What is the best suspension for improve handling and lap times?

AlWakRa

First, seat time, as 370z is well balanced car from factory.

Then, you should look into upgrading your brakes to not face any brake fade.

As suspension, you would start with alignment kit, like OptionZero suggested, with FUCA and RCL, getting more camber and better tires, you would improve your car a lot. Changing the LSD would also improve the car predictability and exit speed.

You can get swaybars next.

Those would bring the best out of the car, as the stock suspension is well balanced.

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