Hello.

question :

I have been taking my 2008 350z to vir and really enjoying this car.

At the kink on the front straight the car seems to hop and lose grip at 100 mph +, -

instructor said to check the alignment.

What alignment issue would cause this ?

car is lowered with stein shocks and springs by PO.

running 245 40 18 front , rear 275 40 18.

Yokohama advan apex 280 TW.

also , looking for an effective rear spoiler or duck bill. Any recommendations?

thanks
NBF

 

Welcome- your first post is better placed in the motorsports section where Z racers with VIR experience can comment.

 

That takes me back like 5 years to when I was trying to figure out my suspension setup. I had a couple session where the car actually got sideways at the front straight kink at 120 mph. Not fun. In my case it was because I gutted the car, went to a square 275/35/18 setup all around but didn't adjust the suspension for the increased front grip. In the end the problem is the same, your rear end is not gripping as well as the front. This could be down to a myriad of factors, but since you don't mention issues in other corners my guess is this is not bad alignment or worn suspension bits. Likely your setup is too stiff in the rear, which will definitely show up in the front kink.

In general I would start by softening the rear sway bar or if you're running oem sway bar, just disconnect it altogether. If you have adjustable sway bars you can try stiffening the front sway instead. I don't even run a rear sway bar at all, but again that's my setup.

If that's not enough, your rear spring rates might be too high. These cars have front weight bias, especially when you start gutting the car the rear gets very light very quickly and the spring rates have to compensate for that. Despite popular opinion stiffer suspension is not necessarily better.

One more thought, how low is your car? If it's too low you might no longer be getting full travel from your shocks, so you're basically bouncing off the stops causing all kinds of traction issues.

As far as the rear spoiler goes, I ran a duck tail spoiler for a while and I didn't see a major improvement from it. Really no low mounted spoiler will provide that much downforce, to see a real difference you'll need a wing mounted high enough to be in clear air, which means at least a foot off the rear lid.

 

Dr. Hoon

thank you for the tip on the rear sway bar I will check that out.

I have enjoyed your track car thread on this site.

NBF

 

How impactful is a rear-mounted (1ft above the decklid) spoiler on these cars?

 

Are you asking about a wing or a spoiler? My 9 lives wing has been transformative to the performance of the car, especially at high speeds tracks like VIR. Going thru uphill esses I can maintain 125 mph whereas before I was washing out at like 110. Worth easily a couple seconds a lap if not more.
A good quality well designed wing is worth the investment. My first carbon wing that came with the street faction mount was a joke. The 9 lives wing is aluminum, light, adjustable and low drag. I only run it at like 5 degrees aoa, that's plenty.

 

Wing - all apologizes

Just curious - What didnt you like about this setup?

 

If you go back thru my posts at the time, the first cf wing that came with the mount actually started to come apart at the seams first time I took it out at VIR. Now, to give credit to Street Faction, they did send me a replacement wing that looked better made, but I never used it. There was no adjustment on the CF wing and the AoA was way too high, so in the meantime I got the 9 Lives wing that's properly adjustable and I've been running that ever since. Also, just looking at the CF wing it was obvious it was made for looks not for aerodynamics, the profile was not a proper airfoil at all. But the actual crash bar wing mount is of good quality and I still use it. I had to reinforce where it mounts to the trunk walls, but beyond that I'm happy with that piece.

Pic of wing cracking apart...


Difference in shape and AoA

 

what are your front and rear toe settings? improper rear toe can make the car feel very squirrely and unstable above 80mph in long sweeping turns.

 

Thank you for the replies.

I will take a look at the front / rear toe.

can I measure this with a tape line , or should I take it to an alignment shop?

any tips for getting an accurate measurement ?

I measure from front of wheel to front of wheel , and then rear to rear ?

thanks for the info about the 9 lives spoiler.

would the Z1 front / rear sway bars be a good thing to look into ?

 

Z1 sells toe plates that make such measurements much easier. Right now they are on sale

https://www.z1motorsports.com/all-cy...s-p-41720.html

Adjustable front sway bar is always a good idea. Rear might or might not be beneficial depending on your setup, spring rates, etc.

 

An update :

I had new rear bearings installed that helped immensely in the kink where I had a previous very unsteady feeling.

new aluminum diff bushings have recently been installed.

Along with z1 aluminum collars for the sub frame bushings.

car feel is much improved, I am getting a grinding / clanking sound from driver side rear.

I am planning to install rear axle shafts.

there is a contact with the new sway bar and the aftermarket invidia exhaust from PO.

I could see the red paint on the exhaust on passenger side.

any recommendations for a fix ?

could that be the source of the noise?

it sounds like the noise is getting more pronounced / more frequent but car driving feels unaffected.

Noise mainly was at slow speeds or at deceleration. Noisier in lower gear. Would generally stop when clutch is in.

thank you. Great forum.

nbf

 

So regarding the noise, there is a big difference between clunking and grinding. Clunking I would definitely attribute to some parts of the car moving around and coming in contact, be it your exhaust and sway bar or something else. Grinding implies rubbing on something that's rotating. Since you're saying the noise stops with the clutch in, this could be the throwout bearing or the transmission itself, but if you mean it goes away when clutch is engaged and car is stopped the list expands to your driveshaft joints, the differential, the axles and cv joints, etc. Does the noise go away if you engage the clutch when the car is moving?

 

The noise is only present if the car is moving.

it does seem timed to wheel speed.

I bought two replacement rear axles. (119k miles on the car )

It seems to be coming from driver side rear.

Maybe be the cv joint closest to the wheel?

hopefully the axles will be installed very soon , and that will clear the issue.

either case I will report on the result.

thank you for your reply.

nbf.

 

pick up the car and shake the wheel with both hands vertically and horizontally, see if there's any play. Also rotate the wheel by hand and see if there's any unusual noise. Could be wheel bearings not axles...

 

Rear axles were replaced and that fixed the noise.

the boots were intact , but cv joint closest to driver side wheel was cooked.

Car did great yesterday.

solid diff bushings really help improve the feel and responsiveness. I Highly recommend that upgrade.

next on the list is a half cage with seats / harnesses.

really appreciate the info and great responses on this forum.

It would be fun if some of us could organize a spec z event in VA….

 

yea we need to get an event planned at VIR and run some Z's!

 

I probably won't be back to vir until November