OP, your car does sounds well setup (aka badass). Our cars are actually very similar minus your custom fuel cell and abs (nice). Any pics of your brake cooling setup?
Ideas:
-Ride height (and effects)
-Front vs. rear tire temps off, perhaps exacerbated by the amount of rear toe? (And dynamic toe?)
-I also run 1000lb fronts but run a 550lb rear spring on my true type AST 5200s (with JRZ top hats
).
I'd bet a nickel, though, that its due to the rear loaded tire operating in an unfavorable kinematic situation, as you said. I've noticed a big change in rear grip from ride height changes. Also keep in mind that rear toe changes with suspension position as well, so perhaps not just a camber curve issue. After making a rear rideheight change before my last track day -to help combat inside rear wheel lift on some offcamber corner exits- I was battling a lot of oversteer everywhere. I tried softening the rear ARB but absolutely hated the rear roll amount that introduced and just went back to the mid setting on my whiteline rear, made a small tire pressure change and just drove around the oversteer. Discovered one of my damper adjusters was broken and I had forgotten my spring perch wrench at home
From looking at your car pics sort of looks like you have SPL solid rear subframe bushings? I have those as well with the OEM'ish spacer setup at the moment.
Anyone feel like measuring hub centerline to rear wheel arch distance and alignment settings and collaborating on establishing an optimum rear ride height range?
Also: Get on the "370z Top Ten Track Records - Road Courses II" thread! The only times I've got up there, with the car as set up as it currently is, are from the Ridge MSP unfortunately.