Thanks for the insight. I have had my 2003 350Z suspension for over 6 months now. The performance is definitley better than the sedan sport suspension but as you said the bounce and porpoising is present. It doesn't bother me as much as a lot of 350Z owners profess but I guess I just got used to it and took it for what it's worth, a suspension designed for a sports car. D-specs will definitely be my next move while keeping the 350Z springs. Especially when the D-specs can be had for quite a good price on ebay.

 

Why not keep the Sedan stock struts on with the Z springs? Switch them to dspecs after the stock ones blow?

 

Nothing to do with wear. Everything to do with control. Which the D-spec shocks will be vastly superior at. I tested the Z springs with sedan sport shocks at the bequest of several members. While the ride quality was much improved. At the limit behavior was downright scary, especially when a bump or just a mild undulation was encountered while pulling even mild G's. Also all the old sport shock bad habbit's came back, noise dive's when you hit the brakes, back end squates then your on and off the gas, and the car was not as willing to change dirrection's. Poor weight transfer management. I went back to my oem Z shocks in a hurry, but not before I tried the combo below.

What did work with the oem sport shocks was Z springs in the front and oem sedan springs in the back with cut down upper spring seats, resulting in a 1" front drop and 3/4" rear drop. Weight transfer performance is still poor however.