Autocrossing the Z31

[evildky]

So I'm considering keeping my Z31 and rebuilding it to be better in every way while bringing the budget total down and returning to the Grassroots Motorsports $2013 Challenge.

the car as it competed in the GRM $2007, $2008 and $2009 Challenges:
post4270042.html#p4270042

So when I built this car I stripped everything and made it pretty miserable on the street. No PS, no heat or a/c, most of the guages don't work, etc. This car was a composite of a $200 builder and a $450 donor, a $400 engine package, many parts were sold bringing the net budget down to about $50. Then I still had abotu $2000 to spend makign it perform and look good(ish).

The plan:
Mkke this car run, handle and look better for less money. How? Well, I picked up another donor, again with a bad motor but this one was a late 87 turbo 5 speed. This means I can have my CLSD hopefully working guages, beefier trans etc, and this car has already been zero'd out per the rules. I'm sanding allt he paint off, doing my own prep work and takign it to maaco or similar for a cheap coat of paint that will likely be better than I can do, or maybe I'll try my hand at it again, we'll see. The big issue is handeling, as the topic would dictate. I placed 4th int he raw sort last year in my MR2, as driven by me (which was 2 full seconds faster than the pro driver in the new Boss mustang Laguna Seca Redkey edition). This car has to be faster at an autocross, I want an FTD.

How do you make a Z31 out handle30 years of evolution?
This is where I'm looking for insight. Coil overs on a budget shouldn't be a problem, runing spring rates and ride height might be an issue. I'll definitely need to slot the rear crossmember to try and dial out some of the camber gain. I'm contemplating altering the subframes to raise their reletive height in the chassis. the rear shocks are obscenely long and one of the cars biggest issues that I can see, no one needs 10" of suspension travel unless you plan to ralleycross this car which I do not.

The questions:
Anyone ever use a shorter rear shock with any success?
Anyone ever raise the subframes reletive to the chassis to defeat some of the camber gain and bumpsteer issues wiht lowering the car?
Anyone ever move the engine back? (I was thinking of notching the firewall to gain some clearance to slide the bugger back a bit, stock weight distributions is good, could be a bit better)

Please, Chime in

[300ZXttZMAN]

Do you know how to weld?

[evildky]

lol, yeah I can weld, I can't imagine not being able to weld, it comes up more often than you might think

[300ZXttZMAN]

lol, yeah I can weld, I can't imagine not being able to weld, it comes up more often than you might think

SAME HERE!!!

If you haven't already done so weld up some supports and such in the car. Also weld plates to the bottom of the control arms to help stiffen them up quite a bit.

On my old rally truck (94 mazda b2300) I welded small plates to the bottoms of the control arms (they are stamped stamped steel so by welding them I closed the gap which made the suspension more predictable). So I suggest welding some small plates to the stamped steel suspension pieces if you have not already done so. (make sure you can still hit the bolts though)

I am going to be doing this same thing to my newly aquired s13 hatch when I start building it for drift.

[evildky]

the chassis isnt the problem, and neither is the control arms although I'm sure the fronts could benefit form soem stiffenting it's not an "A" arm, it's triangulated with TC rods, and the rear is a semitrailing arm with no stock adjustment and little room for improvement

my basic plan at this point:
find a shock to use in the rear that has way less travel and a much shorter rebound length
coil overs, probably gonna start out at 500 lb/in all around and tune from there
modify the rear subframe to allow for some toe and camber adjustment
fill the tc rod bushigns with urethane or replace with a spherical rod end
fill the rear subframe crossmember bushings with urethane

things I'm contemplating:
either relocate the inboard side of the frotn control arms up in the crossmember or possible sectioning the crossmember to allow it to mount higher in the chassis


modify the rear crossmember to raise it in relation to the chassis while keepign the diff in the stock location

[300ZXttZMAN]

Yea if you can get your center of gravity lower obviously that will help. Do you already have subframe spacers?

[evildky]

subframe spacers? guessing you aren't at all familar with the Z31 subframes. No they don't use spacers, the front subframe bolts direct to the frame rails, much like the Z32 but with a machperson strut more like the S13/S14 than the Z32 up front, and out back, well it's more similar to the 280zx or the 810 or the old rwd maxima's than anything newer. The subframe is basically a crossbar with a bend in in and a bushing at either end where it mounts to the chassis (this is similar to the bushingsin the z32 and so many other subframes) the center of the bend bolts to the pinsion end of the diff (long snout R200 allows this to happen) the diff then has a rear support/mount that goes up to the chassis. The trailing arms bolt to this crossmember and pivot at an angle from it, so when the rear suspension compresses or the car is lowered you gain negetive camber as well as toe in, this is why I want to raise the subframe in relation to the chassis, the chassis will be lower but the suspension will not be compressed adding unwanted camber and toe.

[300ZXttZMAN]

Ahh well Z32's are able to have sub frame spacers.

[300ZXttZMAN]

I am very unfamilar with the Z31's subframe.

[evildky]

what I'm guessing you care callign spacers are actually just locators, aluminum disks you slip in that basically lock the bushings in place. I'm planning on urethaning the bushings to stiffen them while not makeing the car miserable to drive on the street

[300ZXttZMAN]

Look here is what I am talking about:

https://specialtyz.com/shop/300zx/subframe-spacers.html

Does anyone make those for the Z31?

They really do work well for such a simple piece its a night and day difference. IMHO

[evildky]

yeah thats what i thought you were talking about, they limit the movement of the subframe and they actually lower the subframe away fomr the chassis a bit, kinda the opposite of what I want to do, if i move my subframe down I gain toe in and negetive camber and thats bad. I think in the case of the Z32 the biggest benefit comes form lowering the roll center and in the z32 the roll center is already much lower

[AZ-ZBum]

Don't you just love it when someone who has not a single clue about your car starts giving you advice about it? I sure do. It makes me all warm and fuzzy. /sarcasm.

idiots.

[evildky]

At least he was on topic and trying to be helpful.

With all your Z31 knowledge the only thing you bring to the conversation is disdain and comtempt?

[AZ-ZBum]

Okay fine... The only person I know who competitively autocrossed a Z31 did it bone stock. He said once you started modifying the car, you were put into a class where the Z31 could not ever be competitive. And this guy ran both an all stock Z31 and one of the first Z31s to run full coilovers. His modified NA was over 200hp at the rear wheels and he couldn't place well because of the SCCA rules. But in his stock Z31, he did much better in the points standings. He ran smaller wheels and tires as allowed by the rules and I believe he was able to change out the rear diff for a later 3.9 setup from a later model Z31. He also ran no rear sway bar and Gabriel shocks while running Illuminas in the front set on 4 (if I remember right). He used to go by the handle Pylon_Boy. His most recent handle on any of the Z31 boards is littlebunnyfoofoo. I could be a little off on the specifics of his car setup, but the overall gist of it still stands.

[evildky]

Thanks for adding to the conversation. Sam Strano drove an S130 turbo to a national championship in stock class, which is very similar to the Z31 so I can see it being competetive in stock but I'm more worried abotu raw time than fitting in any one class. Actually I'm thinking I can keep the car legal for SSM, and while I'm not really concerened wth what class ti fits it would be nice to stay out of XP or EM. The main issue is just how to make the car handle for little to no $. This might seem like a contradiction but it can be done, my street tire $2k MR2 1.5 swap is chasing fast fenderd time at local events, I want the Z31 to be as fast or faster.

[AZ-ZBum]

It's always going to be about personal preference and driving style. As I mentioned, he had the most success with a soft rear end and stiff front. Probably not to most people's liking. I would think this would make the car under steer a lot, but it really depends on whether you want to enter corners faster or exit faster.

No matter how you set up your suspension, I would really recommend a higher offset wheel setup. The car just feels so much more nimble than when they're pushed out to the edges. On a small track like autocross, it helps.

[pylon_boy]

Bum directed me here.


Here was my most successful solo setup:

G stock 85 n/a

Stock motor and drive train (I initially changed to a 3.9 for the modified class, but I changed back to the 3.7 to go back to stock class).

Stock suspension parts: Springs, rear sway bar, all new stock bushings, control arms, ect. new tie rod ends, steering bushings, ball joints, wheel bearings, ect.

Aftermarket suspension parts: Rear tokico illuminas set to 4 or 5 depending on the surface. Front Gabrial struts.
NisMo Front sway bar with poly centerbushing and end links.

Stock toe in rear (I don't remember what that was). 1/4" toe out front.

23" tall tires. This is hugely important. I don't know why, but it is. Someone who knows suspension geometry angles and all that math can figure it out. Whether it was 225/45/15's (Hoosiers) or 205/50/15's (Azenis) the car just came alive and "drove like an s2000... but slower"


I never got the highly modified one fully sorted out, but that wasn't because of the car. Also, that car was never meant to be competative either, just a fun experiment. It wasn't fun. It was so much more fun doing all the car setup and experimentation in stock class, then just being able to show up on race day and drive.

[evildky]

Thanks for the input, I too started out autocrossing an 85 n/a in stock class, a nismo front bar and new rear springs really changed the way that car handled, I was cometetive in our local classes (first DS then GS when it was reclassed). and I curently run SSM, as I'm sure you are aware SSM is just the updated name for the SM2 class, and these rules are pretty wide open. I'm guessing you're not running the Z31 in SSM/SM2?

so do you have any thought on ways to improve the cars performance withou class rules or limitations? I don't care if the cars ends up in EM or XP or SSM It just has to be competetive in the raw sort. Power I have figured out, I'm hoping to get closer to 350 whp. The biggest challenge is getting thecar to plant that power and still handle, The camber an toe gain with rear suspenson compression really limit the amount of power that can be planted on corner exit, and if I want to run for FTD I need to be able to plan that power. The CLSD can only do so much.

Thoghts?

[pylon_boy]

My goal when driving the z31 was to get it to plant the rear suspension as fast as possible. I didn't like rolling on the suspension and settling it slowly, since the toe/camber was changing all the way. I just wanted to get the rear to where it was going to settle as fast as I could so I could concentrate on throttle input. Back when I was competitively racing, my autocross setup was more aggressive that other people's z31 drift setup.

When I had my stupid modified n/a it was in sm2. I never was able to take that car to a test and tune session, but I just didn't like how the rear end of the car slid around. I ran a staggered tire/wheel setup (the previous owner did the engine, fender flares, and wheel selection) which was 17x8.5 front and 17x9.5 rear. I chose 245/45 for the front and 255/40 original victoracers due to budget constraints. 275's would have been a very tight fit and I wasn't totally sure they would have fit. If I could go back I would actually just get some wide 15x8 or 8.5 wheels and stretch some 225/45/15 hoosiers across them (they had a 9" section width back in the day).


Looking up their current data (http://www.hoosiertire.com/rrtire.htm), those tires still have the same tread section. However, they also have a 275/35/15 tire available in autocross compound (however, the tread section is only 1.1 inches bigger) and you get that awesome 23" tire height.

Not that you have a limitless budget, but that's where I'd start.