brake line pressure calculator of some sort. For some reason I see a box of spare masters in my future.
Contact Willwood, since that is the hardware direction, and see if they can help you out. They had a speaker at the motorsports conference back in February, that was very helpful and willing to make sure the customer (you in this case) got what you need the first time out.
The size of the master on a dual circuit cylinder can have two bore sizes by using a stepped bore and piston setup. If you have the stock piece out and don't mind tearing into it, you could check for that.
The size calculator you mention is a basic master piston area vs caliper piston area (for a single side if pistons on both sides) comparison. (Input force * master piston area)/caliper piston area = Output force (clamping force). The Wilwood tech you speak to should be able to help you out with that too.
In reply to tr8todd:
Ask and you shall receive. My buddy Todd has a great tool for this:
http://www.tceperformanceproducts.com/dual-bias-calc/
This is how I chose the dual masters for my own Wilwood setup.
If you need MU info this is a good chart
