Brake propotioning valve installation

[porsche735]

I am building a car for spec911 Porsche Racing Club - Spec911 which allows any kind of brake proportioning system. I also use teh car for time trialling which does not allow driver adjustable brake bias. I am looking to build a setup for my car that allows cockpit adjustment with some sort of cover or lock to make me legal for the time trial events. Can you please post some pictures of your cockpit adjustable valves with any information as to why it works or doesn't for you?

Thanks,
Chris

[Walt Fricke]

Chris

If you install a balance bar system, you can easily disconnect the adjuster cable from the bar. All it takes is loosening a set screw. You could pull the end out of the way to where an inspector could see it.

A pressure limiting valve would require, as you are thinking, a secured cover. From the lack of response to your post, you may be the first to care about this and on your own for design.

How about a pressure limiting valve under the front hood, where you can't get at it? Do you really think you can feel the difference in braking between the weight of gasoline you have at the start of a race, and what it will be at the end, and in a car of this relatively low level of sophistication? Once you find the bias you and your car need, can't you just leave it set there? You might even consider the 3.2 system, with different "capsules" for different rear brake pressure limits.

If you need adjustment mid-run, you are certainly a much better driver than I, Gunga-Din. I have a cockpit adjustable balance bar, and have yet to reset it during a race. Occasionally fiddled with it during practices and such.

Walt

[Jeff Alton]

I run the Fabcar unit with dual MC and balance bar I can adjust from the cockpit. Not sure this is what you are looking for or weather you want a pressure limiting valve.

To date I have only run my car at DE's where I start with a full tank and run till it is close to empty. I do adjust it during the day. I will be racing the car starting in the spring and figure that I will be like Walt, not adjusting it during a 20-30 min race.

Cheers

[Cory M]

We have a racecar that came with a tilton lever type adjuster mounted next to the master cylinder under the hood, probably due to the rules...

[RaceProEngineer]

Chris,

If one of your questions is, "Which is more effective?", then the answer is the TIlton-style balance bar between two master cylinders.

And if your time trial rules state, "no DRIVER ADJUSTABLE" proportioning devices, then Walt's first suggestion is probably best - a balance bar, with the knob and/or cable removed from the cockpit for the time trials.

However, most sanctioning bodies that prohibit adjustment in certain classes do so because of the ADJUSTMENT CAPABILITY itself, and not simply because it can be done while on the track. Make certain of the fine points of the regulation before investing.

Ed LoPresti

[Walt Fricke]

Chris

Following Ed's lead, I took a quick look at the GGR TT and POC TT rules, based on where you live as a guess. I found where you might have to change your class by altering your brake bias mechanically (i.e., other than by using different pads front and rear), and a prohibition on driver adjustable wings and such. But nothing on cockpit adjustability. I'm not expert on those rules. And Cory's post suggests somebody has such a rule.

What part of whose time trial rules affect you? Just curious.

Walt

[Cory M]

The balance bar is the best solution, but it requires you to change to a custom dual master cylinder setup, which is expensive and may not be legal in your class. Smart Racing sells them. Of the valve type adjusters the knob style will give you finer adjustment than the lever, but the lever clicks into place so it's more repeatable. Tilton has a pretty good explanation of how they work in their manuals available at their website.

[911st]

A balance bar system is the best as noted.

If going with the proportioning valve you might want to look at your stock brake balance to begin with. If the rear is under sized from the factory adding proportioning valve to the rear is not going to help. If you have increased the percentage of tire in the rear you might be even ore under braked in the rear. If this is the case you would want to add the valve to the front. I knew of one club car that did this.

The 3.2 Carrera system has what we might call over-sized rear piston size that is limited with a factory in line limiting valve. Porsche did this to get faster rear brake pad engagement but limited it to retain a proper front and rear balance. If you go to this system and put a proportioning valve in its place you should have some usable range of adjustment.

I guess what I am saying is adding a P-valve may not add any advantage. Another way to balance up the system is to play with the pad material choices front to rear.

[porsche735]

Thanks for the replies. The system going into the car is 944 front brakes with stock 1989 Carrera rears and no pressure limiting valve. The GGR rules allow the use of a proportioning valve, but it cannot be cockpit adjustable. However, the spec911 rules allow for cockpit adjustability. As I have the floors out for replacement and have access to the center tunnel, I am asking where people mount their proportioning valves in case I should do something while I have the tunnel open. Apparently, no one does this.... My thought was to put something in the middle of the tunnel between the seats while I am in there. And, to meet the rules for DE, to put a locking box over it. Perhaps I am getting too fancy.
I am focused on this as I just completed the 24 hours of LeMons event with 4 other drivers and we were chasing the elusive bias adjustment the whole time....

Thanks,
Chris

[Jeff Alton]

Ok,

Your approach will only allow you to decrease the rear brake pressure, (or front brake pressure if you re routed the lines) which may or may not yield the results you are hoping to find.....

You could mount a dual mc Fabcar unit (from SRP) with a dash mount knob. Then when racing in a series where cockpit adjustment is not needed, you could remove the knob. It is held in place by a set screw.

[Walt Fricke]

Chris

I'm guessing that your LeMons car was not fully sorted before the event. But your Porsche will be before its events, so you will have some testing time to make any adjustments to its bias that you need without having to have cockpit adjustability.

Just guessing. Maybe your team spent two years and a hundred test hours on the LeMons jewel?

Walt

[Mahler9th]

Hello Chris:

We live not too far apart, but I am not sure if we have met. I am a member of the GGR and race with the PRC. Have you pinged some of the locally available resources on this question? We have a lot of 911 'Spec" class cars in the area and the owners, drivers and builders are a friendly bunch. I am sure there are various approaches to braking systems, and I am sure that folks would be happy to share their ideas and experiences with you. Many do not frequent these forums or Rennlist (which are both great resources). If you join the PRC (which is free), you can post a message on the forums there. Some will likely respond.

As you probably know, the GGR also has forums, so that can be a great local resource as well.

I am not sure what the current practices are in terms of brakes on a 911 configured for our Spec Class. Brake system design can be kind of tricky in the heavier cars like the Spec configuration (solutions for a 1950 pound car like mine are trivial in comparison). I am not sure there is an optimal approach with 944 or 951 parts, but of course I could be wrong as I have not done any research.

The guys up at Rothsport in Oregon may also be a valuable resource as they run a flock of 911 Spec cars with PRC.

Good luck and happy holidays,

Mike

[Flieger]

Which dual master cylinder setup is correct for a 1971 911S? On the Tilton website, they do not specify applications for their master cylinders.

Also, does the balance bar come with, as a kit? I am looking into my future upgrade "wishlist."

I so not see these products in the Pelican catalog, otherwise I would get them here.

Thanks for any info.

[RaceProEngineer]

Tilton? How about calling them?

I have 805-688-2353 as a technical information number. We have not had occasion to speak with them for quite some time, but they were always very knowlegable and helpful.

They are on your coast!
Ed

[Flieger]

It does not need to be Tilton, I just hear their name so much in this sector of performance parts.

What is the best brand?

[JP911]

Originally Posted by Flieger

Which dual master cylinder setup is correct for a 1971 911S? On the Tilton website, they do not specify applications for their master cylinders.

Also, does the balance bar come with, as a kit? I am looking into my future upgrade "wishlist."

I so not see these products in the Pelican catalog, otherwise I would get them here.

Thanks for any info.

The 901 shop makes a dual master setup for non-boosted cars (assuming you haven't converted to boosted brakes on your '71).

[Flieger]

Cool, I know that name. Yes, just my leg power for the brakes.

Wow, that is more than my upcoming suspension refresh. I guess it will remain on the "to-do list" for another day.

Looks nice 901 SHOP Product 2

[Walt Fricke]

Flieger

Take a look in a Pegasus catalog. There is a Tilton floor mounted system shown. Also an overhead mounted one. Overhead mounting is popular for stripped out, full on track GT cars. Lots of extra effort in rerouting clutch and accelerator actuation, etc. if you move those up, as you probably would. Lots easier to service and adjust, though. Anyway, Pegasus prices not quite so jaw dropping,

Smart Racing sells (or sold) a Fabcar kit which is a bolt-in for cars with boosted brakes (pre-ABS). Pretty straight forward installation on later cars. Cost in the 05 catalog was less than half that of the 901 system. It can go into earlier cars with some reinforcing and hole cutting, plus the pedal cluster from one of the boosted cars. SRP's install instructions discussed this.

The RSR clone setup from 901 is nice, but my reaction is also "wow" to the cost. No doubt if you could even find the factory bits (I have an old Andial catalog which lists that, if I recall), they would cost even more.

I can't tell from the 901 catalog photo, but I'm guessing that the modifications to the clutch pedal were made to allow the adjusting cable to come in from the left. On my car, I had to bring it in from the right so there was no clutch pedal interference. This was a compromise, as there is some rubbing on moving parts (the short clutch cable lever in the tunnel, and the accelerator rod)on the right side, but not enough to cause any issues. Looking at Pegasus, I see Tilton now sells a right angle adapter, which could be installed to avoid these issues.

I think the 901 folks are not quite right in saying that no chassis modifications are required for their floorpan mounted system. The firewall has holes through it for the stock MC and mounts. To mount two MCs you have to drill some more holes. Not, however, a big deal. Anyone who can't do that isn't going to be installing an aftermarket system like this by himself anyway.

If you can weld, you can make up your own RSR style setup, and at not too much cost. You will have to purchase two MCs. I like the Girling - aluminum and short, as there is not an abundance of space. That is what 901 uses. And a balance bar. Pegasus sells the Tilton for $60. You have to refashion your pedal cluster sheet to hold the two MCs You should also weld in gusset reinforcements - remember the 914s whose firewall flexes when brakes are applied heavily. And you have to weld in the balance bar itself to the brake pedal arm. Then rework the firewall so things line up and you are good to start replumbing, which is not too hard. When I redid the balance bar setup which came with my well used roller 911, I had to do rather more work to include a 3d MC (for a hydraulic clutch), but doing a copy of the RSR setup isn't all that complex.

But it is not just a turnkey setup.

Walt Fricke

[Flieger]

Someone suggested an adustable proportioning valve. Can anyone give some insights into a lever/dial proportioning valve? (Not a step type limiter like the Carrera setup)

Can my rear M calipers provide a greater rear bias with my front S alloy calipers?

[911st]

Flieger,

This is what I noted.

Originally Posted by 911st

...The 3.2 Carrera system has what we might call over-sized rear piston size that is limited with a factory in line limiting valve. Porsche did this to get faster rear brake pad engagement but limited it to retain a proper front and rear balance. If you go to this system and put a proportioning valve in its place you should have some usable range of adjustment.

...