toolo4sno

This thread is for reviewing the AP Racing front BBK (4pot Comp./325mm) that fits the B5 S4 chassis. My kit was sourced from Eagle Motorsport (*Blue-Angel*-AZ member). I saw some of their parts on the classifieds section, did a little research and scooped up what they had. Blue-Angel was also able to help me source other brake parts I needed.

AP Racing BBK PNs
Calipers: CP8350-24S4L/25S4L
Rotors: CP3908-102/103GA
Street pads: APF405
Track pads: APF403

I was looking for a BBK that could bring me a days worth of fun at the local track without absolutely having to bleed brakes mid-day. Obviously increased stopping performance with minimal loss at the end of sessions was also important. Swapping pads had to be simple and not require rotor sanding. The street pads had to dust as little as possible and not squeal at low speed stops; while the track pads shouldn't eat up rotors. The setup had to bolt on with minimal modifications. Preferably no knuckle grinding. I use 17" rims; so a massive rotor wasn't an option either. All that and I didn't have a ton of money to spend. This was easily shaping up to be my most expensive upgrade. Yet a sorely needed and overlooked upgrade.

Up until this past Friday I've run track days in my '02 S4 with the stock HP2 brake setup. Upgrades to fluid eventually lead to installing front brake cooling. On hot days a bleeding was still required. Aside from bleeding brake fluid the pedal feel/reaction time had been slow and disappointing from day 1. I had been using Hawk HP+ pads up front and HPS in the rear. When switching to street mode I swapped the HP+ to HPS. This required a rotor sanding between changes and made conversion from street to track modes time consuming and annoying.

The install of the AP parts was pretty straightforward. I did have some questions on torque figures and some install tips that Blue-Angel was able to answer. Once you get the stock parts off there is so much more room to work. The AP calipers are generally smaller and of course, lighter. Definitely a plus for a notoriously tight vehicle. I'd give install difficulty a 3 of 10. Nothing really difficult about it at all. The OE brake caliper and rotor weighed in at about 34 lbs. The AP Racing kit is about 28 lbs; so a decent 6 lbs loss of un-sprung weight.





One issue I did have after install was clearing my main set of wheels. The calipers cleared the OE wheels, and my dry track day Kosei wheels (17x8, et35). The calipers did not clear my August Werkes (18x8, et30); which I use for summer street driving and wet weather track days. After a try with a 6mm spacer; I felt it was best to go to 7mm. This gave me just under 3mm clearance from rim to caliper. I also did not experience any fender clearance issues as I feared by adding that much of a spacer. The inner fender lip is rolled on my car; so that helped.



Using 6mm spacer. Ended up using 7mm for more caliper clearance.


The first improvement I noticed was the immediate reaction of the pedal. I was never impressed by how much pedal travel it took the HP2 calipers to register any braking force. It seemed like you had to push more than an inch to get any useful braking. Now with the APs installed a reaction is virtually immediate. There is also an appropriate and progressive increase in stopping power with more pedal.

The APF405 pads stopped very well for the street. After 100+ miles or so of street driving I can say the low speed squealing is a little too much for my liking. It's very similar to my HP+ pads from before. I've been told that bedding the pads better may alleviate some of that noise, but nothing has quite happened yet. Also, the floating nature of the rotors produces it's own noise. At low speeds on the street they make a slight rattling noise. I'm sure I'll get used to it, but it caught me off guard at first. It basically sounds like something is loose and rolling around down there, because in theory the rotor is. I can’t say the APF405 pads dust less than the previous HPS pads. More time is needed to determine that.

On to the reason I bought them. Overall, the AP Racing kit worked very well at the track. Pad change over was quick. Since I changed to slicks the car was in the air anyway. One bolt, some pad wiggling and the 405s were out. Then a little shimmying in the 403s, bolt on, and it was good to go. I’m not sure if it would be a little harder with old worn pads going to newer thick ones. I brought squeeze type clamp to push in the caliper pistons to clear it just in case. Blue-Angel set up the rotors with 3 paint splotches to help determine if the brakes are at the correct temperature. WHRRI is not the fastest nor most brake heavy of tracks; so I only changed the green strip white. The orange and red stayed. I imagine for a place like Grattan I’ll probably get more heat in. Orange to white on the rotor edges would be ok, but the red should stay red.



The entire duration of all four sessions at WHRRI were brake problem free. I didn’t even think about bleeding my brakes and temps hovered around 90-95deg F with tons of humidity. I could brake about 50 meters later with the APs on vs the OE HP2s with HP+ pads. It’s possible I could take that even further, but I ran with passengers for most of the day. It was a little difficult to determine if lap times improved much with the passengers, but I believe I will see faster lap times and smooth trouble free running at future OTDs.

On a side note. Removing Fuse #42 (ESP) helped immensely. I was worried with extra clamping power that the sudden intervention of ESP, even when “turned off”, would create bigger problems than with OE brakes. I didn’t have one ESP intervention all day. No problems. Removing Fuse #42 is a big recommendation for people serious about track running. That stealthy ESP intervention when you trail brake late is a very alarming, unfriendly experience.

Pros:
One bolt pad swap
No modifications needed to install, and relatively easy
Pedal feel reaction is superb
Brakes flogged all day in 100+ heat index weather
Anodized finish (my OEs were painted black with G2. They chipped and turned nasty after the first OTD, paint on brakes is a no go for a track car IMO)
Street pads and track pads are compatible material; so no rotor sanding

Cons:
Getting used to $500/pair for replacement rotors
APF405s squeal a little at low speed stops
Slight rotor rattle from floating design
Two out of three rims fit over caliper. Other required 7mm spacer.
Double the bleeding with double the pistons.

This is an ongoing review. When I hit the track again and have a something to note; I’ll add it. That and other street driving observations will be relayed here.

I have every video from every session I’ve run. You can see for yourself. All track days before 7/19/13 were with the stock brake system. Keep in mind 7/19 was also the first time I ran with passengers; so not quite an apples to apples.
http://www.youtube.com/user/2lo4sno