Maintaining a reasonable brake balance with calipers from a different car.

[d3c0y]

So i have assembled 60% of the brake kit for my car.

It currently consists of:

• Porsche 986 Boxster calipers front and rear (986 Boxster weight is 1280kg)
  
• RX-8 Sport 320mm x 24mm DBA 2 piece rotors drilled for 4 x 100 PCD
  

Caliper piston sizes:

• F Disc 298mm, Pistons in Calipers 2x40,2x36 mm , pad area 216 cm^2
  
• R Disc 292mm, Pistons in Calipers 2x30,2x28 mm , pad area 196 cm^2
  

 

 

Stock Boxster rotor sizes:

• 
   
   
  
• Boxster front - 298mm x 24mm - 6.67kg
  
• Boxster rear - 292mm x 20mm
  
• 
  

Ok so my questions are one, will going up to a 320mm rotor in the front overcome the what I am assuming would be a more rearward bias this car would have from the factory being rear engined?

 

 

Two, is there any point switching to a manual brake master cylinder to save weight and get more pedal feel? I have read that engines with big cams don't work well with boosters as the vacuum isn't there to power it so you are better off with a properly setup up manual system.

 

 

Just to put in, that i don't want to go to the expense of an aftermarket pedal box at this point, but will obviously get a proportioning valve to help setup the bias correctly. Also how much difference can you get with the proportioning valve?

[dat2kman]

Make this less painfull!

What is square mm of total pistons in each front caliper?

PieRsquared?

What is rear sq mm

 

What is sq mm size of master intended?

 

The volume of fluid displaced ( required by the four calipers) will dictate the madter size.

Your master size is now the variable!

Also slightly variable is pedal leverage ratio, ( but not much!)

 

The leverage factor for brake rotor, relative to wheel total diameter is a minor consideration, not important though.

[dat2kman]

And,

Yes,

The fitted to rear line, Pressure Reducing Valve,

Will work admirably, as your rear pad sq mm sizing is too large for the wright bias of the propsed car, compared to donor car.

Other option, is to machine off a % of the rear pad material.

 

Dont get hung up on rotor sizes, stick on what fits, with, whatever the smallest rim size you may end up using, on the car.

[d3c0y]

Well the master cylinder size in a boosted situation is 15/16ths as that's what the Porsche runs.

 

 

Front calipers are 45.49cm^2 each, rears are 26.45cm^2 each.

 

 

 

15/16th mc = 2.38cm diameter = area of 4.45cm^2

 

 

So how do we now relate these figures?

 

 

 

Removing area off the rear pad, as far as I'm aware doesn't reduce clamping pressure, just its heat dispersal ability so i don't see how reducing the pad size will effect the bias?

 

 

From your last statement i want the smallest rotor i can run with the calipers to save on unsprung weight right?