As part of my plan to build for BSP AutoX, I'm planning on doing a multi-stage upgrade route focusing on slowly transforming from stock to a high degree of preparation.

I see that the KW clubsport suspension (probably goes for $4k) has 850lb/in springs in the front. If I were to try to duplicate their spring rates but buy Koni Sports and springs separately, I think I could get something near 90% of the KW's performance for 1/2 the price. The rears are 455 lb/in, so there's no worries there. It would also let me purchase the springs separately from the shocks, which may be desirable budget-wise.

So, the question is: can the Koni Sports provide sufficient damping for a 850lb/in spring?

 

No.

 

Thanks...

Are there any shocks that will handle this out of the box, or are custom valved jobs in my future?

 

You're going custom or at least a re-valving of an off-the-shelf shock. Have you done the math on those 850 lb. in. springs? What frequency are you shooting for with spring rate?

 

I was thinking about the springs from Nissan Motorsports, I think 500lb, with the konis. I talked to Koni and they said it would handle 500lb spring

 

No, make that a h*ll NO. And you need to be warned. Koni, if called will attempt to convince you that their shocks can handle far more spring then they can handle. I have extensively tested them and run them on the dyno. IMO they are good for about 450/450Anymore then that and your going to want a revalve.

Here's a setup along the lines your thinking that I ran that worked really well.
Koni sport shocks
Tein tapered spring 448lbs (reuses upper shock mounts)
custom lower spring seat (easy garage with a miter saw and a dremel out of 6061 plate)
427lbs oem rear spring on .5" cut down upper spring seat
bar setup, I would run either Hotchkis, H&R or a Cusco/Progress setup.

Honestly, you are better off not looking for a magic bullet with off the shelf parts. Go with something that someone has done truely excellent R&D on that specfic setup. I highly recommend Truechoice Phase III or IV shocks or entire coilover setup. Excellent R&D done by the Performance Nissan Grand Am team unitech. I ran the front shocks with rear koni yellows. Best performance I've ever had. Too bad the street ride was the worst I've ever had.

Another thought, Bilstein HD revalved by Bilstein to run Nissan Motorsport T2 springs, though honestly I'd ditch the rear springs that come with the kit and run either 427lbs rear springs with a heavely cut down rear seat or Cobb rear springs on a cut down rear seat.

And also, Anze Motorsports rebound adjustable Penske 8100 shocks $1800, valved for Nissan Motorsports T2 springs

Nissan Motorsports T2 springs 1" drop
Spring rates 690/690 (front springs known to not fit 100% like they should diameter wise)

Cobb Tuning 350Z Linear springs .75"/.9"
Spring rates 436/535 (as shown here http://g35driver.com/forums/brakes-s...new-parts.html )

 

Yes, when I spoke with Anze engineering, they told me their Penske shocks could be valved to whatever specs I wanted as part of the purchase price. However, IMO your intented use of the car does not remotely justify spring rates that high. Your far better off picking rates that shocks can handle, which happen to be more sensicle and testing, getting more seat time in the process.

 

WRONG, we've talked before. I tested mine with a lot of different rates, up to 560/500. 448/427 was more productive.

 

BTW, considering that I'm running a square, ie non-staggered, setup, how does that affect optimal spring rates?

Are Swift springs (custom) any good?

 

Yeah your right, been awhile.

 

check into tckline.

 

Their are better choices, I have shock dyno's on them. I would not own them. Not to mention that out of the box they have a disturbing amount of hysteresis (internal pressure imbalances). Valved for Nissan Motorsports T2 springs. Truechoice Phase III or IV are superior.