Brake Pressure Regulator in Vintage Race Car Options

[jhynesrockmtn]

Hi, I am in the process of refreshing a 914-6 GT tribute car that was built for PCA solo events in CA and has been mostly in storage for several years. The engine is a 2.4 that was built by GD racing in San Bruno. The suspension and brakes are 3.2 Carerra. I pulled the calipers and they are at PMB. New soft lines are going in. I was somewhat surprised to find the stock 914 brake pressure regulator still in place. There is no after market proportioning valve.

The car will be used a few times a year for vintage wheel to wheel and then some PCA DE events. I have several years of experience racing vintage FV. As I got older and saw several buddies get involved in some nasty open wheel tire to tire incidents I decided I wanted fenders and more metal around me.

I am not the most aggressive driver in the world and this car will remain street legal. I also want it to remain as period correct as I can get. I don't want to go down the rabbit hole of cutting a ton of metal out of the car, etc.

Should I pull the regulator and put a T in and proportioning valve in the cockpit?

Should I leave as is and see how it performs? If I leave it I will send to PMB to have them rebuild it.



Cheers, Jerry

[stownsen914]

If you a google search, you'll find a lot of discussion on this topic. I have a similar question, as I just bought an old 914 SCCA racer that also still has the stock "proportioning" valve (it's really a spring loaded pressure limiting valve). I noticed that Eric recommends keeping the stock valve, and I see he rebuilds them. I'd think that it would be a good idea for a track car, to replace the stock valvue with an aftermarket one like a Tilton valve, but I'm not informed enough at this point to say if it's a good idea. Brake bias is highly dependent on which calipers you have and tire widths, and I'm not familiar with the Carrera caliper setup on a 914. Hopefully others will chime in.

I've also wondered if the Tilton style valves are really a good solution to limit rear brake pressure, since I believe those valves are more of a flow restricting limiting valve. I'd think that pressure would eventually rise in the rear brake circuit with one of those if you are on the brakes for a couple seconds or more, but maybe I don't really understand how they work. Curious if someone here knows better.

I can tell you that too much rear bias on a track car is very dangerous and to be avoided. I've driven a couple race cars with dual master cylinder setups, and have experienced rear lockup before the bias was dialed in. You can lose control of the car in an instant if you lock up a rear wheel.

Scott

[jd74914]

I've also wondered if the Tilton style valves are really a good solution to limit rear brake pressure, since I believe those valves are more of a flow restricting limiting valve. I'd think that pressure would eventually rise in the rear brake circuit with one of those if you are on the brakes for a couple seconds or more, but maybe I don't really understand how they work. Curious if someone here knows better.

The Tilton proportioning valves are proportional pressure regulators; not flow limiters (like a variable size orifice, etc.). The attached image shows a chart of a lever-style valve. Their action is quite similar to the OEM valve, just with an adjustable knee point.

Note: All valves will have some initial flow limiting effect, but you're likely not to notice too much when you're really on the brakes hard. Stopped and just pushing in the brake pedal, perhaps, as already noted in some above posts.