Monthly Archives: February 2015

Brake

Stoptech Rotor Swap

The rotor hats on my Stoptech rotors started getting cracks on them.

picture of stoptech aero rotor hat cracksThis is a well documented problem with some of the Stoptech aero rotor hats so I had been keeping my eye out for the problem to arise on my rotors.  Interestingly it was only the passenger side rotor that had these cracks, the driver side was still in good shape.

With a crack as extensive as the one shown here I decided to replace the aero rotor hats.

picture of stoptech aero rotor hat crackAbout the time I went looking for a place that would sell just the hats I found someone parting out an S4 who had the entire Stoptech 332 BBK for sale with rotors that had been replaced within the past year.  For just a little more than the rotor hats retail for I picked up the entire kit, including stainless steel brake lines, partly worn pads and a brand new set of pads.

Once I had everything on hand I set about swapping the rotors.  Putting the rotors side by side it looks as though the rotor hat design has been revised since I purchased my Stoptech BBK setup.

picture of stoptech 332 aero rotors being swapped on my Audi B5 S4

This was the first time I had taken the rotors off since having the Stoptech BBK installed in 2004 and I was not sure about how hard it would be.  After looking through the brake kit install guide it was evident the swap should be fairly easy, which it was.  For reference these are the two bolts that need to be removed to pull the caliper back so that the rotor can be swapped.

red stoptech 332 brake caliper

The old rotors and newer ones were very similar in thickness so I did not need to monkey with the brake pads at all.  To swap both sides took about 30 minutes, though my wheels were already off and the front end raised for other work I have going on.

Testing

Hitachi MAF Round 2

The disparity between the flow bench readings and the MAF Sensor conversion table, MLHFM, was larger than I was expecting to see even accounting for the rough calculation from kg/hr to CFM.

I checked the 5v output from the ATX power supply and observed that it was providing 5.138v, a good amount more than I would have liked given the sensitivity of the MAF sensor.  I decided that I would try using a dedicated 5v power converter to provide the MAF sensor with its 5v supply.  I had previously checked this other power supply, and due to the ability to tweak the output voltage I had been able to get 5.005v from the device.

maf_power_setupWith the new power supply in place I ran the Hitachi sensor on the flow bench again.

hitachi_maf_flowbenchThis time the results I obtained were:

hitachi_sensor_5pt005v

Based on these results it’s starting to look like I’ll need to tweak the power supply to get the bench readings in-line with the stock predicted values, and then I can move on to checking an 85mm housing.

 

 

Testing

Hitachi MAF Sensor Values

Rearranged the Hitachi MAF housing to have the airflow going through in the correct direction and also attached part of the stock airbox to try and better replicate the on vehicle airflow into the sensor.

hitachi_maf_cfm_vs_voltage

The chart above shows the predicted values for CFM, solid blue line, based on converting kg/hr to CFM; assuming 13.076 cubic feet per pound of air.  The dots are measured readings from the flow bench.

The readings are obtained by slowing increasing airflow, noting the CFM displayed on the digital manometer and corresponding voltage on the multi-meter.

As this was the first time making a full range of readings it’s possible the procedure still needs some improvement.  I noted that with no airflow through the MAF the voltage reading was 0.05 volts.  At the other end, I could obtain voltage readings in excess of 5 volts, recording 500 CFM at 5.12 volts.