Looking for some experienced road racers to chime in here... I have my 350 sitting on Pss10's lowered about 2". All sway/strut bars are stock and I just recently upgraded to a Quaife with 4.10 gears. The issue I am having is snap oversteer. I find that I can break the rear end loose quite easily (easier than you'd expect). Now before you start asking if its not the 4.10 thats causing this change in perception, let me give you some background on my driving history. I have participated in over 20 track days and have done a few drivers education schools in which I was able to drive a s2000, lotus exige, subaru wrx, spec miata in rain/snow/dry conditions. All of these vehicles felt better balanced than my Z does. I just dont feel confidence from the Z.
Ive commandeered a set of scales and through my car on them tonight. I have attached the printout to this post. The first printout is the car and the second is with me in the drivers seat. As you can see I have 51% left hand balance and 47.5% rear balance which im pretty happy with, however im working with a reverse wedge situation (46%) which will cause the car to understeer in right hand turns. Now ive read that you want your wedge to be within 1% so i know there is room for improvement there and I will try to dial the car in tomorrow night.
Do you think that balance of the vehicle is whats causing my issues or do i need more fine tuning in the rebound settings, different sways, different tires/tire pressure, or perhaps something I havent thought of? Any advice is appreciated.

P.S. running stock camber/toe settings.

 

here's to hopping scotts300 and terrasmak will chime in...

just a quick question though.. did you make sure there was no tension on or disconnect they sway bar endlinks were before you scaled it? Also adjustable or stock links? and any bushing upgrades?

i have always made sure that they way the car is driven the most (3/4 tank of fuel, driver weight with normal gear) there is no pre-load on the bars. always the first thing i used to check when scaling my dads circle track car

If you read through the Motorsport forum you might be able to find some old threads... this one has some info

https://my350z.com/forum/brakes-and-...er-weight.html

but sub'd either way

i'm in the same boat though.. will be able to install the rest of my suspension in a few weeks and then will have to figure out mine as well.. but step one for me is get an alignment and then get corner weighted after the springs settle... then double check alignment

 

Also tire pressure has some small influence as well... so get that set to your hot pressures or in the middle..

 

Good luck with the install. Are you going full coilover or still sticking with strut/spring in the rear? The install is fairly simple, dialing it in is whats taken me some time. I wouldnt get the alignment done immediately. Id drive it a few miles, let it sit for a day or two to sag the springs and then drive it over to the alignment shop... Did you get the front upper control arms and and rear camber arms? If not you will not be able to get it back into spec.
I made sure the tire pressure is where I want it, however i didnt disconect the sway!!! I completely forgot to do it Ill retake my measurements when i return home today but I dont forsee too much change since its static weight on a level surface. Ill keep you posted. Thanks

 

You have the same problems all of us have in road racing the Z33. That LF-RR diagonal is always heavy and the RF-LR combo is light. Even with coilovers, there's only so much weight you can jack without screwing up some other component of the suspension setup. The first step in suspension tuning is to go with the tools that will make the biggest adjustment difference and in your case it would be adjustable swaybars.

While swaybars are a coarse tuning device, they'd be the first thing to pursue if you're looking for bang-for-the-buck improvement. I'm a bit mystified by your description of "snap oversteer", which is not something that is a common complaint in the Z33 (particularly with stock suspension). Does this happen with every corner? Is it only on corner exit, or are you losing the rear end before the apex of the turn? Did this happen before you installed the Quaife?

 

Without diving into all the things you can adjust, first and foremost you need to convert the progressive PSS rear spring to a 2.5id linear spring. All you need are the springs (eibach/swift/hyperco) and a set of lower perches (BC racing has the parts available just call them).

On-limit predictability is exactly what this mod will completely transform. After I converted my Bilsteins it brought a level of predictability and confidence that was not there before.

Aside from that, you could lower the rear (decrease rake), and provide your damper settings, exact ride heights, and tire pressures to help us see if there is anything out of the ordinary.

 

Thanks for all the advice guys. Glad to hear that I didnt butcher my install/ initial setting. I will try all the suggestions and check back in soon!

 

Did you realign the car after dropping it 2 inches?

 

Haha of course I did!!! Not getting an alignment after any type of suspension work is just silly

 

Seen as your dropped 2 inches i'm guessing you have adjustable links. and you're right they should be set with zero preload when static... however, just my experience, i set them to zero pre-load with driver in car. Also make sure they are still the right length, sway bar ends should be horizontal with the end-links as close to vertical as possible but that once again doesn't effect static load

Also did you change the drag link for adjusting "toe"? nothing to affect static measurements outside of toe/camber (but incorrectly) but it will mess up your bump steer

Yeah, I went full coil, I've had adjustable arms F&R already for some time, just have the mid links sitting on a shelf waiting for my coils to be built. I went with AMR for mine. I'm only stateside for 3 weeks and have so many other things to do, so i'll only have time be able to get them installed and the car back to storage, so it'll have a month to settle out. that's the one bad aspect of oil field jobs... not enough time to see start and finish of some things in the same month

 

an oldy but a goody..

https://350zmotorsports.wordpress.co...-spring-rates/

 

The direction I will go is, the car is way low for a progressive spring. As we all know a progressive spring is soft and gets stiffer as it compresses. Being lowered two inches it will be soft will it hits the bump stops. You hit the bumpstop hard, break traction, suspension unloads and now you have a snap oversteer situation.

Raise the car up a bit, swap springs to linear.

Btw, what diff, tires, sways , camber settings are you running

 

Honestly, I would assume you can get that cross balance a bit closer, but T-smak is likely on target... too low and bouncing off the bump stops (instant oversteer).

 

Sorry for abandoning this thread for a bit... Id like to bring this back. I will re-weigh the car and like to take height measurements and post them to give you guys an idea of what im working with... ive gutted the car drastically... thinking the car will be about 300lbs lighter, but i will get some weight back with the weld in cage ill be putting in. Anywho, I have a few questions:

1) Linear springs for the rear were suggested... what spring rate would be appropriate to match the 370lb fronts? Also what length of spring should I be looking for? Any suggestion or product links would be appreciated.

2) Measuring height: What is the standard for measuring height? Floor to top of wheel arch? Anyone have stock height figures? I know I saw them in a FSM somewhere before.

Thanks in advance!!!

 

Found the stock height in relation to the fenders, will post figures tonight.

 

Replied to your PM but figured Id post here also...

You want a 7" or 8" spring, assuming you keep the rate around 400-450lbs/in. I used a 200mm (7.87") 450lbs/in (8kg/mm) spring (Swift) to match the stock Bilstein fronts. I initially used a 6" 400lbs/in (Eibach Elite Series) with a Hyperco CS100 helper spring and it was way too low in the maxed position. With the 200m 8kg.mm spring you will be able to get the ride height where you want (adequate piston travel, lower than stock obviously) and the handling is great. You'll be fine with either a 400 or 450lbs/in rate, which is what I would recommend to match the stock Bilstein fronts and not have to revalve the dampers.

And to save you some headache, if you go with a helper, the Eibach spacer model "SPACER250" is the one you want, it is thin and has the proper ID to allow things to work properly. I tried the Hyperco 18DS100 spring divider and it doesnt work for our application.

Hope this helps.

 

I would probably start with a 450 lb rear spring. I would actually ditch the front spring to something stiffer too.

 

Guitman, thanks for the advice but I think there is a small misunderstanding. When I orchard my pss10 kit it was coilovers in front and spring strut so in rear, utilizing the stock spring bucket... I will look for a spring that will work in the bucket, if anyone had info on ideal length it would be appreciated, but I'm guessing it'll be sane sputtering rate. I may just pull the bilstien spring and measure it.

Terrasmak, thanks for advice as well. I think I'll keep front springs for now to avoid excessive understeer, if the rear spring change doesn't do the trick I'll see how it feels.

Measured the car last night, keep in mind this is after drastic gutting... the front is dropped 1.15" and the rear is dropped 1.2". Clearly my menory doesn't serve me well as I said 2"... fail... I will search for those rear springs, if anyone wants to share their setup or any other info/insight it'd b appreciated
Have a great day guys!!

 

No misunderstanding, to make a straight 2.5id spring to work you meed to get a lower bucket adapter, such as the one sold by BC racing. It sits in your lower spring bucket.

 

Piece in the lower right of this pic: