Rallycross Sway bars - Paging Evan and Irish

The car in question is a 1983 Mazda RX7. Light-ish with a stick rear axle with an LSD. It's set up as an IT7 car with a fairly substantial front bar and a smaller but adjustable rear bar set on full hard.
After running one event my impression is that the spring rate is OK, not that I won't change it in the future, but it's workable for now. I think it has too much roll stiffness but I'm not really sure. It was very hard to keep the car in it's happy place. If I had grip then the car would hook and pull the steering way off line. If I didn't have grip then of course the rear would step out but there was only a very very small range between not steering and going completely sideways. Additionally, the car was idiotically stable under braking. Frustratingly so. I'm used to being able to initiate a turn under braking with the 2 and it was frustrating to have the car track completely straight no matter what. There is an adjuster for rear brake bias so maybe I need to mess with that too?
Basically I have no idea how to set up a RWD car for rallycross. My inclination is to ditch the rear bar entirely and try and find the smallest front bar they ever made for the car.

I run no sway bars at all. I have liked the results but I haven't experimented much with a small front bar.

Is the rear suspension different than stock? IIRC stock they had a terrible binding problem in the rear causing you to go infinite rear spring rate with very little lean.

The rear is stock with stiffer springs. Four parallel-ish links with a short panhard bar if sticking my head under the car proves correct. I can certainly see why keeping rubber bushings in the rear would be beneficial.

With the stock 4-link you want to stiffen the front a lot, otherwise you get a sickening snap oversteer effect mid-corner. Rates of about 250 front (with no swaybar) and stock springs rear seems to work okay. With the stock swaybar in the front, 175lb springs up front felt pretty good. Coincidentally enough, I believe the Eibach lowering springs are 175lb front/stock rate rear, and they will actually raise the ride height of a 30 year old Mazda.

The first thing I do with an FB is rip the upper links out of the rear suspension and install something Better. I can sit my pumpkin on a jackstand and articulate the suspension through about 10" of travel without any binding. I'm on 175/175 right now with no swaybars and it feels pretty good on course.

Something.......better?
Do tell.

EDIT: Listen to Knurled, as it's clear that FB RX7 reacts very differently than the e30 does, looking at his post. But here's my original post just in case you want to read it. but it applies to a trailing-arm rear setup obviously.

My early 318 didn't come with a rear bar at all. I'm currently running the stock 318i front bar (it's about as stout as a paperclip) and a 325i rear bar (it's more like two paperclips). So they're pretty marginal as swaybars go. The front is about half as thick as the one on my Triumph, lol.

At our first test&tune next year I plan to try different combos of front unhooked, and both unhooked and see how that works. But I have pretty soft springs so I'm inclined to keep sways to make sure I don't lift the inside rear in corners. Our courses are often hardpack and favor some handling setup that isn't too far off tarmac....not too much tight stuff that requires extra turn-in or rotation - as opposed to some courses I've seen elsewhere that you really need a car that rotates well. YMMV, I know sways always seem to be personal preference.

Hopefully NONACK steps in here. He's driven my car (faster than I have, admittedly) and he said it was the best setup on any of the local RWD cars this year (and he drove most of them since his was always broken, haha...) Granted he didn't drive the class-winner's RX7 (which has stock sways + GC coilovers, I think).

I'd consider ditching the front bar before the rear. The rear-end roll stiffness should help with lift-throttle oversteer in concert with less front roll stiffness. At least in theory. RX7s are strange creatures to me in many ways so what works on an e30 may not work on a RX7 - they're solid rear axle, right?

They are a stick axle.
Part of my problem is that I don't have much front end feel at all. I'm not sure if that's just a matter of the front being so calm and collected after driving FWD cars or what. The only way I could tell the front was pushing (by feel instead of the car going off line) was the steering starting to load up and by then I was usually much deeper into trouble than I wanted to be.

What you do is you cut a big hole in the floor, add a mount to the floor just aft of the big lateral box behind the seats, and add a turret to the top of the rearend with the link mounting point about 4.5" off the rearend housing.

Here's some carnage in progress:

And detail on the rearend crud:

(Photo taken in the middle of swapping housings. The one on top split open up the backside like a well-cracked egg, thus the feeble attempt at trussing the new one)

get some poly steering rack bushings?

mazdeuce wrote: They are a stick axle. Part of my problem is that I don't have much front end feel at all. I'm not sure if that's just a matter of the front being so calm and collected after driving FWD cars or what. The only way I could tell the front was pushing (by feel instead of the car going off line) was the steering starting to load up and by then I was usually much deeper into trouble than I wanted to be.

Nah, you get that, especially with the way light and slow manual steering. You develop a feel for pitching the car around like you're driving a Segway that is steered by a tricycle wheel eight feet away. That's why I'm a fan of depowered power steering, on course it is still flip-the-wheel-with-two-fingers light but at least you don't have to spin the tiller around so much.

Don't listen to what he says about rear sways. That might work on an E30, but the thing with the FB rear suspension is the upper links are not parallel and they are rather short, so they turn into their own sway bar once you get past about an inch of articulation. Thus the mid corner snap oversteer. I saw one FB actually lifting its inside rear tire like a VW while the (stock sprung) front was keeled over with grip.

Part of the reason why I 3-link is that this binding is HARD on chassis. It either rips the upper link mounts off of the body (made easy by the infamous "bin rust"), or if you have a solid shell, the act of using the rear axle as a swaybar tends to twist it. I had one stock-linked rearend that was so twisted that the rear U-joint was angled the wrong way...

irish44j wrote: get some poly steering rack bushings?

Stock FBs have recirculating ball steering...

There's pittman arms and E36 M3 hanging out down there. It's a mess.

Knurled wrote:

irish44j wrote: get some poly steering rack bushings?

Stock FBs have recirculating ball steering...

There's a reason why I posted two things above:

1. Listen to Knurled.

2. RX7s are as foreign to me as Hamid Karzai....and just as wierd.

They're not weird, they're just RX-3s without the leaf springs, or angry looking nose

My (non rallycross) answer to the FB rear control arm issue

upper arms are now equal length with lowers (500mm)

Panhard eliminated 5 rubber bushings for 2 spherical bearings

irish44j wrote:

Knurled wrote:

irish44j wrote: get some poly steering rack bushings?

Stock FBs have recirculating ball steering...

There's a reason why I posted two things above: 1. Listen to Knurled. 2. RX7s are as foreign to me as Hamid Karzai....and just as wierd.

Mazda Motorsports does supply a delrin idler arm bushing that is a big improvement

Knurled wrote: They're not weird, they're just RX-3s without the leaf springs, or angry looking nose

I own a Triumph GT6, so when I say a rear suspension is weird, I have a point of reference, lol.

This isn't going to be one of those "change the bars and the car will be awesome" things, is it?

In reply to mazdeuce:

Not with those upper control arms

mazdeuce wrote: This isn't going to be one of those "change the bars and the car will be awesome" things, is it?

not with that wankel

(only saying that because I'm expected to)

No, it's one of those "the rear suspension doesn't like to move much so stiffen the front to compensate" things.

See: Ford Cortina, Ford Escort. (Specifically see how pretty much every single Ford road racing pic from the 60s-early 70s show the inside front dangling in the air and it doesn't look like the front suspension really moves)

Know how they fixed it in the Escort? They... eliminated the leaf springs (or rendered them no longer locating members) and installed an equal length 4-link and Watts or Panhard.

I'm partial to the 3-link because it doesn't eat up as much interior room, is less fabrication, and it's easier to play with anti-squat and anti-axle torqueover. I have about 50% anti-squat, and I don't know how much anti-torqueover I have but it's better than zero. (Link is angled to the right so that wheel torque tends to compensate for driveshaft torque, reducing the tendency to lift the right tire on acceleration)

Bear in mind, the easiest thing to do right now is just drive the damn thing If it still has road racing spec springs on it then it's probably not too far off as it is.

I'd pull the rear bar off for starters, and either leave the front bar on or find a stock one. Changing the front bar is far more difficult than it really needs to be, so leave it on and see how you do. Believe it or not, a little excess front stiffness HELPS turn the car, it drives the outside tire harder into the dirt.

I also wonder what you've got going on for a rear diff. A tight or welded rear diff WILL make the car a pig if you try to "drive" it around the course.

irish44j wrote: Hopefully NONACK steps in here. He's driven my car (faster than I have, admittedly) and he said it was the best setup on any of the local RWD cars this year (and he drove most of them since his was always broken, haha...) Granted he didn't drive the class-winner's RX7 (which has stock sways + GC coilovers, I think).

Ah, but I have driven that RX7 (fall test and tune). It handled well, but is an FC and therefore is not really relevant to this discussion. Your BMW was definitely best setup, although I think I would run less bar all around since I like to pitch the car into corners harder than you. For your smoother, cleaner driving style, I would think you'd want less rear bar so that the car is less likely to do something scary with the back end mid-corner. Actually, I think that car would do well with less roll stiffness back there regardless of driving style- I don't really see a point in constraining the trailing arms together when they've got decent camber curves unless bump steer becomes an issue.

To the OP, everything I know about the FB agrees with what Knurled has to say- the easiest way without changing the lousy rear geometry is to stiffen the front to try to keep everything in line at the back. I'd also agree that more stiffness up front will help with initial turn-in, although mid corner corrections may be harder to make as a result. EDIT: Also in for more information about the diff, you are giving us a textbook description of all of the potential bad characteristics that come with having a spool.

What do you mean? If I try to drive clean? So I should be trying to slide the car constantly? That's going to take some getting used to. Driving the 2 tidy was almost always the fastest way.
For now I'll mostly be just driving because I really do need to learn how to listen to what the car is doing underneath me. It's all pretty foreign right now.