parsonsj

I've recently installed a Stack Data Recorder, and one of the sensors I added was a brake line pressure sensor (located ahead of the caliper flex line).

Sitting in the garage, motor idling, I can get about 1200 psi when standing on the brake. That seems low to me -- I'm wondering if I've done something wrong in the installation. Or maybe the ABS controller limits pressure when it knows the car isn't moving?

Anybody know anything about this?

thanks!!

RX-Ben

That number is correct, if anything slightly on the high side.

parsonsj

Actually, I rounded up. I think the number was actually 1168. Does the ABS allow higher pressures at higher speeds?

Or is that the limit of the braking system?

RX-Ben

Coming from the MC is as high as it gets, the ABS modulates (cuts) pressure from there, as needed.

parsonsj

OK, thanks. I wanted to make sure I understood what was going on before heading to the track.

383

I was just looking for a way to log braking on my C6Z
Did you use a kit? It looks like a la carte on the website.
Details of your setup please

parsonsj

No, there's no real kit. You get the recorder, and decide how many sensors you want to hook up. The base recorder (that's what I have) supports 14. There is a dual recorder that supports 22 or something.

Then you buy the sensors you want... or you can (in some cases) cut into the factory sensors and map the voltage to values. I did that for a wideband and for throttle position. RPM and MPH are pretty simple at the back of the instrument cluster.

It was a big undertaking to get all the sensors installed, hook up the harness, and make it all look sanitary. It started as a small project (as they often do, lol) to record transmission and differential temps and to see if more cooling was needed. From there I added oil temp and pressure, water, brake pressure, etc. etc.

Some of that is available in other ways (AIM Solo DL, for example), but this one where I can add whatever sensors I want and and manage the data any way I want.

parsonsj

Some pics...



Here's where I started with the differential temp sensor.




Another view of the differential fluid temperature sensor. I drilled and tapped the case just outside the ring gear.




Water temp sensor is pretty simple. It just needed the Auto Meter adapter for the 6mm straight threads on the sensor.




I picked up the TPS here. That's still a work in progress.




The whole harness had to be pulled back so that the instrument cluster can be put back into place without rattling or wires rustling. The wideband controller is on the far left (red box)




The recorder itself is tucked way back behind the instrument cluster, above the throttle. It is secured with 3M Dual Lock to the column brace.

RX-Ben

Depending on which TPS wire you pulled from, the voltages will go in differing directions when the pedal is pressed. You'll also notice WOT voltage variation at speed vs when parked.
As a future reference, you can use a pull-up resistor (which requires a 5V output from your logger; use of the pull-up resistor will result in a ~0-5V output instead of a variation in ohms) for temp sensors, to allow the use of a cheap one wire Autometer 2259 temp sender - very compact (just threads, no long snout like most fluid temp senders) and $12.

Bill Dearborn

With ~ 4 sq in of piston area in a stock C6Z front caliper or an aftermarket caliper you are seeing >4700 pounds of pressure being applied to each brake pad. That should be plenty.

Bill

parsonsj

I agree that that seems like plenty. Maybe it's fine. Or maybe not. 4700 pounds of pressure means... what's the design limit of the pads, the rotors, and the calipers?

As an example, on a previous project, using similar calipers (Wilwood 6 piston on 14" rotor, custom pedal, manual master, balance bar, etc.) I was generating 1800 psi at the caliper or over 7000 lbs of pressure per brake pad. That setup didn't have ABS.

I think the ABS is bleeding off pressure, because I can get to that 1168 with relative ease, and no matter how much harder I push, I don't get any more pressure. In fact, I think it goes above that, and then drops down but it's hard to say for sure.

My concern was that the sensor is plumbing has trapped air in the line, or that the extra fluid volume in the path between the ABS controller and the caliper has upset the ABS calibration.

parsonsj

Thanks Ben. Interestingly enough, my Stack dealer didn't mention that option, lol. Instead, he sold me sensors at $99 apiece. Live and learn!

0Todd TCE

Not sure how these numbers are being calculated but nobody should be seeing 1800 psi of line pressure to a caliper. Even under high spikes that's a huge number.

Every set up is slightly different but I'd put numbers in the 700-800 range being more realistic. While my background is more open wheel stuff it took only about 450 to pull over 1G on a car with slicks when we did some data years ago.

parsonsj

Thanks Todd. That's good data. 1800 psi was measured with an Auto Meter gauge with me putting all the force my 45 year old body could muster on the pedal. It wasn't measured on the track that high.

MySR71

Does your car have a brake pressure sensor as part of the ABS unit (the C5's do)? If so, can you splice into it?

RX-Ben

from what I could tell, C6's (at least w/Delphi ABS) do not have the pressure sensor.

96CollectorSport

Ben, the 05-08 C6's do have an external pressure sensor (it's on the inboard side of the ABS valve body - toward the engine).
The 09 and up Bosch units do not have an external pressure sensor.

0Todd TCE

FWIW (and i'm not picking an argument here just supplying a resource)

Use my Dual MC calculator and start with the weight transfer table. From there put in your brake data and then select perhaps 60-70 lbs of leg force applied. *It's not a boosted design but you can see what the required rotor torque is necessary to achieve your max decel. From there just back into the line pressure value and see what it is.

**You'll need to set both MC bores to the same spec (1"?) and set the balance bar pivot offset to ZERO which will then make it essentially a singe mc design pedal.

Curious to what you find.

MySR71

Ok. It isn't brake pressure, but if 383 wants to know when the brakes are on/off, maybe he could tie into the brake switch which turns on the brake lights.

parsonsj

Thanks Todd. I played with the calculator for a bit tonight. Great tool!

I *think* (because I guessed at a lot of values), that 1100 psi on the front brakes equals about 1.7g of decel, which is probably way more than my tires can handle. Which is good to know, because I can measure that on the track now, since the Stack MFR has 3-axis accelerometers.

Anyway that puts my mind at ease. It seems I've probably not adversely affected brake performance with the additional sensor.