Critique My Suspension Plan

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JGC403

JGC403

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The car is my 1976 Duster, going to be replacing the tired 360 that is in it with a high revving 318. Car is a 4 speed, pulled the original 833OD and replaced it with a 833 form a 1968 Barracuda. Manual Steering, Manual Brakes. I'll be lowering the front of the car 1" by turning the Torsion bars down. Stock height rear springs, I figure they will probably sag a little over time.

Plan is to use the car for Auto X and use it on the Street. I would like to run circles around my Dad's 2009 Challenger SRT, lol.

Uni-body:
-K-frame sent to FFI
-Frame connectors
-Front and Rear Torque Boxes
-US Car Tool core support stiffeners
-Maybe J-bars in engine compartment

What I would like to do is, as I add the parts that will stiffen up the chassis; twist the body and see how much each thing on my list does, if any. Cause I don't want to add extra weight that isn't going to do anything for handling.


Rear suspension:
-ESPO springs Rear Leaf Springs 6 Leaf Heavy Duty Stock height (with poly or rubber bushings in front spring eye, suggestions?)
-PST Polygraphite bushings for shackles
-Sway bar
-disc brakes
-FFI Bilstein Shocks

Front Suspension:
-FFI 16:1 manual Steering box
-FFI pitman arm bearing support
-FFI needle bearing idler arm
-FFI tubular upper A-arm
-FFI boxed Lower control Arm
-PST Polygraphite bushings all around, except for Lower control arm will be Rubber
-Adjustable Strut rods from FFI or PST, are they worth it? I need new ones anyways one of the stock ones is bent.
-Bigger Torsion Bars, haven't decided yet, Suggestions?
-Front Sway bar
-11.75 Disc brakes
-C-body tie-rod ends
-FFI Bilstein Shocks

Will be going to an 18" wheel probably and modern tires.

I think I got everything, suggestions, comments, I'm open to ideas.
 
If I really wanted to compete in curve carving with late model, coil over strut, tuned suspension, I would invest in a different car. All the aftermarket stuff out there aint gonna work together like end to end engineering does.
 
It all sounds pretty good.

You can go with PST 1.03" or Firm Feel's 1.06" or the next size up. I went with PST's 1.03" due to price mostly. I haven't installed them yet.

As far as the lower bushings, you can go with the rubber like your original plan or you an go with PST's polygraphite bushings (that's what I did - again due to the lower cost compared to delrin) or spend some more a go with delrin bushings from Bergman Autocraft. But that will will also "poly" type pivot shafts. Just wanted to throw out some options for you.

As for core support stiffener, you can also go with XV Motorsports core support as an alternate option. Here's the link for that: LOWER RADIATOR SUPPORT

The one thing I didn't see mentioned, or maybe I just missed it, was the strut rods. I went with PST's Strut Rods. I like the design over Firm Feel's, and I know who makes it for PST and they are a very reputable company.

As for the front sway bar, I recommend Hellwig 1 1/8 in. Tubular Sway Bar. There are other brands of course, but the price for the Hellwig was right and you can order it from Summit and get free shipping. Check out my thread on this. It made a huge difference on stock 40 year old suspension.

All in all, it sounds like you have a good list of parts there. Can't go wrong with Firm Feel from what I've read. I don't know if you will be able to run circles around the SRT, but it will handle quite well.
 
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JGC403 said:
The car is my 1976 Duster, going to be replacing the tired 360 that is in it with a high revving 318. Car is a 4 speed, pulled the original 833OD and replaced it with a 833 form a 1968 Barracuda. Manual Steering, Manual Brakes. I'll be lowering the front of the car 1" by turning the Torsion bars down. Stock height rear springs, I figure they will probably sag a little over time.

Plan is to use the car for Auto X and use it on the Street. I would like to run circles around my Dad's 2009 Challenger SRT, lol.

Uni-body:
-K-frame sent to FFI
-Frame connectors
-Front and Rear Torque Boxes
-US Car Tool core support stiffeners
-Maybe J-bars in engine compartment

What I would like to do is, as I add the parts that will stiffen up the chassis; twist the body and see how much each thing on my list does, if any. Cause I don't want to add extra weight that isn't going to do anything for handling.


Rear suspension:
-ESPO springs Rear Leaf Springs 6 Leaf Heavy Duty Stock height (with poly or rubber bushings in front spring eye, suggestions?)
-PST Polygraphite bushings for shackles
-Sway bar
-disc brakes
-FFI Bilstein Shocks

Front Suspension:
-FFI 16:1 manual Steering box
-FFI pitman arm bearing support
-FFI needle bearing idler arm
-FFI tubular upper A-arm
-FFI boxed Lower control Arm
-PST Polygraphite bushings all around, except for Lower control arm will be Rubber
-Adjustable Strut rods from FFI or PST, are they worth it? I need new ones anyways one of the stock ones is bent.
-Bigger Torsion Bars, haven't decided yet, Suggestions?
-Front Sway bar
-11.75 Disc brakes
-C-body tie-rod ends
-FFI Bilstein Shocks

Will be going to an 18" wheel probably and modern tires.

I think I got everything, suggestions, comments, I'm open to ideas.
Click to expand...


I'd ditch the Bilsteins personally and get you some adjustable shocks. I've been doing autoX since I was 16, if you're trying to measure against modern suspension designed cars, you're gonna need every bit of advantage you can get and an adjustable shock is gonna help you alot in that aspect.

Outside of that, run the most rubber(tire) up front that you can possibly get under the car.
 
I would look at rear springs at least 1" or more below stock height, I would get a local spring shop to build them for you to your own specs.
For the chassis I would weld the k frame and install sub frame connectors, I'm personally not convinced that you need those other stiffing parts, they may just add weight to the car.
I would put a power steering box in the car if you are going to Auto X it, you may not like slow corners and big tires with a 16:1 manual.
You could also try one of the coil front kits that Hemi Denny, Gerst, or RMS sell if you are interest in going in that direction.
Good luck!
 
I think you've got the right idea. Don't listen to the coilover conversion guys. The fastest mopars being autoX'd and used on road tracks have torsion bars. The Hotchkis Taxi, a '70 4 door satellite for crying out loud, is putting down faster times than A-bodies with coilovers. . The coilover front ends are nothing special, they are not magic. Just springs and shocks, just like torsion bars. All suspension systems are a trade off, they have their advantages and disadvantages. The chassis of these cars was never designed to carry suspension loads in the way that the coilovers conversions load the chassis. As far as "end to end engineering", the only end-to-end engineering for these cars was done by the factory, the coilover conversions don't do anything like it.

As far as the rest of it goes-
- 1.06" FFI torsion bars
If your plan is street and AutoX, that's the smallest I'd go. I run 1.12's from Firm Feel, and they're perfectly fine on the street. The ride is definitely firm, but it's not harsh. The right shocks are the key

- Hotchkis Fox shocks
I ran Bilsteins on my Duster and replaced them with the Hotchkis Fox shocks. The difference is small, but it is noticeable. The Hotchkis shocks are better tuned for the larger bars/higher wheel rates. I have Bilsteins on my Challenger which also has 1.12" bars, but they have a 270 lb/in wheel rate compared to the 300 lb/in wheel rate of the A-body 1.12" bars. They're good shocks and better than pretty much everything else out there, but the Hotchkis shocks are better and not insanely more expensive unless you go with the adjustable version. Mine are non-adjustable.

- Adjustable strut rods
You want them. The stock strut rods are a "one size fits most" kind of thing. They were only meant to be close enough to get an alignment. Adjustable strut rods allow you to truly set your LCA's up so they don't have any binding through the useable range of suspension travel, an they do make a difference when it comes to the alignment as well. You shouldn't use the adjustable strut rods to add caster, you should strive to set them up so the LCA's don't bind, but that said they can add some caster when properly adjusted.

-16:1 manual steering
Is great once you're going over 10mph. Below that, it's tough. I run a 16:1 Flaming River box with 275/35/18's up front. For autoX, it may slow down your steering a bit depending on the course and your level of physical fitness. I think it's workable for sure, but it's not a slam dunk guaranteed thing for everyone. I would look at the borgeson power steering conversion if I wanted to go power. 14:1, lighter, etc. You can also run the stock power steering box with a steering quickner (fast ratio steering arms don't clear A-body headers) to get you to 12:1. The Hotchkis challenger runs that set up.

-C-body tie rods
The normal 9/16" tie rod end isn't the weak link, the adjuster tube is. I'd go with a set of solid tie rod sleeves before I went 11/16". PST sells them. I still run the 9/16" ends on my cars, just with solid sleeves. If I went to 11/16" tie rod ends I would definitely use solid adjusters sleeves, it's a waste otherwise.

-Tires
It's all about modern compounds and the widest tires you can jam in there. You'll want to go to 18" rims. Tire selection is better in 18" than it is in 17" now. The other deal is that 17's limit your front tire size. You need to run 9" wide rims to get the widest tires up front, and to do that you need about 6" of backspace for a 9" wide rim. At about ~5.6" of backspace most 17" rims end up with tie rod end clearance issues, 18's clear the tie rod ends because they actually fit inside the rim. You can run 275's up front on an 18x9 with 25-30mm of offset (6" to ~6.2") of backspace. In the back the offset depends on which axle you have, but you can run 275's as well with the stock leaf spring locations and no modifications. I run 295/35/18's on 18x10's, but I have a 1/2" spring offset and cut another 1/2" or so off the quarter lips. It's still pretty tight.

-chassis stiffening
I run subframe connectors, torque boxes, a tubular radiator support brace, J-bars, and have a fully seam welded and gusseted K frame. All of it makes a difference, and none of it adds that much weight. Being a '76, you could shave well over 100 lbs off the car by losing the shock mounted bumpers. You can check my build thread for the rear bumper conversion. In the front you'd have to make your own bumper brackets and lose the impact brace behind the chrome shell. Those bumpers were only rated for 5mph impact protection anyway, above that it doesn't matter.
 
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Listen to 72bluNblu. You don't need coilovers.

My Valiant (originally Tim Werner's), with a good driver (not me), would run circles around a 2009 Challenger in autocross or road racing. Search www.moparts.com for "red brick valiant" or "Tim's Valiant". There is a lot of info on the car on the web. It has torsion bars and leaf springs.
 
Thanks, for the input. You answered a lot of the questions I had. I wanted to keep the torsion bars, I don't see any benefit going to coil overs.

I like the idea of keeping the smaller tie rod ends but with the solid sleeves. It will help keeping the unsprung weight down compared to going to the C-body tie rod ends.

I should be able to run the same size tire in the front if a 1968 Barracuda fastback as the Duster? Should be the same wheel well in the front. The rear of the Barracuda is where it gets smaller, correct?
Reason I ask is i have been looking over the condition of the Dusters body and it isn't that great. I'll start another thread about that. So if I use the Barracuda the plan would be the same except it's an automatic.
 
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The barracuda's are a car I don't have a ton of measurements on. In the front, if anything, there's more room to the fender. The only issue is that the wheel opening is pretty tight, so the barracuda's I've seen with wide tires had to trim back the front corner of the wheel opening. A 275 will fit though, and you'd use the same specs as a Duster or Dart for backspacing/offset since those are basically set off the frame.

In the back I know that autoXcuda was planning on running 275's, but I'm not sure how he was planning on making that work or if it will fit with the springs in the stock location. Barracuda's definitely have more room that Dart's do in the back, but I'm not sure if they have the same amount of room as a Duster.
 
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