Once you start changing parts on the car, you are bumped into a "higher" class. "Stock" classes would be considered the lowest class, then Street Touring 2, then Street Prepared, Prepared, and finally Modified. I run in Street Modified 2.
I did my modifications in gradual steps, not being able to afford very much on account of making poor money at a job I was way overqualified for. The first steps were what was legal within stock class. First I changed the front swaybar to a larger 26MM NisMo unit. I put in Tokico HP shocks and was satisfied for a while, then I decided to get out of stock class and replaced the springs (Eibach), then replaced the springs with stiffer springs (yes, I was redundant). The springs from the SS model 300ZX (only of which 1000 were made in 1988) are the stiffest stock ride height springs you can buy, so I bought them when I found a set. Then I found late model (Z32 style) tension rods and longer front control arms. The new tension rods made a big change, especially after I installed the polyurathane bushings. The poly bushings made a HUGE difference on race tires. I can't even put into words how much more responsive and crisp the car feels. I have a spare set of stock rims for race tires. I painted them because they were so ugly, now they actually look pretty good, if not better than the plain aluminum.
Here they are in the car while loading up for an event in another state. Some of you may notice that my car is a 2+2 (meaning it has 4 seats). How many people with 2-seaters can fit 4 wheels and tires, a floor jack, a 5 gal. air tank, a tent, two helmets, two coolers, luggage for 2 days and ANOTHER PERSON in their car? NONE, HA!
Side note: The 2+2 is superior to the 2 seat model in many aspects. I have both 2 seat and 2+2's so I can easily tell the difference. 2+2's ride better, are more forgiving when you get them out of shape, have slightly less tendency to over-steer to begin with and you can cram 3 of your friends into one and not get pulled over because of it. On top of that, all top level Z31 race cars were 2+2's and most Z31's made for Europe were 2+2's. Just because the only 2+2 turbo to come to North America came with an automatic transmission does NOT mean it performs worse on account of being a 2+2. Also, some people decide to bring up the issue of weight. 84-85 model 2+2 Z31's weigh less than ANY 86-89 model; enough said.
The stainless brake lines were a nice addition, they gave a more firm pedal and better feel for the lockup point. The Axxis Metalmaster pads made a nice difference in stopping power as well, however they seem to work much better once heated up after a fast stop or two. Here is a nice picture:
Then I wanted more power and did the turbo conversion.
Of course, little did I know the road I was taking. I kept wanting more and more from the car, as it kept delivering more for every incremental modification. I still believe the Z31 is a completely untapped platform that is capable of much more than people give it credit for. This is when I finally upgraded to some lightweight 17x8" wheels and 245-40-17 rubber. The sticky Kumho ecsta MX rubber was just the ticket to make me want to tweak the suspension even more. I bought some old stock Koni swaybars from a place online; they offer the highest rates of any of the aftermarket bars but are long discontinued. I eventually decided that coilovers were the only way to go, and after some deliberation and research, I installed Tenabe coilovers made for the S13 240ZX.
blah blah blah it never ends!