Car: 1991 CRX Si
Brakes (stock): 4 wheel discs, 9.5"/9.2" (f/r)
Brakes (now): fastbrakes 11" 4-pot / stock (f/r)

now i know lots of crx's dont come with rear discs (since only the Si's did) and the rear disc swap from another CRX or integra is a popular swap. seems also that the popular consensus is that a 40/40 prop valve is essential in the process.

my question is why? the stock crx si, which has rear discs stock, does not have a 40/40 valve. i believe mine is a 40/20. so why does everyone recommend the 40/40 over what comes with the crx si stock?

does anyone have any evidence to what these number ACTUALLY represent? and in my case specifically, would moving from a 40/20 to the 40/40 really do anything? and if so, what?

im sorry if this has been covered in detail before, but i tried to search but could only come up with thread upon thread of fs/wtb for this valve, or people saying how you need the 40/40 for rear discs.

 

IIRC it's just a part number; "4040" or "4020". Saying 40/40 or 40/20 makes it seem like it represents the forward/rear bias.

There was a thread on HS where some people tore down some prop. valves(including myself), though no one really looked into it much(speculated may have to do with orifice size and/or spring; I believe there was different color springs in the prop. valves that were opened).

 

if you have a custom brake setup and have altered the weight distribution of the car, then using a 4040 isn't really really advantageous, should really be using a custom adjustable proportioning valve to get the most out of the brake system

 

The 4040 should give a more balanced feel, the 4020 is designed for the small drum brake, the split points for the pressure front to rear is different. You can always use more aggressive rear pads to change balance.

 

you have a 40/20 before because you have a smaller rotor.. and doesn't need to much pressure.. and i think your engine is B16 dohc it has more power in the front that's why you have 40/20 prop valve..

in some stock cars it has 30/30 prop valve because it has a sohc engine with small front rotors and small rear drum brakes..

now when you upgrade your rotors and calipers.. you need to upgrade your prop valve to 40/40 and master/hydrovac to 1' or 15/16

so you can feel and maximize the performance of your brakes..

 

I will confirm the differnt color spring in the valves as i was to wanting to know having converted drum to disc in the rear and then wagon V6 front brakes on my accord.I upgraded the booster and the master to the wagon stuff considerably biger i might add and found the 40/40 works the best. I found the valve out of a DA integra and swaped the bracket.