Auto-X / Roadrace rear suspension 1969 Valiant

go-fish said
Not worried about intrusion at all really. I share your concerns with the XV stuff. There are some other things I don't like about it. The lower bars for one would need to be put in the frame rail like the MP inboard relocation. The Reilly Motorsports has an option for OEM mounting location at the front spring hangers or inboard, for which they sell the the frame cut-out. I had seen right off the bat where some changes to the XV kit would be needed. Illiminates a lot of the allure for me.
Not really keen on the triangulated 4-link due to what you stated. Binding, less articulation. It does fine on a street car where an off ramp or clover leaf is as tight as you get but I am after optimum track suspension. I do see than Reilly went to a swivel-link (rebuildable greasable heim joint) that may help a fraction with binding but the articulation is still limited by the uper bars and their angles.
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Great point on using sliders. Some of the reasons I like the composite monoleafs: Cheaper, can buy multiple spring rates. Lighter, can lug multiple sets to the track and swap them out. With a panhard rod you eliminate the side to side movement of the rear axle. I totally forgot about the sliders, thank you.

BTW, I thought the Gurney cars ran composite monoleafs. I was mistaken.

For all these years I was under the assumption that the chassis man was going to do a 3-link. George (my chassis guy) won NMCA-West autocross in 2021 in his torque arm rear / Total Cost Involved front suspension 69 Camaro so he said he wasn't recommending the 3-link anymore. If you pay attention to NMCA West and OUSCI you would see many cars that are way up there in refinement.
Tom Kaman ( Purple Valiant) , who just had his bad *** 70-71 Firebird built by George is running the same TCI/ torque arm suspension and has been winning this year. To my knowledge none of the cars in NMCA Classic American Muscle class are running an independent rear. All solid axle with various rear suspensions. I do believe Mary Pozzi is running an Art Morrison IRS but she is sponsored ($13,000 rear suspension) and runs in SCCA and OUSCI.

If I had F@(% YOU money I would be running the suspension she does, front and rear. IT is way above the capabilities of a torsion bar/ leaf car.

One of the foundational principles of this Valiant build was to continue on with a Valiant that would have been the result of Tom's car if he had continued refining it. I talk to him often about his thoughts on taking it further. We are friends and I see him every once in awhile at the shop. He had an 833 and said he would have gone T56 had he continued so I put that on my shopping list. He would have went with a bigger torsion bar so I went with 1.24" bars. Brakes? He likes my Viper kit. His engine was underpowered so I made sure to have Brian at IMM build an engine specifically to tackle not only autocross but big tracks as well. His car was pretty balanced but he said he would have liked to get a little more weight off the nose so I got a fiberglass hood and may get a fiberglass front bumper.
I have an Alter-k-tion car but I really wanted to stay away from a coilover suspension and build an OEM suspension Green/Red Brick inspired Valiant. Then I met Tom and saw him coming onto the San Diego SCCA scene. By the time I was close to done collecting parts and ready to get chassis work done he had told me that he would have liked to try George's 3-link before selling it. The whole reason he got out of that car was to move onto a different platform that would be more competitive. GM F-bodies. His Valiant was competitive for a moment in time but this sport is ever changing and where we are today, if you want to be at the top of the heap you have to be in a platform that is well supported and be a damn good driver (which Tom is). He could not be competitive in the purple car today. I won't be able to ever be #1 in my Valiant but my particular goal is not to be class winner but to have the fastest Mopar to compete in the class and take out as many brand X cars as possible. I would have to spend $50,000 on suspension and chassis work to be competitive in a Mopar and it would mean not using ANY Mopar parts other than the body and perhaps engine.

Yeah honestly I don't think the "kits" that are out there are designed for what you want to do. I'm not saying that the RMS 4 link kit couldn't be made to work, obviously there are guys out there that have run them in various autoX and track events.

The other thing to consider is the amount of horsepower you're running. 3 links don't usually do great with loads of horsepower, a parallel 4 link might be a better choice. And since you're not worried about cabin intrusion the parallel 4 link wouldn't be an issue for installation (like can be for those that want to retain the rear seat).

The Gurney AAR may have run composite mono leafs at some point, I'm sure it has gone through multiple configurations. That's a good point about being able to have a few different spring rates made and being able to swap them out, getting good quality multileaf springs has definitely been an issue lately and getting more than one spring rate that's in the same ballpark is getting downright difficult. That said, I think setting up a tubular splined sway bar system would probably solve a lot of the spring swapping issues. That's one thing in that XV kit that's a really good idea.

As for not being able to be competitive, I call BS. There's nothing "more competitive" about a GM F-body, other than there being more aftermarket support. The factory motion ratio is abysmal, I mean, running a 900 lb/in spring to get a decent wheel rate? C'mon.

Tom's car beat the stuffing out of modern Mustangs, C6 Corvette's, etc. And to be completely fair, Tom's car was not set up perfectly. He was still undersprung for his tire choices with a 1.06" torsion bar. He was definitely under powered compared to the other competitors at the time, he was running undersized brakes for most of his outings and his transmission/rear end gearing was not ideal. And he still came in second only to Mary Pozzi at an SCCA national event.

I'm not gonna defend the leaf spring rear suspension too hard, a properly set up IRS system is a better deal. But that's not as easy as it sounds, especially given the constraints of putting it into a car designed for something else. All things equal and the IRS wins out, but I do think that A LOT can be accomplished with a leaf spring rear if everything is set up and tuned properly.

The torsion bar suspension is just an unequal length control arm set up, just like EVERYTHING ELSE. Whether or not it works better than some mega bucks aftermarket suspension comes entirely down to tuning. Not all that long ago the tuning advantage other suspension systems had was significant, but that's not the case anymore. With a set of SPC UCA's you can dial in changes in just about every suspension geometry metric there is. Slapping on a set of tubular control arms with a corvette spindle on an F-body does not, in and of itself, make for better suspension. You're still just running parts designed for a different car, and like aftermarket suspension kits designed for the Mopars not all of those kids are really designed for competition, they're designed for rich guys that like shiny things.

There are plenty of cases of torsion bar and even torsion bar/leaf spring Mopars besting cars with much more modern suspension designs. The Hotchkis Challenger pulled a higher skid pad G loading than a modern Challenger SRT. The Hotchkis Taxi lapped faster on TireRack's test track than the 3 series Beemer's they usually use for testing, driven by the TireRack test driver that drives the Beemer's all the time and had never driven a pro-touring Mopar before. And yeah, Tom had a ton of success against modern cars too. Mary Pozzi was fast in the Hotchkis Challenger also, and I think the majority of Mary Pozzi being fast has more to do with her skills as a driver, rather than the megabucks ride she drives.

The biggest advantage to any race suspension is tunability, and you don't need to speed $50k on suspension to get a tunable Mopar suspension.