Did a track day last weekend with my Z. I have the 13" Stop Tech BBK on the front and Hawk HPS pads on the rear with OEM non Brembos. The Hawk pads didn't hold up well under track use and left lots of uneven deposits on the rotors that now cause the car to shutter as I come to a stop.Tried using garnet sand paper to remove the deposits but didn't improve the condition any.
Had this same thing happen last year after a track day with all stock brakes and the sandpaper cleaning on the rear rotors worked that time.
The edges of the Hawk pads crumbled away from being over heated so much.I havn't seen any higher performance pads available for non Brembo rears.

 

search is your friend. there have been many discussions on pad choices, and at least a couple specifically about oem non-brembo rear options. here's one:

https://my350z.com/forum/autocross-road/123331-rabyestos-st43-pad-review-and-melted-piston-boot.html

ahm

 

What you are probably experencing on your rotors is cementite. Once it forms you can't get rid of it. Even resurfacing by grinding is only temporary. New rotors are the answer.
I'm surprised you're still getting rear bias with a front BBK. For track sessions I used R4's from Porterfield in the rear. Very hard and need to get hot but anything else would disintegrate quickly. R4S's worked for the street. They are aggressive but don't require higher temps to work.

 

Also, try cutting off the dust shields off the rear end. They seem to act like a heat sync and keep heat in from the inside of the rotor. You must have already cut down your fronts when you installed the BBK. keep us posted.

 

+1 for replacement rear rotors and also cutting off the dust shields. I bought the Stillen slotted rear rotors and they were good even with the Hawk HPS pads - much better heat dissipation than the stock rotors.

 

Thanks for the replies. I did do a search on brake pads and skipped thru all the posts that looked interesting. Don't have time to sit around and read every single post on pads.
I talked to the guys at Stop Tech and they suggested i just replace the rear rotors with their slotted ones. I agree but I hope to install the BBK in the rear some time in the near future and that $210.00 for replacement rotors could go towards the cost of it.
I'll cut down the dust shields now as suggested since it will need to be done some time. Thanks

 

if you're thinking about removing the rear dust shield--

the sheild portion is actually spot welded to a 2nd piece that's then attached to the hub.

if you cut and peel the sheild back (somewhat like a opening a cupcake wrapper) you can get a chisel in there and then pound @ the welds with a rubber mallet and you can get a clean seperation of the dust sheild from the hub, rather that having jagged edges after using a metal shears or rotary cutter... just wear ear plugs cuz the hammer resonates in the fender well.

 

thanks chebosto!