Torsion Bars... Best Diameter for a Lowered Street / Autocross car?

Syleng1 said
If you don't agree with what I have to say- that's fine move along. My interpretation of the question and my answer is based on my information from 40 years in this hobby and having been a professional mechanic for 20 years- yes even back when these cars were modern. Torsion bars do need pre-load otherwise they twist backwards and snap. There is a left and right side for a reason. I have seen them break when cranked up too high or driving around lowered. Driving on the bump stops are not what these front ends were designed for.

The unequal a-arms on these cars from the factory were designed to operate within a certain range. End of story. If you operate them off the bump stops and you will damage the parts, the ball joints are also bottoming out...they are designed to operate with the shaft at a fixed center starting point and not at the edge of the seal. They need as much movement left of center as they do right of center. The factory has a ride height measurement for a reason. Modifying a car for a particular form of racing is not factory settings so I understand you may not agree with what I am saying.
If you dont like the information that's okay- we can agree to disagree.

I’ll agree with both of you here.
The suspension is designed to operate in a range. Lowering too much without using shorter bump stops is not good. That said, the bigger issue with lowering too much even with short bump stops is the fact you are inducing body roll by lengthening the moment arm. What this means is while lowering drops the center of gravity (good) you are giving the suspension more leverage. This means more roll as you lower. This is why people compensate with large bars and sway bars. You have to get just the right combo of tire height and body height to find the happy medium. The high roll center of the FMJ spindles can help. While the roll center may be higher, the moment arm is short. This prevents body roll and inspires confident handling when combined with a good alignment and tires.
The mopar performance books eluded to this very fact. They suggested minor lowering and the addition of additional roll couple. Mopar performance had their own line of big t bars for this.
Mike Martin’s book from the 80’s explains this well too.