Cobra Brakes
 

The only remaining weak spot on CSX3170 are the brakes. The car tends to get a little unstable under heavy braking with ideal rear bias or does not stop well at all if the bias is shifted forward for stability. We consistently get higher acceleration G's than braking G's which is odd since two wheels accelerate and four wheels brake. I finally bit the bullet and installed a Bosch Racing MK5 ABS system. It was very difficult because I had to design and have fabricated the sensor mounts, wheel speed tone rings and ABS pump/solenoid mount along with front and rear pressure sensors and individual brake lines to each wheel cylinder and from both master cylinders. I started in July and finished last Sunday, first track test is next week. This system is competition only and has 11 driver set positions depending on conditions. There will be no "ice mode" so it should be good. It is used on Porsche cup cars so is quite well developed.
It includes a centrally mounted yaw sensor so should keep the car straight under high G stops. It has passed all the internal system checks with no error messages from the Bosch computer. I am hoping this takes the car to the next level. I mounted all the components using existing bolts brackets and tie wraps so the car was not modified for ABS. I sure hope it works lots of time and effort invested! It is user programmable and includes tire diameters, track width, wheel base, wheel mass and 2wd, fwd, or 4wd.
It also recommends ideal brake bias settings using the pressure sensor output and my bias bar adjustment.

Bruce

Do your brakes ever get hot enough to be effective at a Autocross.....?

Amazing you can do it as just a bolt on. Eagerly awaiting results of field test run

Not in my experience....you really just need nice soft street pads.

Morris,
Rotors go blue, so yes they reach correct temp for the pads I use. Not a friction problem just difficult to modulate at low speed problem. They lock up especially fronts on turn in. Add rear bias and the car steps out at rear under high decel. Have tried about 10 different pad compounds and the Porterfields I use now have been the best. Hoping we can just Jam the pedal and have Bosch handle modulation like we do in GT3.

Have you ever used temp paint on the rotors to help balance the brake system....and are you using a Balance Bar....or a Proportion Valve.....

Brake system balance
 

I have never used a proportioning valve because I don't like the face that they limit pressure. In the 1960's through 1990's I drilled holes in the balance bar at different locations about .030 apart and carried 5-6 bars with me so that I could alter balance by changing the bar to accommodate different surface conditions or pad material. Around 1995 I installed an adjustable balance bar and have used it ever since. This is not a balance issue it is more of a modulation issue because you start with almost cold rotors and pads and then come in with very hot rotors and pads so the coefficient of friction changes through out the run. When I ran the car at Laguna Seca in 2012 the brakes worked perfectly because they were on a road course and retained heat so that the coefficient of friction was more stable. Autox is a very different sport because you have to adapt to pedal pressure changes through the run as they heat up. I have played with master cylinder bore diameters, pedal ratios, and pedal position and size to improve braking performance for quite a while so the manual system is fairly well optimized.

The ABS system allows you to brake into the apex with out a lock up, something the best driver in the world cannot do with a standard brake system. It can also release a wheel or a pair of wheels to keep the car straight during max deceleration.
Scott is very, very good but even he can't beat a competition ABS system.
The car stops very well now, I just want more and brakes look like the next low hanging fruit. We are on 200 TW tires which also contributes to our braking difficulties. Yes I have temperature paint, but only used it on road courses.

I agree regarding the the proportion valve....and we used what we called trail braking at many of the tracks especially when we went into a carousel turn.....I learned that because we went into the carousel to fast and experience became our best education.....:eek::eek:

Morris,

I have started practicing with trail braking and I think it helped my times the last time at Watkins Glen. I wonder if trail braking early in a run might help warm up the brakes sooner during an autocross event? Do they let people drive around the area prior to their turn so that you could ride the brakes a little and warm the up prior to the run?

Jim

Trail breaking helps shift vehicle weight forward which aids turn in, but if you apply too much brake you can either spin or lock the front inside wheel or create severe under steer. My point about an ABS system is that you can really jam it in to a corner with out locking inside wheels, spinning or getting big under steer. A non ABS car can never brake as hard into a corner as an ABS car because when a wheel locks steering is gone.

In an autox you want to maximize everything so there is no opportunity
to warm your brakes without giving up time. We try and pre-warm the fluids by driving slowly with the brakes on in the pits but you never get near brake operating temperatures. In a road race car you get a couple of laps to warm brakes, fluids and tires so a very different ball game. One mistake in an autox and you lose there is no ability to make up time on following laps.
I am looking for an improvement, the brakes are currently equal to or better than our Goodguys competition, but CAMS it is a different story the C7 Corvettes are killing us under braking with their ABS systems.