I'm taking the front suspension apart, noticed my 74 chally with 318 V8 came with the smallest diameter torsion bars mopar offered, 0.862 inch diameter. Did some searches on this forum for Tbar sizing. The T/A and AAR came with 0.92 inch diameter, and 0.88 was a common next size down. Some folks said the 0.92 bars gave a somewhat harsh ride, but handled well in the corners.
Since this car is a true driver, and my wife has neck problems from 2 accidents prior to when we met, I"m leaning away from "lumber wagon" ride quality for the Challenger.
The local parts yard has several cars with the 0.88 Tbars. How will they match up to the 0.92 bars when I include my front end weight savings? Comparing 0.88 to 0.92 gives 0.04 diam difference. 10% of 0.88 is 0.088, so 5% is 0.044. So the TA AAR bars are about 5% larger in diameter than the 0.88 bars.
Now looking at the weight savings on the car: alum cyl heads=50 lb, intake manifold=20 lb, battery in trunk takes 60 lb off the nose. So far have 130 lb., now the battery is behind the rear axle so assume another 10 lb off the front wheels for a total of 140 lb.
Car weighs about 3200 lb. Assume 60% of this weight is over the front wheels = 1920 lb. Reduce that amount by 7.2% = 138 lb. which is real close to my weight removed from the nose. That 7.2% lighter front end is more than the 5% increase in stiffness of the TA AAR Tbars, so I'm going to say the weight savings is about equal to the increase in stiffness of the 0.92 TA AAR torsion bars. This means with my weight savings I can run the 0.88 Tbars and have the handling of the 0.92 bars.
Now looking at the weight on the front and rear wheels. OEM front weight was 1920 lb, so OEM rear wheel weight was 3200-1920= 1280 lb. With 140 lb weight reduction front weight= 1780 lb. Now add the 60 lb. battery weight to rear wheels= 1340 lb. Total car weight is 1780+1340=3120 lb. Amount of weight over front wheels is 3120x.57=1778, so about 57% of weight is over front wheels. Thats better than the 60% I started with.
Now just to experiment, add 80 lb BEHIND the rear axle, so total car weight is back up to 3200 lb we started with. Assume another 10 lb off the front wheels, so front wheel weight is 1780-10=1770 lb, and rear weight is now 1340+80=1420 lb. Percent of weight over front wheels is 3200x.55=1760 lb. So weight over front wheels is just about 55%, and rear wheel weight is then 45%. This 55/45 weight balance is supposed to be a decent balance for front engine/rear wheel drive cars.
So I'm going to do my weight reductions, install 0.88 torsion bars, battery in trunk, set the car ride height level front to rear, align per specs in the suspension section of this forum, then experiment with and without the extra 80lb in the trunk.