Stage 3: track car now?
End track-hours: ~60
End Laguna Seca time: 1:46-high
End parts/specs:
Diffsonline 3-clutch LSD
Derlin subframe & diff bushings
Hotchkis swaybars -- 32 mm F, 19 mm R
Front tires: RE71r 245/40/18 on 8.5x18 ET35 Apex SM-10 wheels
Rear tires: <same as before> + 3mm spacer
Stoptech 340x30mm slotted front rotors
-3.0 camber F, -2.2 camber R, a bit of toe-in
So, I wanted to tame the rear axle a bit, and a diff and solid subframe bushings sounded like the natural next step to get things a little more planted and predictable. This was probably the last time I had some concerns about "streetability" , especially around the rough ride from the bushings (joke's on me -- the diff I ended up with is way less streetable). At the end of the day, I realized I was already pretty obsessed with the whole racing thing, so decided to stop worrying and sacrifice the car to the track gods (and maybe one day sell it as a racecar, with the appropriate expectations).
For the diff, I talked to Dan at Diffsonline (his work came highly regarded everywhere) and we settled on a 3-clutch unit with the 30% lockup and 45/45 angles. Dan discouraged me from changing the gear ratio (from 2.81 on the AT to 3.06) saying that for other customers, the transmission ECU didn't like changes more than ~8%. In hindsight, probably a better idea anyway -- the B58 has heaps of torque all around the rev range.
The "while I'm there" thinking (dropping the subframe and the diff anyway) also led me to change the diff bushings to derlin. And look for a beefier rear swaybar. But then only a monster would change the rear bar and leave the front one stock (especially trying to cure oversteer)... Sigh... I'd promised myself no more speculative modding... That led me to a fairly beefy front bar for our chassis (Hotchkis, 32mm) and their corresponding rear bar (19mm). The endlinks I ended up with to get rid of preload at this height were 12.5" front and 6" rear (measured at the shortest length, ball joint to ball joint).
I tracked this config for a while without any major changes. With the massive swaybars, things were quite more planted through corners. I could feel the diff doing its magic coming out of the hole and rolling on the throttle. Oh, I could also hear the diff -- like, a lot. I am running the stock exhaust and from inside the car the diff whine is still a fair bit louder than the engine.
The off-track excursions decreased somewhat, but would still happen every once in a while. The car was still reasonably snappy, especially around mid-corner, transitioning from understeer to oversteer. As I mentioned, it would take me an accidental wet day setup (less rebound damping, less front swaybar) to get it better sorted when sliding.
Speaking of understeer, this tire combination (235, 265) was pushing a fair bit on entry. I learned how to trailbrake fairly deeply to get the car rotated. That, plus leaning more heavily on the brakes in general, was starting to overheat the brakes on occasion (that issue would only get worse the more I learned to push). I noticed there was space for a little more tire upfront, plus the Forgestar wheels turned out to bend fairly easily, so I got some extra Apex wheels (18x8.5, ET35) and put 245/40 tires on them. They fit witout problem, but didn't leave much space for anything else. Honestly, I couldn't feel a significant change.
At this point, I'd already put a lot of track time (maybe 60 hours or so) on this car and more things were starting to show as consumables. Some definitely expected (like brake rotors, went with slotted 340x30 Stoptech, pretty good brake feel with them), some not so much. Especially studs. I was changing wheels frequently -- drive to the track on street tires, change there, then change back at the end of the day -- and had my first couple of stud failures around this time. Luckily, they happened when torquing wheels, and not on track (this time), so the only drama was drilling out the broken bits from the hubs. That still took a while -- I'd used heaps of red locktite when putting them on in the first time, and it didn't give out without a fight. Other than that, it was mostly going through more and more tires, brakes, fluids, windshields and learning how to push the car harder.