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Trailing arms are looking appealing, especially given that my chosen track width is so close to my engine/trans width, along with the body width requirements...
A cute issue I've already engineered myself into right there.
But I'm in for the challenge.

Mitsubishi used a trailing arm suspension on their 3KGT, and the AWS used bushing compliance as part of it's mode of action.
For the R33, Nissan used a lower a-arm and upper links, with the toe arms built into the spindles, again using bushing compliance to allow the steering angle adjustments.

Mitsubishi placed the hydraulic actuator in front of the wheels, connected close to where the trailing arms met the subframe, to maximize leverage.

Nissan put the actuators behind the wheels, with long extension links going to the toe links on the uprights. I think that was done to allow for less bump steer, but I can't be certain.

More thought is required for sure, probably over caffeinated beverages and pastries...

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Back in the '80s a lot of manufacturers went nuts for "compliance" and five or six links per corner. I read some of the SAE papers back in the day, but frankly all the doubletalk seemed to boil down to "we have created such an evil-handling car we had to add extra-super-duper understeer to the back end to keep our customers from killing themselves." And they'll usually toss in some "trailing throttle" and "roll steer" gobbledegook in to muddy things.

As to *how* they managed to build such evil handling in... I suspect much of it came from the half-dozen fist-sized rubber bushings they added for NVH, then tried to justify by calling it "compliance", then added all the linkery to try to keep each independent rear wheel from independently pointing any direction that would result in oversteer.

I'd love to play with a rear-wheel-steer setup "just because." But I don't see any justification for exotic multilink suspensions on a lightweight, high performance 7-ish car, though I'm open to enlightenment...

The reason I included AWS in my build requirements many moons ago is a bit foggy...
I think it was for decreased turn radius when in a parking lot, a bit more agility in the twisties, and for the sheer heck of it.

Now, because it's been on "the list" for so long, it's going to be done so I can trade any regrets that I would have if I didn't try to use it, for regrets that I actually did try using it.

I agree with the "bushings everywhere" ordeal, the 91 3KGT VR4 I'm working on has 16 bushings in the rear, counting the subframe/differential bushings.
There are four on the subframe, four on the diff, and four each per wheel, of which two are for the trailing arm.
I've spent more on bushings and adjuster bolts these past few weeks than I did on the engine for this project.

I think I'm going to tell MR NVH to go hit the road, and use heims/high misalignment ball bearings/roller bearings/ball joints in this cars suspension build.

Probably the only bushings I'll have are for motor mount/trans mount, since solid motor mounts will likely cause the engine to crack a dowel, or worse.

The engine will already have a little more BRAAAAAAAP than it should, since I replaced the exhaust port diffusers with aftermarket straight-through non restricting ones when I did the rebuild.

Since I started mingling here more, it's reaffirmed that my goals are possible, and I can someday get this project "done enough". I just need to coax out a few more known variables to narrow down the system of equations to something manageable, then start solving for the remaining unknowns.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Today I picked up a loaner rear iron at the rotary speed shop, so now it's go-time to get the adapter plate figured out.
I put my engine together before I bought my microscribe arm, so I wasn't able to easily digitize the bell housing pattern on a surface plate.
Trying to juggle the entire engine on the stand and merge partial scans from available angles introduced measurement errors, so I was sort of stuck for a bit.
Now that hurdle will be gone, and I can hopefully get some progress on the MDF adapter stand-in, and get the final clocking of the engine to trans right.

Then I'll have my final powertrain dimensions to start the rear subframe/suspension design.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

What transmission are you using, and where does the starter go?

The transmission is an Aichi MFA60 6 speed from a 2006 Nissan Sentra SE-R Spec V.
I swapped the 6th gear set out for a 0.54:1 set sourced from Renault, to tame things a bit for highway cruising.

The starter mounts on the transmission side, so clearance isn't an issue.


The angle makes it look like the filter pedestal is too close to the casting, but there's room with a factory Mazda filter and the factory filter adapter.

Here's another view, showing differential side and the exhaust ports.


Long before the engine was painted and assembled, I did a little "proof of concept" placement.





The jackshaft needs to go along side the exhaust, and things will be a bit tight, but I know it's doable.

As usual, click images for larger size.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

My HICAS rear rack came in on Saturday before work, didn't touch it till Sunday.

Earlier this morning (1:00 to 3:00) I digitized most of the pertinent features for the CAD model, so far it seems it will be rather simple to engineer it in. It's about 426mm long, and 21mm in diameter, except for the motor and gearbox in the middle. I'll hunt down the control module and yaw sensor later in the build.

I pulled more data off the borrowed rear iron while I was at it, so now I can refine the adapter plate a bit more. Hopefully I can use the free time from Thanksgiving to my advantage and get ahead on the MDF mockup.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

I think I'm about ready to scrap my current adapter plate CAD model and start over.

It's getting to be a mess, and I can't remember if it's the most up-to-date version of the patterns, or the proper rotation to clear everything.

I drilled the 1/4" MDF tonight with what I assumed is the correct adapter, and the engine pattern is good, so there's that small victory.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Why the ever-living @#%^$#@ did Mazda have to use fine thread metric for the engine bell housing bolts...

I can't find an M10-1.25 flat socket head cap screw at any supplier. I can only find custom orders for M10-1.25 button heads. And regular bolts won't work without notching the transmission, since I can't countersink the adapter where the engine dowels are.

I've been through this before on the adapter plate I made for the OM617/V5MT1 combo, and ended up having to make my own bolts.

Looks like I'm going to be going down that road again.

Good news is, I can use regular flange bolts going into the plate for most of the transmission holes, and I can get those in fine thread all day long.

Now that my whining is done...

Here's the 1/4" MDF mock adapter plate.


No hole in the center because I was too lazy to look for the jigsaw.

The loaner rear iron on the mock adapter.


Loaner rear iron sitting on top of the transmission, in roughly the right orientation, with CV axle inserted into the diff.


Had to remove the lower exhaust manifold studs from the housings on the assembled engine to clear the CV axle.


I set the paper printout that I used to drill the mock adapter onto the engine, with the dowel holes cut out, then positioned the trans on top like I did before, using the printout to get proper alignment.
No pics of that process because it was a bit of a challenge doing it, and it was slightly unstable. I'm glad I left everything but the differential out of the trans case for the time being.

For the first time, I saw confirmation that my CAD model is realistic.


(Ignore the issue with the rotor housing ports... Third party unfinished model...)


Another view.




I was holding the shaft up into the diff as far as it would go, since the bearing carrier hits the front cover. Already chipped the pant a few months back when doing a rough-fit, hence the towels wrapped around it.

Those two pics were a juggling act to get.

I'll have to make a custom header, and I'll never be able to use a factory turbo, but it's a weight off my shoulders knowing that the real world meets the CAD, and I didn't engineer myself into as much of a corner as I thought.

Now I just need to figure out the bolt situation, and I'll be good to go.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

After about 5 more hours, I've got things almost final.



Weight is around 7 pounds, so not too bad.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Forgot to mention, I ordered the starter bolts, transmission dowel pins, and the transmission end-case plug through Nissan on Sunday.

BOLT 23390-8H30A
DOWEL-BLOCK 30412-H1001
PLUG 31307-6J00C

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Spent some time with Matt doing random stuff in thw shop. Ended up working on the sump plate some more, which is being finished freehand, no CAD work, no solid models (till after), no printed templates.

Used some gasket maker to to transfer the front cover oil relief hole to the plate, then prick-punched for the center drill.


Jump cut to after the drill bits did their thing. I may open it up a bit more so I can fit a socket over.


Same thing for the scavenge ports.



The main pump pickup port was already drilled for a pilot hole.


And here it is back on the engine for another test fit.


Making a quick cover plate with a recessed pocket to go over the front relief valve.



Added some mounting holes that I can always zip off if I decide to weld it on instead.




More to come if I can get through work today.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Have you decided how you're going to do the rear suspension yet?

I'm waiting till the MDF stand-in for the engine/trans adapter plate is complete to decide on the suspension.

I did look at some Maxima/Altima/Sentra front knuckles today, as well as some other models. Nothing is really jumping out as feasible till I know if it will clear the engine/trans when they are mated together.

_________________
Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Are the bearings pressed into the uprights or do they use cartridge bearings?

The Gibbs IRS was designed by Martin Keenan to use Ford Sierra cartridge bearings bolted to relatively simple steel weldments.

I dithered for a long time over welding my own uprights, then figured that if the whole assembly was held to the car by a few welded tubing A-arms, why worry about building the uprights too?