Which wouldn't be the first time a device has been called a "torque arm" when it really isn't one kinematically. I went through this some years ago with Kirban's copy of Buick's GNX arm that is in fact pinned at the chassis end.. Eventually, Kirban stopped trying to call it a torque arm and I think called it a traction arm (even though it's little more than a single center-mounted ladder bar - but I digress).
My understanding is that the solid axle Trans-Am cars of about 10 years ago were 3-link designs, and I have to think they were onto something.
The general approach appears to have been to obtain minimal axle steer and either not worry about anti-squat or count on stiff rear springs (and a light rear bar). At autocross and particularly Pro-Solo you'd likely be giving away a bit at the start.
The TA typically IS associated with a greater amount of anti-squat than the S197's 3-link, though it can be harder to separate anti-squat from axle steer without significantly affecting rear RCH. A/S with a TA typically drops as the car squats, which is probably good sometimes but not always. If you match the TA's A/S, the SVIC will migrate quite a bit longitudinally where with the TA the SVIC is pretty stable, which may be what people are feeling (have to think on that a bit and re-read the TA impressions again).
There probably isn't sufficient allowance in ST* to put 3-link A/S where it is with a TA with a bolt-on mod. You can relocate the axle side pickup (at least according to the 2012 rules I have a .pdf copy of), but not the chassis side pickup (doesn't say you can, based on a very brief scan of stick axle allowances). So you'd have to go about an inch upward at the diff assuming that there is sufficient room to do so and you have the wherewithal to pull it off safely/securely.
For a 3-link I'd be considering ways to soften the UCA bushings in the roll and axle steer modes while stiffening them in pure tension/compression of the UCA itself. That short of a UCA exaggerates the forces induced by those rotations.
Substituting a TA begs the question of structural adequacy/durability given the SCCA's position on continuous lateral members in the "lower" categories.
Ahh yes... I fubbed that up!
Thanks for clarifying.
Norm, you are right on the rules, no UCA bracket with multiple mounting holes allowed, just one at the axle side. I don't think there is enough room to do that either from the UCA contacting the floor pan near the UCA mount or the floor pan above the axle. I'd have to look again but I think it is safe to assume it wouldn't be advisable either way.
The only way I can think of allowing the axle to articulate while stiffening up the longitudinal direction and not inducing bind/unintended-spring-rate is some form of spherical bearing with the obvious problem of "bushings may be any material, except metal, and may have no more metal content than the bushing it is replacing". The only solution there is some form of Delrin/hard plastic bushing and that sounds like the wrong place to be using anything resembling plastic. I'm not sure how well Delrin would hold up to those forces when used like a spherical bearing not to mention the pure expense of having them made to fit in the stock diff bushing housing! Yuck! The other option is to do it at the other end of the UCA which is going to be transmitting a lot more NVH and it does afford a little more room for the bearing but it still seems like a bad place for that material.
On the mounting of a torque arm... it does not specify any restrictions other than the restriction in 14.2.H.6 (or 15.2.H.6 for SP) which states:
14.H.6: SFCs may not be used to attach other components (including but not limited to torque arm front mounts or driveshaft loops) and may serve no other purpose.
The Solid axle rules in their entirety:
G. Solid axle suspension allowances:
1. Addition or replacement of suspension stabilizers (linkage connecting the axle housing or DeDion to the chassis, which controls lateral suspension location) is permitted.
2. Traction bars or torque arms may be added or replaced.
3. A Panhard rod may be added or replaced.
4. The upper arm(s) may be removed, replaced, or modified and the upper pickup points on the rear axle housing may be relocated.
5. The lower arms may not be altered, except as permitted under Section 14.8.B, or relocated. Methods of attachment and attachment points are unrestricted but may serve no other purpose (e.g., chassis stiffening). This does not authorize removal of a welded on part of a subframe to accommodate the installation.
Interesting that point 5 includes the section on Methods of Attachment clause. That statement was separated from 5 in the 2012 rules and was assumed to apply to ALL solid axle rules and not the section on LCA's.
Point 2 specifies no restrictions from what I can tell and the only other restriction is the SFC one. I would take that to mean that pretty much anything goes. The only point of contention is whether or not point 5's "Methods of Attachment" clause was meant to be detached and applied to the Solid Axle rules as a whole (see 2012 rules). The only point of contention that I can see then is arguing whether or not the cross member for the torque arm serves another purpose (chassis stiffening). I would think that there isn't ANY way to mount a torque arm other than mounting it to pre-existing cross members or the transmission like the F-Bodies do. I doubt it would ever be protested.
Physically mounting the torque arm, especially the Cortex bit, appears to not interfere with any of the rules I can see since it uses pre-existing bolt holes to bolt on the torque arm. No welding, no cutting, etc. The Griggs unit requires welding the mounts in IIRC, but even theirs doesn't technically fall afoul of the rules from what I can tell since the mount is only used to mount the torque arm and doesn't attach to any subframe connectors (it does attach to the frame rails stamped into the floor pan).
Now if we were talking about an SN95 or Fox car, it would be a little more complicated. To over simplify mounting on the S197, it's basically bolting or welding to the floor pan and mounting at places that have pre-existing reinforcement from the factory.
EDIT: Norm, I'm very much like you. I seek the reasoning behind changes long before I will believe a sales pitch. The quickest decision I made in my suspension was 1 month and that was on the Watts link and that was only on going to a Watts link, not WHICH Watts link. It took me close to 3 months to decide that the Fays2 was the one I wanted. It has taken me 2 years to decide what coilovers to buy, and so on. I think part of it is the financial limitations (I can't afford to buy and try and sell what I don't use) and the other is purely from a "squeeze every ounce of performance out" to gain any advantage I can. In STX, that is a guaranteed requirement since the car is perceived (and most likely is) non-competitive.
