I ran this weekend on the stock tires, stock alignment, no mods.
I spun my first run. The Sport-Plus or Sport setting for the e-gas are useless. There is no purpose for these things. Gas response is non-linear, at high RPM (as I was through a transition) makes the car dangerous. I slightly hit the gas on turn exit, and the car just lost the rear grip, like and on/off switch when I just needed 20% gas.
Hot tire pressures 36 psi front/rear. I did two runs at 40F/36R but the car felt better and faster on 36/36. This is consistent with my tire pressures on Michelin PS2 and my GT3.
Suspension in Sport mode has a predictable feeling. This car doesn't understeer as the E46 M3 (which awfully understeers). Very well balanced car, and very fast, it feels lighter than it's. I was really impressed with the M-diff, the finish was a fast right sweeper (60 mph), at full gas the car started to get away progressively, but not losing control.
My fastest time was 1.9 secs behind a two time A-Stock National Champion with his Vette on race tires.
I know from experience how much faster are the Michlin Pilot Sport Cups against the Michelin PS street tires, but for autocross you can get even faster tires (A6/V710).
I think that this car will go to Super Stock and not A-Stock. In A-Stock it would be very competitive. I can easily drop over 2 secs just by switching to 275/35R18 A6. This would already put me as the fastest stock car at the event, and a few tenths behind the BSP and CSP National Champions (they were at the event).
Then add car preparation (alignment, light wheels, muffler delete, a 6-speed manual no option car) and the car would be even faster.
03 Celica GTS
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07 Cayman S
08 BMW M3