Someone needs to make splined t-bars adapters.

The benifit would be these are gundrilled and can be had in all different sizes but with the same 1.5" 48 spline broach. B and E bodies would benefit the most being able to go past what is possible with stock hexes. These are all over ebay for $150 pair in 37.5" length.

I'd like to see what rate you could get to where you could crack the windshield. We had to stop testing on the shaker rig because we almost did.

If you really want to easily swap between splined torsionbars I think you could fab something like this, to slide into the existing LCA and TBar anchor, and install the torsionbar in between;

(Quick Photoshop-mockup. Dimensions are wrong)

Come to think of it, the above won't work with fixed tbar anchors.
(I was thinking about the removable anchors the pre'65 fullsize Mopars have.)

The rear hexes need to be 86'd for the female sleeve. Like I said earlier, it would have to be a conversion not an adaptation.

Just a brainstorm, carry on.

IMO Mopars are for sure sprung way to lite from the factory but...
( again IMO) there comes a point when too stiff of a torsion bar just masks the real issue of the front end geometry not being optimal. Too stiff and you basically have little or no suspension, so the negative movement's don't happen, it's just a bigger go-cart. With Mopar's and any unibody design the whole car is a big torsion bar. I'f you limit it too much in one area it has to flex at the next weakest spot. Popped spot welds, ripped out mounts, broken windshields etc...
Unless your doing some serious high speed/high banked road course racing I'm guessing Firm Feel has us all covered?
If your building a dedicated race car that's a different story, they are a "consumable" and not intended to last indefinitely. "Lifespan" is below being competitive on a priority list. No one builds race cars to last 40 years. Most everyone on here runs our cars mainly on the street .
Just my

Just did a few calculations:

Hex opening: 1,25" - no larger TB can be fitted through the TB anchor.
1,5" spline bar ends have enough meat to be machined down to a hex of 1,25" (distance between opposite flat sides not corners).

So if you get splined bars with 1,5" ends and a diameter no larger than 1,25" you could turn them into regular hex bars if you have access to the necessary machining equipment.

Unfortunately most bars I keep finding in the right diameter are only 37.5" long...

Cudazappa (Gary) - The 1.24 TBs are rated at 425 lbs/in. As you know, my car was originally setup for national SCCA Solo II competition (first it was F/Stock, later E/Street Prepared.. a great fun class!)... flat smooth courses (airports, huge parking lots, etc). Progressively changing the TBs also went with changing the rear leafs, as well as the shocks... eventually changing the valving on the Konis to better match the TBs and leafs. The sway bars were also progressively changed in their diameters... fine tuning them with the different combos of end-link bushings (rubber/poly), same with the adjustability of the Koni shocks -- all to my personal satisfaction, as well as with input and track-testing (pylon events) by a few highly regarded and pro-racers. Limits were restricted by SCCA class rules.

After campaigning it for well over 20 years, fine-tuning, etc, it handles pretty good and will keep up with anything out there (and I've taken a break/hiatus sionce ~2001 ~2010). Just ask anyone who's driven or raced it. The ultimate matter depends upon having fresh soft tires, and the skill of the driver on that given day. also, pylon courses mandate the driver to memorize the course layout, and positioning of the car, etc -- a huge factor in time for any day's competition autocross results; road courses also mandate familiarization, and lapping experience is a plus!

Hi-speed road course events is what I've been doing for the past 3-4 years as time and $$ allows -- car handles great... pretty much the same setup as I've settled upon many years ago (actually, its a little heavier with minor changes). Again, limiting factors are just the tires.

Street/hwy driving with the car's stiff setup is no big deal... no cracks, broken welds, windshiled, etc... I have different rims/tires pending where/what I'm doing with the car; naturally, driving on the "street" requires avoiding pot-holes, slow-crossing over RR tracks, etc... I've said before... "street" driving doesn't count as you can't truly enjoy the car; highway driving is great and very enjoyable!... typically 1-2-3 hour (sometimes longer, even cross-country!) driving is no problem... comfort is a-ok.

In retrospect, look at the size of the Posey TA/Gurney AAR cars' TBs (and leaf springs)... I beleieve the TBs are ~1.4+" diameter... of course full roll-cages, re-welding, etc.... and where they are intended to be driven... smooth road courses.... So, the 1.24 are pretty small, on that note.

FF will make the 1.24 TBs for anyone interested, or 1.22, or 1.20 (they already offer 1.18)... and for most Mopar ppl, if they eventually choose increasing the TB size and rate, they will find them to be one of the best overall improvements... BUT, its a "package" of other mods that have to follow... leafs, shocks, sway bars... bushings, steering box/wheel, driver's seat, vehicle weight reduction, weight balancing (side-to-side). Also, I'm certain that adding SFC, and re-welding the k-frame, adding a roll-bar/cage, etc., will help for the unibody's torsional rigidity... honestly, that's one thing I've never done (again, SCCA rules restrictions/limitations in the past classes that I've run)... Some of those rules have since changed, so, I'll probably eventually add welded-in SFC), also, I may even change the setup towards other club's class rules, etc -- but always following a "rule book" so that the mods are not done foolishly with wasted $$$ (so many items items out there offered by different companies, don't fit within certain club's allowable "rules", so, be careful!). The car is rust free and has survived extremely well throughout all of its competative years... and street/hwy driving, too! Its very enjoyable to drive anywhere, anytime.

Not sure if it would work or be practical..... But could you run t-bars and coil-overs to get the desired spring rate?

340duster -- good idea! I've never even thought of that, but not sure if any such options existed back then or even now. The current setup works great for me and has proved itself very well.

Regarding coil-overs, John Sandbergs SCCA C/Prepared AAR eventually ousted the TBs (1.24) and he went to yet stiffer rate coil overs (becuase the 1.24 TBs weren't stiff enough... and had he considered swapping hexes he would have done that but concentrated on the entirely new setup instead).. and the class rules permitted the swap.... he did the same in the rear (ousting the metal xxhd leafs)... he completely re-designed the suspension front and rear (professionally engineered).. result: eventual higher class finishes/more wins and the SCCA national championship C/PL crown. There's a place for coil overs when the TBs aren't stiff enough. Suspension travel remains acceptable for the intended roads/courses driven (always following club rules!, etc). His previous TB/leaf complete overall setup, etc, now resides in his son's 73 440-6 Challenger (also has full fiberglass front end)... street/hwy driven, occasional road course lapping sessions.. an awesome car!

You can read about John's SCCA C/P AAR in Mopar Action issue August 2006 along with my T/A for most of the details. (John's AAR was also featured in Mopar Collector's Guide about 1-1/2 years ago.)

John did install splined sway bars front/rear.... many variable choices in that segment.

With the current shock technology out there and Firm Feel's willingness to make a custom diameter t-bar, I'd say that the rates are pretty well covered for everyone but all out race efforts. By using custom splined s-bars with modular arms, they will yield better on road handling and ride improvements for a street going car than going to wrist sized t-bars.

If you still need something bigger than a 1.24 t-bar for your race car, you can always convert to C body sockets and talk to Firm Feel about custom t-bars they can tool up for you in the 1.40 range, which is upwards of around 750# wheel rate, or roughly twice what the Hotchkis Challenger is using currently.

The only big advantage I could see of using the splined adapter in a stock suspended mopar would be to give you less expensive bar options so you could carry around dozens of sets to change out for track conditions. Even at that, you are only saving 50% per set, but, you also have all the upfront costs for the adapters.

Yes I agree about the not needing bigger bars. I have 1.12's and a full cage on my setup. I didn't really feel or exhibit any excess body roll and my buddy following me at the track up in Thunderhill West said the same thing. Granted I wasn't going that fast as it is a tighter track mostly in 3rd gear, but I never really felt that the front end was out of control or didn't want to go in the direction I chose to point it.

I have taken as much weight off the front end with fiberglass and aluminum engine parts though. It maybe a different story with big block iron engines. I feel that reducing the front end weight would balance the car even further, only then would I even consider 1.24 torsion bars