Torsion Bars... Best Diameter for a Lowered Street / Autocross car?
Looking for feedback / suggestions on what diameter of torsion bar I should plan to purchase for my 71 Demon. The car will be sporting a 408 stroker and A833, and I plan to run either 17" or 18" wheel/tire combo for both street and track. I consider myself to be an "autocross hobbiest" vs an "enthusiast"... so probably 2-3 track events a year. Otherwise, it will be a fun street car that I want to sit low and handle well. I'm running SPC fully adjustable UCAs, QA1 adjustable strut rods, and factory (reinforced) LCAs. For what it's worth, I likely add on the Hotchkis front & rear sway bars also. I haven't decided on shocks yet...but will probably be either Hotchkis or QA1.
I'm looking at the torsion bar options through Firm Feel. Considering the 1.06, 1.12, and 1.18. I'm okay with a somewhat rough ride on the street considering it will be hard to avoid while being lowered... but not sure which of those 3 options to choose from.
So, let me know your recommendations. If you have photos of your ride with a specific setup, that's even better! And of course, if anyone has a used set they'd be interested in selling... let me know!
Thanks
I run 1.12” Firm Feel torsion bars on my Duster with Hellwig front and rear sway bars, 120 lb/in rear springs, Hotchkis Fox shocks and 275/35/18’s in the front and 295/35/18’s our back. I also have SPC UCA’s, QA1 LCA’s, adjustable strut rods and BAC’s delrin bushings.
Based on your description, I think you’d be fine with 1.12” torsion bars. Especially if you’re lowered any significant amount. On my car I would need to use even stiffer torsion bars to lower further without hitting the bump stops all the time, and I already have the short button style bump stops on my car as well as the earlier QA1’s that add some suspension travel back in. And my car isn’t really super low, it’s about 4” from my Doug’s D453’s to the ground.
The ride with that combination of parts isn’t bad at all, it’s pretty close to a modern performance car. I wouldn’t describe it as harsh at all. Good shocks are the key to controlling the larger torsion bars. If I wasn’t also using my car as my daily driver I would probably go up to 1.14” or 1.18” torsion bars and some 200 tread wear tires.
Just ask a lot of questions on Mopar suspension geometry. Just lowering the torsion bars puts all the other parts out of alignment. Factory mounting points were designed for a certain height and operating range. Heavy or lighter torsion bars are great but also designed to work under a certain amount of preload. If you don’t twist them enough or too much they do funky things. I’m no expert but it is why coil over parts are popular with MoPars doing what you seem to be working toward. IMHO.
Sorry, but this is pretty much all inaccurate.
Lowering the suspension does change the geometry, that’s true. But you seem to be forgetting that these cars were not designed for radial tires. Lowering these cars IMPROVES the suspension geometry for radial tire use- you get better camber curves and a much improved roll center, both of which improve handling.
Yes, if you lower the car you need a new alignment done, but again, that doesn’t mean anything by itself. With the OP’s selection of parts, especially the SPC UCA’s, dialing in modern alignment specs is easy. My car is set up with -1.1* of camber, +6.5* of caster and 1/16” toe at its current ride height. None of those specs were hard to get, there’s plenty of adjustment left in either direction.
And, this “preload” nonsense. Sorry, but it’s nonsense. Preload on a Mopar torsion bar suspension is nothing like a preload on a coil spring suspension. The spring rates of the bars are linear. My 1.12” torsion have a spring rate of 300 lb/in, that’s true no matter how much they’re compressed. With the car on it’s wheels and at ride height the bars have a load equivalent to the weight of the car unless it’s sitting on the bump stops.