[s-cars] [urq] S-Car Brake system conversion- Read- no more PSpumpintegration <question>

[John Cody Forbes]

> Cody Forbes wrote:
>> Another route is to delete the assist, leave the stock master
>> cylinder, and increase the size of the brakes. Larger brake pistons
>> have the same effect as smaller master cylinder pistons - travel
>> increases slightly, but so does leverage. Perfect excuse for going
>> for some big reds!
> 
> I'm a little late on this one, but I just wanted to point out that
> bigger brakes don't necessarily equal bigger pistons.  The effective
> piston diameter of a G60 is (surprise!) 60 mm.  All of the 4-pot
> Porsche calipers I looked at a couple of years ago (including big
> reds and 996tt) were less than that.  Of course, you're still getting
> a leverage boost with the larger rotor diameter.     

Actually I think you may be mistaken. A 996TT caliper has 4 pistons, 2 36mm and 2 44mm. That would give a total piston surface area of 3553mm^2. A G60 has one 60mm piston. A G60 would then have a total piston surface area of 2826mm^2 - roughly 25% less than the Porsche part. If you factor in however much the pistons move (1mm each maybe?) you can see that the used displacement in the Porsche caliper is indeed more. I can't find the info for a Boxster caliper, but if anybody knows the piston sizes you could think back to geometry class (I had to google it ) and use pi times radius^2 for each piston then add the 4 areas together for total piston area.

-Cody Forbes