Suspension/Chassis Suggestions

Suspension/Chassis Suggestions - 70 Dart Swinger

pyrogen007 said
I have read through quite a few suspension threads and find myself more confused/undecided than when I started. I am looking for suggestions on how to proceed in regard to the suspension and chassis setup, the end goal is to have a sporty daily driver. Initially, just to get it running/driving I am installing an 80s truck 318 but I have a 2/3 complete 451 stroker with aluminum heads I might install later. I have some time to save up as I am still putting it back together but priority is getting this car running and driving and upgrading over time, I just need a solid plan on how to meet my goal, below is what I have:

Car info:
70 Dodge Dart Swinger 2 dr Hardtop
225 CI 6cyl - removed and sold
3 spd auto on column - removed, converting to 4 spd
7 1/4 rear axle
4 wheel drums

Suspension/Chassis Parts I have:
Refurbished factory 73+ UCAs, LCAs, strut rods, V8 K frame and disc brake spindles with Energy suspension's Poly Master kit
Stock replacement ball joints
Wilwood Dynalite Pro front disc brakes, 10.75" diameter vented rotors - 4.5" bolt pattern
6 cyl Torsion bars - still in the car
6 cyl Leaf springs - still in the car
8 3/4 housing w/ 489 sure grip center
axle shafts - 4.5" bolt pattern
10 or 11in drums, I believe I have both
Factory power steering gear box
Stock tie rod ends, adjusters, pitman arm and idler arm
Comp Engineering 3 way adjustable drag shocks - probably won't use these.

These are the parts that I believe that I need to purchase to increase the performance of the suspension to meet my goal, what would the priority be in order of greatest benefit first?

Torsion bars
Rear leaf springs
Shocks
Sway bars(front & rear)
Chassis stiffening
UCA upgrade
LCA upgrade
Ajustable/dynamic Strut rods
Delrin bushings
Wheels
Tires

The 6cyl suspension is still in the car because I have been working on the body and rebuilding the HVAC. The rebuilt stuff is not in the car yet so now is the time to weld in the reinforcements to the LCAs and K Frame I assume. I also assume that torsion bars, leaf springs and shocks should be installed at the same time as the front and rear axle assys, please correct me if I'm wrong.

Thanks for the help!!

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I think @abodyjoe pretty well covered it, the one thing I haven't seen mentioned yet is what wheels/tires you're going to put on the car, which is really the place you need to start.

If you're set on keeping 15" wheels on the car then you don't need to go super crazy with the wheel rates, which plays a big part of what torsion bars you'll run up front. You just can't get really grippy DOT legal tires in the 15" wheel diameter for a street car. If you stay with 15's I'd put the torsion bars in the 1.03" to 1.08" range. More than that will be over sprung for the amount of traction you have.

If you're willing to go to 17's or 18's, well, you can get MUCH better tires and therefore can make use of larger torsion bars. I run 275/35/18's on the front of my Duster with 200 tread wear tires, and even with 1.12" torsion bars and Hellwig sway bars there's room to go to larger bars without being over sprung, and that's with a 340 up from (although with iron heads).

Wheel diameter and tire choice also effects the brakes, with 15's on there the 11.75" 73+ mopar disks work really well, same for the 11x2.5" rear drums. I actually ran that set up on my Challenger with 275/40/17's on all 4 corners and the brakes kept up, although I was running a harder tread compound at the time. If you go to 17" or 18" wheels you can run 13" disks up front, with the 275/35/18's on the front of my Duster I went from 11.75's to a DoctorDiff 13" cobra kit and then more recently to the 13" DoctorDiff Viper kit up front, the change to a much softer tread compound allowed additional braking upgrades.

The shocks thing is also VERY important, cheap shocks do NOT keep up with larger torsion bars. KYB's will absolutely ruin your ride quality with bars over 1" in diameter (they suck all the time, but it becomes even more obvious with larger bars). I know, I've done it. I ran KYB's on my Challenger with 1.12" torsion bars for an embarrassingly long time, changing them out for RCD Bilsteins was a night and day kind of improvement.

In the back the leafs are just fine with a decent sway bar, you want to be in the 120-140 lb/in range depending on how the car is set up. 130 lb/in is pretty much the sweet spot. These cars are nose heavy, and they were not nearly as under sprung from the factory in the back as they were in the front compared to a modern car. With my Duster I run 121 lb/in rear springs with my 1.12" torsion bars up front, which are a 300 lb/in rate. I run a slightly larger 7/8" rear sway bar, and on the road the car is well balanced. Calculators are nice and all but when you throw the car into a corner it gets obvious what it wants. Some of that is driver preference too, I personally believe in not being in oversteer already because on a higher HP RWD car it's easy to add some oversteer with the throttle. If you start off in oversteer mode already it takes your throttle option out of the mix a bit.

pyrogen007 said
I have noticed that no one has mentioned mini-tub/spring relocation for wider tires. I assume moving the leaves inward adversely affects road handling?

So far, I'm getting some pretty good info that isn't contradicting in the same manor as some of the other suspension threads, so thanks everyone for the great replies! I really appreciate it.

A 3" relocation does change how the car handles, but it's easy enough to offset with the rear leaf spring rate. For a 3" relocation if you add 10-15 lb/in you're back in the ballpark, or even just a larger rear sway bar. An E-body rear sway bar actually works well with a 3" relocation and is larger in diameter than what you get for an A-body.

But in order for the 3" relocation to be worth it you MUST do a mini-tub. Without the sheet metal work you only get about an extra 1/2" of clearance moving the springs, because that's all the room there is in the stock tubs.

Which brings up another option, DoctorDiff sells a nice 1/2" spring offset. It's just hangers/shackles, so it bolts into the car and doesn't require any cutting on the body. It does still need the spring perches to be moved, but since you're replacing a 7.25" you may be doing that anyway. And even with an A-body 8 3/4 you've got it out of the car and a perch move isn't all that hard.

Which one you need depends on what you want for tires. 100% stock you've only got room for 255's in the back, maybe even only 245's depending on your car's body tolerances. With a 1/2" offset you can squeeze 275's in there, and if you're going to 18" wheels you can run 275's on all 4 corners without too much trimming/rolling.

On a Dart, if you want to go bigger than 275's you'll need the 3" offset and mini-tub. But that will open you up to run all the way to 335's if you want.