4 wheel disk and adjustable proportioning valve question

[turbobitt]

I have Aerospace brakes pro-street brakes front and rear on my car. I converted over to manual at the same time and in process of working out the brake pedal geometry and master cylinder size to get me the brake feel I'm looking for. So far I have the 1 1/8 master and the pedal is set up to an exact 7:1 ratio. The pedal feel is tolerable but could be better and plan on switching over to a 1 1/32 bore cylinder.

The master cylinder is plumbed per the instructions with the rear port going to the rear, and front port going towards the front brakes for drag race applications.

If I hit the brakes hard it will lock the rear brakes. I been debating on putting an adjustable valve in-line to the rear brakes. Now maybe I'm overcomplicating this and looking to deep into the set-up but knowing how the master cylinder operates seems to conflict with some of logic of using an adjustable proportioning valve. The rear most port on the master cylinder is really provides positive displacement of fluid because it has a direct link to the pedal while the front port has a piston that provides pressure through a set of springs between the front and rear pistons. This leads me to believe that the front port is not a positive displacement port and can/will vary the output based on fluid pressure/resistance. This has me thinking if the adjustable valve will really work on the rear port ??

Am I just overthinking this or should I swap the lines around before adding the adjustable valve ?
AG.

 

[pacecarta]

after a certain point the front is positive ,the spring is there to return the piston allowing the rear piston to displace more fluid for drum applications

heres a link on brakes when running the race brakes
http://www.markwilliams.com/braketech.aspx

 

[turbobitt]

after a certain point the front is positive ,the spring is there to return the piston allowing the rear piston to displace more fluid for drum applications

heres a link on brakes when running the race brakes
http://www.markwilliams.com/braketech.aspx

There calculator is interesting. When calculating the Foot lever ratio for 120o PSI and 1.032" master it comes up to 6.72:1 and is much closer to the 7:1 ratio (my actual pedal ration) compared to the 7.92:1 for the 1 1/8 master cylinder. At least that confirms I'm heading in the right direction for the master.
They do suggest using a pressure reducing valve but for the front. I don't have a problem with the front but the rears will lock up before the fronts. I actually had the car bouncing on the slicks at 150+ MPH because of this. When I had the stock brakes and big ford 11" drums the brake bias was perfect and actually stopped really good.
AG.

 

[pacecarta]

i have mine setup standard line routing using strange 4pistons at all corners and the 1 1/8 bore MC
on a pass that should have only been an 1/8 mile run i forgot to brake after the 1/8th and had to grab the brakes hard and skidded my fronts (26x6.5 MT sr radials and mt pros on back . they recommend that the fronts be cut back on drag application where front traction is limited .
who knows if your fronts may have been locked while you were bouncing the rears . knowing the pressures at the wheels would help with that , maybe hook sensors into the xfi they have a kit for reading the pressures at the brakes ( http://www.summitracing.com/parts/str-p2360 ) if you know the rears are too high vs fronts putting an adjustable valve on the rear would work ,

i dialed in one setup that had 1600 psi at the corners (vac brake, skinnies and 325s , track only) so i dropped the fronts to 1200 with a wilwood adjuster on the front line

you could flip the lines and add a valve to regulate the fronts

 

[turbobitt]

i have mine setup standard line routing using strange 4pistons at all corners and the 1 1/8 bore MC
on a pass that should have only been an 1/8 mile run i forgot to brake after the 1/8th and had to grab the brakes hard and skidded my fronts (26x6.5 MT sr radials and mt pros on back . they recommend that the fronts be cut back on drag application where front traction is limited .
who knows if your fronts may have been locked while you were bouncing the rears . knowing the pressures at the wheels would help with that , maybe hook sensors into the xfi they have a kit for reading the pressures at the brakes ( http://www.summitracing.com/parts/str-p2360 ) if you know the rears are too high vs fronts putting an adjustable valve on the rear would work ,

i dialed in one setup that had 1600 psi at the corners (vac brake, skinnies and 325s , track only) so i dropped the fronts to 1200 with a wilwood adjuster on the front line

you could flip the lines and add a valve to regulate the fronts

The backs are definitely locking up. It does it on the street with the street tires also. It probably doesn't help with my car being so heavy. The fronts are skinny but a lot of weight up front.
AG.