911 SC brakes, 19mm MC combo question Options

[RoadGlue]

Hi everyone,

I've recently entered the world of bigger brakes, and hoped I could get some feedback here about proportioning valves. I have a set of 911 SC brakes ready to be mounted, and wondered if I'll get the correct brake bias by ditching the stock proportioning valve. I have the "T" fitting, but wonder if I shouldn't put an adjustable proportioning valve inline. Seems like it would always be better to have an adjustable proportioning valve, but is it absolutely necessary with that brake configuration?

Mmmm, brakes.

Thanks!

Randy

[lapuwali]

QUOTE (RoadGlue @ Apr 4 2005, 11:18 PM)

QUOTE (mrihop @ Apr 4 2005, 11:09 PM) If you're going to do a 6 or 8 cyl conversion, go to the T fitting.  Otherwise keep the proportioning valve in it. What consequences would there be by taking the stock valve off when running a hopped up 2.0 4-banger? How does the extra weight of the 6-cyl or V8 factor into the equation? I'm running stiff suspension (180# rear springs, 21mm torsion bars, 22mm adjustable sway bar, poly bushings) if that matters at all. Thanks for the answer, I just like to know "why." Best, Randy

This subject has been discussed in detail, multiple times.

In short, a prop valve will only help you if your rear brakes are more powerful than available traction in back. There is some weight transfer forward under braking, though the effect is smaller on a 914 than on many other street cars because the CG is so low already, and the car starts out with a slight rear bias. With the SC brakes up front, you will have a great deal more braking power up front, so you'll have (on balance) less in the rear. This means any prop valve will be less useful, and probably not at all useful. This is why fitting a T is usually done when big brakes are added to the front, to try and add back some of the rear brake bias that's lost by fitting big front brakes.

It's pure speculation on my part, but I feel that fitting big brakes only to the front of a 914, esp. if you're doing anything to add weight to the back (like swapping in a V8) is not going to give you the best possible brakes. Adding big brakes also to the back and fitting an adjustable prop valve to tune them will very likely result in significantly better brakes that will also be more stable. I have yet to test this theory myself, though SirAndy has fit large rear brakes and found a substantial improvement.