Thanks for your observations FieroWannaBe.

For Fieroguru: Earlier on, I did look at making the cradle wider, and shortening and moving the inboard lateral link mounts outboard and upwards, although only superficially. I quickly realized that the F40 overhangs the forward inboard lateral link mount by way too much to ever make enough room for it vertically. The other problem with shortening the lateral links is that it would only exacerbate the angle of the links with respect to the ground, worsening the roll center movement.

One of the things I did to get a warm fuzzy feeling about whether an SLA set up like Datsun1973's might fit, was to overlay the scale drawings of my front control arms onto the rear suspension. My logic here was that since the front geometry works so well, if it could be replicated in the rea, then the rear roll center could potentially be tamed equally well. Here's my first crude attempt to see how the front geometry (in red) would look if it were moved to the rear:



I simply cut and pasted the two front control arms in the exact same orientation they are to each other from my final front suspension configuration, onto the rear Stage 3B rear modification drawing. Even though I don't intend to replace the rear lower lateral links with a control arm, for this exercise, used the front lower control arm simply to locate where the upper rear control would lie. I aligned the front lower control so that the lower ball joint was in line vertically with the hole in the rear knuckle for the lateral links and the inboard pivot was at the same height as the lateral link mounts. The upper control arm then just fell into place.

My first observations are that:

1. the geometry can't be exactly the same as the front since the lateral links are shorter than the lower control arm, and the upper ball joint does not fall conveniently where Datsun1973 has located his upper joint on the knuckle;

2. since the lower lateral links will be shorter, the upper control arm will likely need to be proportionally shorter as well, which will make it easier to package within the available space;

3. the lower frame rail appears to be well located to support the upper control arm pivot, or at least a new structure to support the pivot;

4. with a pushrod set up and shock orientation like Datsun1973's, the strut towers become redundant and could be replaced by a simpler and less intrusive structure tying the upper and lower frame rails together and making more room for the Northstar rear valve cover (not to mention the dead give away the strut towers provide to the actual lineage of the car when the decklid is open.);

The next thing I want to do is draw the rear lower frame rail to see how the front suspension geometry fits in the side and top views... more soon.

Edit: Updated drawing

[This message has been edited by Bloozberry (edited 09-09-2012).]

Blooze, from the pics 3-4 pages back...you are going to change the front ball joints and tie-tod right??

I suspect you just assembled the parts for an example mock-up...

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. All original.

I see I have some catching up to do on feedback:

For Fieroguru: You may have a good point, but I'm not sure yet that I'll have to relocate the lateral link attachment at the upright like you suggest. Even if both control arms would need to be angled upwards at ride height as my initial sketch shows, it shouldn't matter much if I can duplicate the control of roll center movement achieved in the front suspension. What I mean is that in the front, no matter what the control arm angles are at, the roll center stays roughly stationary. The challenge will be to define the coordinates of the control arms that not only control the roll center though, but also the camber and toe, given different packaging constraints than the front.

Fierogt28: Good eye. I do have new tie rod ends to install, they're just not painted yet. The lower ball joints are new, but the uppers aren't. They're actually not worn out, but they do detract from the rest of the new parts dont' they? Now that you've pointed that out to the whole world, I feel like I have to get new ones... thanks alot.

exoticse: Thanks for the compliments... it takes an experienced eye to see the potential in a kit car at this stage.

Austrian Import: I would take you up on your offer since the more brainstorming there is, the more likely the best solution will come to the surface. As you likely know though, posting pictures is easy. What takes time is explaining them... more than I can afford at this very early stage. Perhaps once I'm out of the preliminary concept stage I'll have more time. Feel free to download my images from here and repost the ones you think will generate discussion over in your thread though. I always check out new posts in there... afterall, Datsun1973's contribution comes from your thread.

Edit to add: thanks too 355Spider!

Now back to the latest update: It's taken a considerable amount of effort to map out that rear lower frame rail, especially since not all of it is easily accessible for measuring. As usual, I head out to the shop, take a whole slew of measurements and make a hundred little sketches, come back to the office and try to make everything fit. The computer is amazing at simultaneously showing how accurate something can be and at how terrible I am at measuring things. It's no wonder you hear that saying "Measure twice, cut once" so often among people who work with their hands. If I'm lucky, I'll only have a few discrepancies to iron out... wasn't the case this time around. So as one PFF'er states in his signature, "you get what you pay for", consider how much you paid for these drawings before building a new Fiero using these as blueprints!

For now though, just to show that I AM working at it, here are the top and side views of the stretched frame and raised cradle. For the eagle-eyed among you who are curious why I indexed the longitudinal axis in both drawings where I did, well, it's a long story but it boils down to using the rear trunk wall as the index point since it was the closest repeatable measuring point for all other points on the frame rail... and it was the easiest point of reference to use while sitting in the empty engine bay.

I'll superimpose the front suspension geometry over top of them in my next post:

[This message has been edited by Bloozberry (edited 09-07-2012).]