help choosing master cylinder size

[SHEPPO3930]

Hi all,

I am at the point of my car's rebuild where i need to sort out the new brake package. I have purchased all the brake hardware apart from the master cylinder itself as this needs some expertise regarding choosing the right diameter.

My set up is as follows:

Car: TA22 Celica w/ 200kw 4agte for club sprints & hill climbs, general track days, etc.
Front brakes: ~290mm rotors, FD RX7 4 pot calipers, CNC adaptors on XT130 struts
Rear brakes: Volvo diff with standard ~280mm rotors & 2 piston calipers
Other stuff: Wilwood bias valve on rear brake line, no brake booster, 15" rims w/ 205 semi slicks.

Since the car had a totally different brake package from when it was last on the track, I have no idea where to start regarding master cylinder size. Can anyone help?

Thanks,
Dave

[bmxer54]

Not sure if this will help as i'm sure the piston sizes between the calipers will be different, on my corona i have r33gtst calipers all around, a brake booster and a 15/16 master cylinder
the booster is only really there to soften up the pedal really isn't it? I had a 1 inch master cylinder in there before but it was a bit firm with not much pedal feel so i went down a size
since you have no booster then surely it doesn't matter what the master cylinder bolt spacing is, Why don't you first try an FD RX7 master cylinder and work from there?

[Javal]

Was your car running an boosterless setup before? If so, what i'd do is work out the total surface area of all of the pistons (F+R) vs the surface area of the master cylinder piston on your previous setup. That'll give you a ratio of slave surface area vs master surface area

Then work out the total surface area of your current setup and size use the same ratio to calculate your desired master cylinder size.

If you were running a booster before, well, have fun.

[SHEPPO3930]

yeah if the car had any common components from it's pervious life it would be easy.

It was running a standard ta22 master w/ booster, with early commonwhore single piston girling calipers and tiny 260mm'ish magna discs and stock drum brakes at the rear. it also had 88rwkw, no suspension and was basically relying on a loose driver to pull off the lap times (hi Andrew!).

I noticed takai was running a Datsun master cylinder when he had fd calipers and no booster so i'm probably going to start with that and report back my findings.