Ok, sorry to all if this turns out to be long and involved. But I believe in telling all the good and any bad in reviewing. No sugar coating.
Theirs no reason why my findings can't be weighed by coupe owners.
A good question is why would anyone want to do this? Any one that drove the Z and loved it's firmer more sport oriented suspension, it spite of any perceived ride harshness. I do not mind a firmer suspension that delivers the handling goods. And this would be done by someone that doesn't want to spend $1400 on coilovers (least not yet) and doesn't need the adjustability. Add to that the fact that no one make performance struts for the car, yet. This would also be done by someone that does not want the compromise progressive springs have on ultimate handling and behavior. The car has linear springs for a reason.
One other reason, the Z springs are shorter and you'll lower your car about as much as prokits. I'll show you a picture of my car with the setup so you can judge the lowering. They lower the car 7/8" front and 1 1/8" in the rear.
The bad: Let's get this out of the way, front and center. Ride quality is the most serious compromise in doing this swap. The ride is no different than how the Z rides. Off of main roads and at lower speed the sensation is, that the suspension greets bumps with allot of reluctance. Just like Gordon from koni said, they dialed in a little do much compression dampening to get really good turn in performance. Add to this the spring action in the seats and you get a bouncing sensation on certain bumpy roads. The car does exhibit some freeway hop on concrete freeways that have expansion joint's built into them. In describing all this, it is not as bad as when I have made the mistake of running weak struts on a lowered suspension, that's worse than this. I may decide to improve the harshness control with Koni sport struts coming out this fall. In any event, theirs allot of Z owners that have really spoken up about the perceived bounce issue and ride harshness. Many of them have replaced their springs with eibach's progressive spirngs, to cure the issues. This makes for the chance to get excellent pricing on used 350Z springs and struts, I got mine for $150 shipped.
Let me bring to the table the things I do not like with the sport suspension (coupe runs the same suspension as the sport suspended sedan btw.) And then we'll get into how these problems are fixed.
1. Excess weight transfer during hard brake applications. Do a hard brake application and the suspension gets to nervous and unsettled, like it's really not sure of itself. Also their's WAY to much weight transferring going on when getting on and off the throttle. This also is a bad thing if you need to do a gear change mid corner while carrying a g load, such a weight transfer can upset the car.
2.Poor at the limit behavior with VDC off if you make a mistake. If you reach the adhesion limit and don't touch the throttle the car will corner in a excellent neutral balance however. Cornering loads have to be lighter than normal to be able to start applying power down. It's far to easy to spin the inside wheel with the open diff.
3. Turn in performance is lacking, the car isn't willing to change directions like it should.
So, how do the 350Z springs and struts work at fixing the above issues.
1. Weight transfer is almost eliminated. As a result the car is dramatically more steady and sure of itself when doing hard brake applications, night and day better.
2. At the limit behavior is also greatly improved. The car's neutral balance is maintained. But now I have the ability to steer the car with the throttle, without fear of sudden oversteer. Also the window in which you can start to apply power in corners and not spin the inside tire is much better now. Enough that I'm not dying for a LSD. (I still need one, don't get me wrong).
3. Turn in performance is now on the side of WOW! Flick the steering wheel and the car instantly obey's with out delay. Initial bite is also much higher.
Some technical highlights:
With the springs off the car and the fact that I own another set of Z springs I invested in a dial caliper and had a engineer I know work the math to give me the spring rates for the 350Z, G35coupe and G35 sedan with sport suspension
350Z: 347/419 front/rear
G35 coupe & sedan w/sport susp: 357/407 front/rear
Also I took the same dial caliper and measured my stock sway bar diameter. Then I crawled under a 350Z at the local dealer. I had a hunch that they'd be the same size between them and I was right. 33mm front and 20mm rear
Here's the pic of my car to see how the Z setup lowers a G35 slightly. I tweaked the pic to show the wheel well gap better. Unfortunately, the pic is over bright now. (forgive me in the linking doesn't work).
Ivry 6mt sed
Injen CAI, 22" resonator
8X18 Enkei RPM2 45mm
Kumho MX 245/40
<P ID="edit"><FONT class="small"><EM>Edited by merlin on 07/12/03 10:04 AM.</EM></FONT></P>