If the stock .75" MS pushing stock front and rear calipers is your baseline:
MS area = 285mm^2
Total piston area (counting the single slider is bidirectional): 10,279mm^2
We have a ratio of 36:1
So the Motorsport .875" with it’s 388mm^2 area would allow for total slave volume of 13,968mm^2 if you wanted to keep the same ratio. Looking at what’s considered acceptable travel wise people push to 39:1, which would mean ~15,000mm^2 as an upper limit.
Tricky bit is then finding a caliper set that fits within this envelope, but maintains a bias in the correct region (not want to lean on proportioning valves too much) - obviously taking into account the effect the rotor size & pad Cf.
It is a nightmare. We tend to leave all the calcs to AP, as they do it all day long. Then just work out a way of fitting everything. Even then it doesn’t always work out first time - mainly clutches in fairness. Plus some people like a pedal with a little more travel than others - you can go too far either way, rock hard pedal that’s either on or off, or spongy pedal and no brakes.
The Lotus Motorsport kit does seem to work really well as a first step, with MS master, smallish 4 pots at the front and standard fronts on the rear, with a bias valve. You will also need to adjust bias to suit wet/dry so need some headroom either way.
Bear in mind that a bias valve can only ever reduce pressure to the rear circuit, never increase it. Simplest way is to over brake the rear with pressure, then drop it with a bias valve.
I’ve just discovered the difference between the motorsport 4pot and the exige ones! The former having 38.1 x2 pistons, so work well with the front caliper out back.
I’m one for obsessing over tech details, and yes Ben precedent does could for a lot. My calcs are based on ratios from the stock setup.
Looking to use a Mazda 323 master cylinder, it’s 7/8 bore and has a fluid takeoff for the clutch. Like the motorsport one it needs holes drilling, and a new pushrod but costs £120 for a OE one.
