Possible Suspension Conversion. Serious Tech Discussed

[mranlet]

As some of you may know, my BG Wagon is RWD with an R200 differential from a S14 Nissan 240SX.

The recent failure of my right rear wheel bearing has gotten me thinking about the possibility of converting my current rear suspension to use Infiniti J30 or Nisssan Z rear suspension uprights and OEM Nissan axles. This conversion would also change my bolt pattern to 5x114 and allow me to use whatever wheel offset I want up through the insane lip ranges without having to worry about wheel bearing failure.

I will also most likely convert my front suspension to Mk III Toyota Supra double-wishbone, which is a less major task. The advantages of double wishbone are improved handling, independent camber adjustment and variable kingpin angle (hugely important for establishing scrub radius and wheel offsets). Downsides are the increased number of moving parts and complexity of engineering. Strut suspension is good because it's simple and works with a lot of what I've already got, but the handling and adjustability aren't as good.

The aspect in which I'm looking for input is whether to retain the Subaru lateral link/trailing arm/strut setup, to convert to double wishbone, or to design a combination of suspension systems.

DOUBLE WISHBONE:
Would incorporate 3 main arms; a lower A-arm, an upper A-arm and a TC/Trailing arm. The lower A-arm and TC rod would anchor to the stock lateral link and trailing arm pickups respectively, while the upper A-arm would anchor to new hardpoints along the inside edge of the wheel wells (forward of the fuel filler neck on the right side). This setup would resemble Honda CRX rear suspension, but it would utilize a real lower A-arm and real TC rod rather than a spindle-type arm. Toe control would have to be managed by an additional link on the aft side of the subframe. Lower shock mount would be composed of a pillow ball joint at the end of a bracket that mates to the OEM Subaru strut mount on the top end and to the lower A-arm on the bottom.

LATERAL LINK:
OEM Subaru suspension geometry would be retained, but the donor hubs would be extensively modified to receive 2 lateral links and a trailing arm on each side. My major concern with this setup is that a double wishbone front suspension and strut-style rear will make for poor handling properties.

HYBRID SETUP:
Lateral Links and Trailing arms would both be retained with the addition of an upper A-arm. This would allow for toe control with the accuracy of double-wishbone setup. Clearance may become an issue in this setup, but this is my leading option so far.

Let me know what you guys think. Thanks for any input!

[sheepdog]

of the options you have listed I would go for the double wishbone. It will def be harder to do, but I think youll run into lots of problems with a hybrid setup trying to get it just right. I dunno, I probably wouldnt mess with it at all haha, but if I were going to I would go all out.

[AussieDan]

In all honesty, the amount of work required to do this kind of conversion right would be way beyond what I would consider worthwhile.

If you are serious about the front suspension IMHO the simplest would be to cut in front of the firewall and start again with a tubular frame.

This is kind of what I'm talking about:

http://www.bulletsupercars.com.au/galle ... photoid=48 (http://www.bulletsupercars.com.au/gallery/index.php?p=19&photoid=48)

At that point you can integrate it into your cage and subframe bracing, take the same approach to the rear suspension and you've created a tube-frame race chassis inside your existing wagon body.

Of course, once you've come that far there is little reason to keep what's left of the stock subaru drivetrain, you can stick with the subaru motor if you like but you'd probably get the best results by dumping everything from the flywheel back in favor of a dedicated RWD drivetrain.

[mranlet]

That's a cool link.

I am pretty confident that I'd be able to convert the front to double wishbone since the frame rail travels right below where I would need to mount the upper arm. If I can use what's there that would be better, but if I need to I will tube the front half.

I have been considering a dedicated RWD transmission since the AWD trans' stepper gear is under a lot more stress than it was engineered for and causes a lot of slop between accel and decel. My trans will probably be an American Nissan 240SX transmission due to the good gearing and compatability with Subaru driveshaft splines (Nissan S-chassis driveshaft splines mate to Subaru driveshaft splines).

As for the rear suspension, I think I am going to try to TIG anchoring points for the Subaru lateral links, trailing arm, and strut on to a J30 upright.

My worry is that a conversion to 5x114 in the front (even if it's strut) may cause more problems than it will solve.

Thanks for the input!

[scottzg]

wow, you're amazing.

I would consider swapping in an entire 240sx rear subframe. Sure, it's not as good as a well designed custom suspension, but its a lot better than a marginally designed custom job. You don't have to worry about your home fabricated stuff busting or funky toe control. pillowball is the same as a heim joint, right?

I was under the impression that the j30 had a torsion beam in the rear... i know the maxima does.

For a hybrid set up, how would you mount the upper links to the chassis? Where would you mount your strut (or whatever) so that it doesnt interfere with suspension travel?

As for the front, it seems like it may not be necessary. With the rwd car you dont place as many demands on the front end as an awd one. Heck, losing negative camber at the top of travel can be beneficial under heavy braking.

[mranlet]

I've thought about doing the 240 subframe a long time ago, but the geometry is really pretty retarted, beyond what I could even describe over the interenet without diagrams and such stuffs.

The J30 rear suspension design is similar to 240sx with no torsion bar to be seen. The uprights are designed for ABS and 5-lug brakes as well.

For the additional control arms, I'd weld reenforcement plates to the chassis much like rollcage hardpoints are created. Upper control arms don't have to withstand as much force as lower control arms, so as long as they were solidly anchored to a spar in the frame I think they'd do alright.

Suspension mounts at the uprights would be something that I'd have to determine based on what sort of kingpin angle, efficiency rate, and clearance I'm after. If I have big kingpin angle, I can have big offset wheels with proper scrub radii and more clearance on the inside. The trickiest part would be integrating both an upper control arm and shock mount in the rear.

Oh, and pillow ball = rose joint = heim joint = rod end ;)

[BAC5.2]

I'm sorry I'm not up to date on your current setup, so forgive me. I was RWD for a while, and holy cow is RWD Subaru drifting WILD.

As for the suspension ideas....

The 350Z is setup very awkwardly.

It uses a spring and shock that are independent of each other. This is great for the Z because it's wide as fuck and has lots of room to do this.

The BG, however, doesn't really have this room.

I wasn't sure which Z you were thinking of using, but if you want a 350Z setup, buy a 350Z.

I also don't really understand your motives.

Double wishbones have incredibly interesting setups. You have static camber reguardless of wheel position in it's travel. A Macpherson strut gains negative, then goes positive.

That's really neat, because double wishbone lets you keep a single camber setting, and you can modify the castor to allow more camber gain on wheel turn. Double wishbone is extremely helpful for rear suspension, because you want predictability out of it. If it keeps a single camber setting through it's movement, you can design the damper around that idea, and you can essentially design the system to run without a sway bar.

Personally, I'd optimize the Macpherson Strut setup on a Subaru. If you don't want to worry about wheel bearings, convert to the 05+ STi hubs. Use an 05+ front crossmember, control arms, rear lateral links and hubs, and run some really high quality coilovers.

They are 5x114 and have some crazy wheel bearings.

What are you trying to get out of the car? Are you just trying to drift it? Drift suspension is pretty easy in concept but tough in implimentation.

I think a well designed McPherson strut system can perform equally to double wishbone setups. We work with a professional time-attack race team who runs a stock Subaru system (control arm and lateral links).