03threefiftyz

My opinion (BSP car),

For silky smooth concrete you can run a pretty high natural frequency (close to 3hz on a dedicated SP or higher Z car). If you run on asphalt (less grip) or several sites with bumps, you will need to compromise. Even Lincoln would be too bumpy for that level of spring. As far as split, you will have to look at your existing corner weights. In street prepared we can get much more weight off the back of the car than the front. My car is a no compromise, full prep car and has a W/D of 56/44. I don't have the motion ratios for a 370z, but if they are anything like the 350z you will need to run a fair amount of spring. You really have to decide a few things....surface conditions you plan to run, tire size, what size bars (if any...particularly in the rear), whether you plan to have aero, and car weight.

Given the the current W/D and now that the car has aero...I tend to run about even frequencies on the front and rear. Less hz means better mechanical grip (to a point) and better on bumps....just to generalize. More hz means more transition friendly. The 03 350z comes from the factory with ~1.25hz on the front and ~1.3 rear. On the polar opposite, formula cars run in the 4-5hz range.

If you plan to run in street prepared, you must retain the OEM layout in the rear as going to coilover changes geometry and motion ratio (this part significantly).

As it sits, my 2920lb BSP car runs at 2.34hz front and 2.31hz rear on 900/750 springs and OTS Motons up front and custom rear. I run the front hotchkis bar at 3/4 stiffness (surface/grip dependent) and don't use a rear bar. Those frequencies may have to be raised depending on how the car shakes down in testing after the aero and wider wheels....particularly on concrete.

Calculating the frequency is pretty easy... it is 3.13*sqrt(wheel rate/sprung weight).