The Z31 Project - Race Car

[260DET]

Yeh I wish this suspension was as simple as the S30's, I made a couple of sets of adjustable S30 LCA's years ago but the Z31's has reference points in space which loses me. Have thought about doing a rear suspension transplant from a later model car but that would be too easy lol.

[PZG302]

Why make things hard for yourself if a later transplant works???

 

If an R or S chassis cradle bolts up why not use that?

 

Or look at a Z32 or Z33 bum to see if that's useful?

[260DET]

There are S chassis kits available but I like to try something with a bit of a challenge otherwise it's boring. Also with some fairly drastic modding it will be possible to get bump neg camber gain and maybe even a little bump/roll toe in gain, don't think that the Nissan multilink does that. Anyone got Susprog?

[260DET]

The less than $300 rotisserie works!!!!!  Check out that sturdy roof structure but it certainly needs the extra strength elsewhere that a well tagged roll cage will give, particularly above the door openings and down the A pillars.

 

 

[garvice]

Are you keeping the Targa removable panels Richard?

 

If not, why not weld in a sheet with a nice folded steel x to the bottom of it (similar structure to what is already there). Will look a bit neater than the shs you have there now.

[260DET]

Will be making a mould off the glass panels for structural fibreglass infills to be bonded in place. That will be done later, certainly after the cage has been done, no point in blocking off access prematurely. Wanted to get the bars you see in place to preserve some structural rigidity on the rotisserie.

[260DET]

Body work is progressing, most of the bracing previously mentioned has been done. The only major body structural job ahead is to make some transmission tunnel X bracing near the back, the front of the tunnel will be braced too in the form of a fancy transmission mount support later on. Car is ready for its cage once the bonded in windscreen is removed although it has no prospect of having wheels soon so transporting it is a problem. The rear semi trailing arm suspension is going to be heavily modified, to start with the original subframe has been deleted which necessitates a complete replacement diff mounting arrangement and that's just the start, oh dear.

 

Only one pic, which was taken last year. The two engine stand rotisserie works like a champ.

 

 

 

[260DET]

More progress, except for some transmission tunnel bracing and the roll cage the structural part of the job is pretty well done. The front chassis rails have been strengthened and braced back to the main body while the removable front suspension X member has been tied in with the front body X member. What with the engine and transmission and front suspension and steering all loading the removable member (four bolts to the rails) was something that needed work, when you look at any Z car up to the 31 they all lack beef in that area compared with modern cars. To finish the job a SST piece was welded in up front to counter any rail twist.

 

Hope that the pics show what I'm talking about, note that the car is on the rotisserie at about 90 degrees, front suspension bolt on bits are just in position and not bolted in.

 

 

 

[PZG302]

If you need a cradle for transporting the bare shell for a cage, the frames on castors I had on the S14 aren't being used now it is basically a roller. They should be pretty easy to modify if they don't bolt up to the available Z31 points.

 

I will be driving to Adelaide in early Feb, so can drop then off on the way through, or if you are in Brisbane before hand you are welcome to pick then up.

[260DET]

Thanks for the generous offer Matt, you will have a PM.

[260DET]

Onto the hard bit now, complete rear suspension revision where few (any?) have gone. The semi trailing arm setup is being converted to a trailing arm with lateral links system eg Gp C Bluebird, E36 BMW. The original sub frame is gone, the diff has been solidly mounted to the body, the inner legs have been cut off the suspension arms and two lateral links will run from the outer hub assemblies to a new rear diff mount setup. Lining everything up accurately and designing solutions are the tough bits, I'll let the pics do the progress talking.

 

 

 

 

[260DET]

More progress despite much heat in the shed, ventilation might be an idea. As far as I can estimate/measure the left trailing link rod end bearing is now correctly aligned and in place, finishing work to come after the right side one has been done. The idea is to do a reverse replicate of the left one, that will be 'interesting'.

 

Now to the two lateral links, need to do them next for the left side to make sure as far as possible that the trailing link is where it should be. Rotated pic from the rear shows a rough mock up of what will be involved, hub is on the far left, diff on the far right of the pic.

 

 

 

[260DET]

Pretty well worked out the applicable theory and the resulting fabrication to the extent that it can all be measured up to put it through the simulator. Pics show the lateral link adjustment options, the upper link length will be finalised once the simulator process is completed. Going to take my time with this, so far it's looking very promising but the devil is in the detail. The link shown in the pics is just a dummy, it's alignment is such that the rear roll centre should be somewhere around the 100mm target.

 

 

 

 

[d3c0y]

So much time... funny to see those CVs in their original home.

[260DET]

Hope this build is of interest to those who can't help themselves and have to modify car things, some of what is being done is applicable to S30's although S30 blokes seem more fixated on weight than body stiffness. Talking of weight, 1.5kg for the transmission tunnel brace pictured below.

 

 

[d3c0y]

I'm keen on doing chassis bracing on my car, however i'm kind of at the point where i'm in get it done mode. It seems like a waste to not do it now, while it's apart but I guess there is always room for future development.

 

There is a crossmember under there for the diff already, how much extra stiffness will this achieve and are you going to tie it into the rear diff mounts? Wouldnt it be more effective on the sides of the chassis rail and give you more ground clearence?

[260DET]

The heavy rubbish rear suspension X member is gone as part of the change in suspension type although stock it was soft mounted. Where the rear part of the new brace mounts there was a OE excuse for a brace so there were two M8 captive nuts each side which was handy, for the front two M6 captive nuts were drilled and tapped to M8.

 

Yes, I understand the urge to get yours on the tarmac, should be a real goer. One thing I guess that is going to be done with yours is to make a rear gearbox mount that acts as a brace there. With my FJ20 donked 260 I was able to fit a single SST brace across through the gearbox to engine gap, that's where a S30 badly needs bracing I reckon.

[260DET]

Everyone wants to know what's happening, too many Z31 fanboys, stop nagging 

 

Seriously, time has been spent running various rear suspension options through a simulator which is an interesting exercise in frustration and compromise. Because there are competing factors like roll camber on inside and outside wheels, roll centre and ride height. Plus the mundane matter of being able to fit the necessary fabrication in the space available without interference.

 

The result of all the various trial simulations is that the one selected provides that in roll, using a static -2.5* camber, outside camber will basically remain the same within the usual race car parameters ie camber gain will keep up with roll. Inside camber gains a bit much but that's part of the balancing act, roll centre varies from 170mm static down to 136 at the extreme roll figure of -5.8*. Which is good because the lower the roll centre the less chance of a jacking effect which can in extreme situations lead to a roll over but it may be a problem when it comes to settling on what to use at the front. It will at static have a lower roll centre, if under roll it does not keep up with the rear roll then it may result in front understeer. Which may not be a bad thing, a bit of initial oversteer to get turn in and some safety understeer when body roll starts to get a bit much.

 

Now it's back to fabrication oh joy oh joy.

Edited February 17, 2017 by 260DET

[d3c0y]

Come on rookie, you know we want pictures of these simulations. Words are so 1991.

[dat2kman]

No, i dont think there are all that many z31 boyfriends out there, dont seem to be many that are nagging, or was that gagging!

[260DET]

For the fanboys, including Jason, here we show The Chosen One What has to be done with the simulator is manually select each roll value and then note the changes. For this one 12 various roll values were input ranging from static to -5.8*, at that point negative camber had increased from 2.5 to 3.2* which is good, not that I'd want to roll that far to see what happened. In the usual range the camber stayed around 2.5. This rear suspension will have some dynamic toe in too and the trailing arm front pivot height has been adjusted to reduce the effect of anti squat.

 

 

[260DET]

Have a look at this video and see how the inside rear tyre in a corner unloads by going into more negative camber. Apparently this is a good thing for any rear drive car as it helps the outside tyre drive the car around a corner, I have heard of this before but never seen it so graphically demonstrated, nearly half the wide tyre is off the deck at times. So this qualifies what I said earlier about the project's chosen setup, gaining inside wheel negative camber is a good thing.

 

Edited February 18, 2017 by 260DET

[d3c0y]

Either way that is a fantastic video. I love it at the start where the camera basically goes inside the tailpipe of the car in front. How does one acquire this software so i can put my zed geometry through it just for fun?

 

I've never thought of the resultant effects of body roll in this way and is very interesting.

 

With my FJ20 donked 260 I was able to fit a single SST brace across through the gearbox to engine gap, that's where a S30 badly needs bracing I reckon.

 

Do you have a pick of this i'm not following.

Edited February 19, 2017 by d3c0y

[260DET]

Yeh it's a brilliant video, on the inside rear wheel thing I've also heard that negative camber in roll there causes the tyre to drag which acts as a brake on the inside wheel so helping the rear end to pivot round a corner. PM about the brace.

 

EDIT The simulator is here http://www.racingaspirations.com/ To get the full service requires a subscription of a few dollars per month, I'm going to cancel mine when it's finished with.

Edited February 20, 2017 by 260DET

[260DET]

doppelganger

Edited March 7, 2017 by 260DET