Duster suspension set up questions

[Ozyduster]

So i am in the process of building my 74 duster from ground up, it will run a hemi 6.4, 904 into a 8, 3/4 shortened rear end. I am nearly ready to start putting all the running gear back together.
I want the car to sit low to slightly tuck the rear tyre and similar look up the front. A pr street style look etc, i don't want it scrapping the ground but dont want large gaps from rubber to fender arch
It will be a weekender, probably never even see rain lol and will do the odd pass on the track i am aiming for low tens.
I have a few questions on how to achieve the look and what components etc

Rubber
Rear: 275/60 r15 (28x10.8R15)
Front: 127/80 r17 (25x5 r17)

Currently for the rear suspension i have:
-Calvert split monoleaf with one inch drop with Dr diff offsets
-Caltracks

Will that be low enough or am i way out? What shocks should i run, I am thinking calvert 9 way adjustable would these be ok for racing and street duties?

Currently for the front suspension i have:
-Stock upper arms
-Stock bottom arms with bracing welded in
-Full front end rebuild kit from PST polygraphite kit
-Currently have the torsion bars that wer stock with the 318
-Not sure what shocks to use

What torsion bars should i use to get the height i want and for the hemi weight, i do know guys run the smaller torsion bars to soften the front for racing. But would this work against me for getting it low. Generally how many inches are you trying to knock out to get the guard to the tyre closed up? Would i need to make any other changes?
Also what brand shocks would be goof for racing and street duties

 

[Oldmanmopar]

He should be here any second.

 

[Ozyduster]

He should be here any second.

Hahhaa i think i know who you are talking about........ pretty much in every suspension thread i have dug up. I await on what i should be doing!!

 

[lead69]

Hopefully this helps but here is a pic of my old duster lowered 1" in the back with dr. diff offset hangers and 275/60/15s on 15x8 rims. I had to flatten the bulge in the wheel well above the wheel lip and trim the wheel lip a bit but everything cleared well.

 

[Ozyduster]

Hopefully this helps but here is a pic of my old duster lowered 1" in the back with dr. diff offset hangers and 275/60/15s on 15x8 rims. I had to flatten the bulge in the wheel well above the wheel lip and trim the wheel lip a bit but everything cleared well.

View attachment 1716352153

Mate that looks great!!! I have already cut the outer lips back and re welded them as much as we could, as tubbing doesnt fix that issue. I have my diff guy coming to my factory to measure the diff spot on to try suck the wheels in super close to the springs to try and gain more outer clearance. What did you run in the front?

 

[lead69]

Mate that looks great!!! I have already cut the outer lips back and re welded them as much as we could, as tubbing doesnt fix that issue. I have my diff guy coming to my factory to measure the diff spot on to try suck the wheels in super close to the springs to try and gain more outer clearance. What did you run in the front?

Thanks!, It was kind of an odd size but I found a great deal on a set of 14x6 weld pro stars with 215/70/14 tires which are around 26x8.5.

 

[Ozyduster]

Thanks!, It was kind of an odd size but I found a great deal on a set of 14x6 weld pro stars with 215/70/14 tires which are around 26x8.5.

How do you find it drives with the rear and front that height

 

[72bluNblu]

So i am in the process of building my 74 duster from ground up, it will run a hemi 6.4, 904 into a 8, 3/4 shortened rear end. I am nearly ready to start putting all the running gear back together.
I want the car to sit low to slightly tuck the rear tyre and similar look up the front. A pr street style look etc, i don't want it scrapping the ground but dont want large gaps from rubber to fender arch
It will be a weekender, probably never even see rain lol and will do the odd pass on the track i am aiming for low tens.
I have a few questions on how to achieve the look and what components etc

Rubber
Rear: 275/60 r15 (28x10.8R15)
Front: 127/80 r17 (25x5 r17)

Currently for the rear suspension i have:
-Calvert split monoleaf with one inch drop with Dr diff offsets
-Caltracks

Will that be low enough or am i way out? What shocks should i run, I am thinking calvert 9 way adjustable would these be ok for racing and street duties?

Currently for the front suspension i have:
-Stock upper arms
-Stock bottom arms with bracing welded in
-Full front end rebuild kit from PST polygraphite kit
-Currently have the torsion bars that wer stock with the 318
-Not sure what shocks to use

What torsion bars should i use to get the height i want and for the hemi weight, i do know guys run the smaller torsion bars to soften the front for racing. But would this work against me for getting it low. Generally how many inches are you trying to knock out to get the guard to the tyre closed up? Would i need to make any other changes?
Also what brand shocks would be goof for racing and street duties

In the back you shouldn't have any issues with tucking the tops of the tires into the wheel wells. On my Duster the 295/40/18's I run are 27.3" tall, I run roughly stock height springs and use a spring slider set up that lowered the rear about 3/8". And that set up puts the top of the tire slightly above the quarter lip. It's ~26" to the quarter lip from the ground on my car so even with the weight of the car on the tires they're still tucked in a little. Also, if you're running a 1/2" offset kit and trimmed the quarter lip back you should be able to run 295's if you wanted as long as you get the backspace on the wheels right on.

In the front you're going to have a LOT of work to do, especially if your front tire is only 25" tall. You'd have to lower the front of the car about 2" to get close and honestly even that wouldn't be enough to cover the tops of the tires with only a 25" tall front tire. I run my Duster at just under 25" from the fender opening to the ground, and run 25.6" tall front tires, and they're barely covered because the tires just aren't as tall as the spec when the weight of the car is on them.

If you compare to the factory ride height specs, your A-B has to be 0 where the factory calls for it to be 1 7/8". That's a substantial loss of suspension travel, which isn't good at all for the street. You can get about 1" back by running short lower bump stops, the factory stops are 1 3/8" tall so if you replace those with 3/8" tall bump stops you regain about an 1". On my car, I run QA1 tubular LCA's. The original style that didn't have bump stops had a lower profile than the stock LCA's, resulting in a gain of about 1" of travel. So on my car with 3/8" bump stops and the QA1 LCA's I kept about the same amount of suspension travel as stock.

I run 1.12" torsion bars in the front. Even with a 300 lb/in wheel rate I still occasionally touch the bump stops with street use. It's not enough to be a problem but you couldn't skimp much on the torsion bars without bottoming the suspension quite a bit more in my opinion. Obviously that depends on how you drive the car, I drive in a pretty spirited fashion on some not particularly well maintained mountain roads, so, if you're just cruising around town on the weekends you could get away with smaller bars. Bars that large aren't going to be ideal for drag racing though. You will have an advantage there because your 6.4 Hemi is likely quite a bit lighter than my iron headed 340, so you could probably run something like the 1.08" bars that @BergmanAutoCraft offers between the lighter front end and the difference in driving duties and still be in the ball park for wheel rate. Again, not great for a drag race set up in the front but it will handle and ride better than just lowering it onto the bump stops with the factory bars.

For shocks I've run Hotchkis Fox's and Bilstein RCD's, they work well with the large torsion bars. But they're probably not what you want for the strip.

He should be here any second.

I mean he's asking about a street/strip set up, which is no doubt closer to what you've built than what I have. Why not offer help instead of snide comments?

 

[Ozyduster]

I mean he's asking about a street/strip set up, which is no doubt closer to what you've built than what I have. Why not offer help instead of snide comments?

I think he meant more that you have a lot of knowledge on the suspension of the A body as notice on most suspension comments you have a lot to offer.
My rear wheels are a 8.5inch wide with 3.5inch back space. Took a gamble on them as they were super cheap with bead locks and new rubber
That gives me lot of hope with the rear and guessing the calvert 9 way adjustable will be suffice

 

[72bluNblu]

I think he meant more that you have a lot of knowledge on the suspension of the A body as notice on most suspension comments you have a lot to offer.
My rear wheels are a 8.5inch wide with 3.5inch back space. Took a gamble on them as they were super cheap with bead locks and new rubber
That gives me lot of hope with the rear and guessing the calvert 9 way adjustable will be suffice

I applaud your optimism! But don’t share it, unfortunately.

You’d need more backspace than that with a stock width rear axle, but you’re shortening it right?

Another option in the front is the 2” drop spindles that are available. They add bump steer, but, would allow you to keep your lighter torsion bars which would be better for the strip.

I didn’t want to compromise on the bump steer because I was building a handling ride and needed the larger torsion bars anyway. But if your focus is more strip than street, the 2” drop spindles are probably a better compromise for you. I’ve run them on an E-body, the bump steer is enough to notice when driving it hard on rougher roads. But it’s not enough to be dangerous IMO, and with easier driving it isn’t really noticeable.

 

[Ozyduster]

In the back you shouldn't have any issues with tucking the tops of the tires into the wheel wells. On my Duster the 295/40/18's I run are 27.3" tall, I run roughly stock height springs and use a spring slider set up that lowered the rear about 3/8". And that set up puts the top of the tire slightly above the quarter lip. It's ~26" to the quarter lip from the ground on my car so even with the weight of the car on the tires they're still tucked in a little. Also, if you're running a 1/2" offset kit and trimmed the quarter lip back you should be able to run 295's if you wanted as long as you get the backspace on the wheels right on.

In the front you're going to have a LOT of work to do, especially if your front tire is only 25" tall. You'd have to lower the front of the car about 2" to get close and honestly even that wouldn't be enough to cover the tops of the tires with only a 25" tall front tire. I run my Duster at just under 25" from the fender opening to the ground, and run 25.6" tall front tires, and they're barely covered because the tires just aren't as tall as the spec when the weight of the car is on them.

If you compare to the factory ride height specs, your A-B has to be 0 where the factory calls for it to be 1 7/8". That's a substantial loss of suspension travel, which isn't good at all for the street. You can get about 1" back by running short lower bump stops, the factory stops are 1 3/8" tall so if you replace those with 3/8" tall bump stops you regain about an 1". On my car, I run QA1 tubular LCA's. The original style that didn't have bump stops had a lower profile than the stock LCA's, resulting in a gain of about 1" of travel. So on my car with 3/8" bump stops and the QA1 LCA's I kept about the same amount of suspension travel as stock.

I run 1.12" torsion bars in the front. Even with a 300 lb/in wheel rate I still occasionally touch the bump stops with street use. It's not enough to be a problem but you couldn't skimp much on the torsion bars without bottoming the suspension quite a bit more in my opinion. Obviously that depends on how you drive the car, I drive in a pretty spirited fashion on some not particularly well maintained mountain roads, so, if you're just cruising around town on the weekends you could get away with smaller bars. Bars that large aren't going to be ideal for drag racing though. You will have an advantage there because your 6.4 Hemi is likely quite a bit lighter than my iron headed 340, so you could probably run something like the 1.08" bars that @BergmanAutoCraft offers between the lighter front end and the difference in driving duties and still be in the ball park for wheel rate. Again, not great for a drag race set up in the front but it will handle and ride better than just lowering it onto the bump stops with the factory bars.

For shocks I've run Hotchkis Fox's and Bilstein RCD's, they work well with the large torsion bars. But they're probably not what you want for the strip.

I mean he's asking about a street/strip set up, which is no doubt closer to what you've built than what I have. Why not offer help instead of snide comments?

My front rebuild kit came with mump stops but i think they may be stock height, where did you get your shortened bump stops from?
Also note that using the holley install kit which brings the engine forward an inch. I have also deleted all the reo from behind my bumper bar to try get weight out of the front. No power steering or ac either.

Should note the car will be used to cruise and hopefully go fast in a straight line, not taking it into the hills to fly through twisty roads i have a Lotus 7 for that lol.
My main issue with the tubular front is i most likely cant use them as they dont pass engineering here.

Side note my acquaintance races a valiant sports sedan 358 hemi mid engine trans axel and actually steered me away from the qa1. As believe it or not had had them fold when racing. Same guy is building my 6.4 for me as a bit of a Mopar guru however i don't bust his balls about my car as our whole frienship group always getting help from him

 

[Ozyduster]

I applaud your optimism! But don’t share it, unfortunately.

You’d need more backspace than that with a stock width rear axle, but you’re shortening it right?

Another option in the front is the 2” drop spindles that are available. They add bump steer, but, would allow you to keep your lighter torsion bars which would be better for the strip.

I didn’t want to compromise on the bump steer because I was building a handling ride and needed the larger torsion bars anyway. But if your focus is more strip than street, the 2” drop spindles are probably a better compromise for you. I’ve run them on an E-body, the bump steer is enough to notice when driving it hard on rougher roads. But it’s not enough to be dangerous IMO, and with easier driving it isn’t really noticeable.

Yes its getting shortened as its from a B body so too wide regardless, got it cheap and not a common item in Australia. My diff guy will measure up the car and wheels and hopefully get it bang on haha. But bit of stuffing around as using Ford xr6 turbo 31 spline axles that need to be shortened as well so i can use the modern style brake disks etc.

Ill have a look into the drop spindels i may need to do it after going through the pits as potentially will be an issue ill have to ask the engineer.
Yes as i have seen you built your car to track it? Sorry can you explain bump steer?

 

[lead69]

How do you find it drives with the rear and front that height

I forgot to mention I did have aftermarket upper control arms and a good alignment guy but the rest was stock. It was a 100% streetable car and drove great, I did a lot of long trips to the coast etc. for shows. It definitely was not a lot lower from stock and I only like a little rake so I don't drop the the fronts much but just enough for me, here are a couple more pics to get an idea, hopefully they help.

 

[72bluNblu]

My front rebuild kit came with mump stops but i think they may be stock height, where did you get your shortened bump stops from?

They're from Energy suspension, I run shorter lower bump stops and taller upper bump stops to recenter the suspension travel around the lowered ride height

lowers
Energy Suspension 9.9132G Energy Suspension Bump Stops | Summit Racing

uppers
Energy Suspension 9.9136G Energy Suspension Bump Stops | Summit Racing

Also note that using the holley install kit which brings the engine forward an inch. I have also deleted all the reo from behind my bumper bar to try get weight out of the front. No power steering or ac either.

Should note the car will be used to cruise and hopefully go fast in a straight line, not taking it into the hills to fly through twisty roads i have a Lotus 7 for that lol.
My main issue with the tubular front is i most likely cant use them as they dont pass engineering here.

Side note my acquaintance races a valiant sports sedan 358 hemi mid engine trans axel and actually steered me away from the qa1. As believe it or not had had them fold when racing. Same guy is building my 6.4 for me as a bit of a Mopar guru however i don't bust his balls about my car as our whole frienship group always getting help from him
View attachment 1716352249

Wow! That Valiant is awesome!

I mean, with a set up like that I'm sure he can fold up stock control arms as well with the right conditions. The mopar circuit cars ran suspension stuff that was seriously beefed up over stock. QA1 has added more gusseting to their newer offerings, so I'm not sure how long ago he did that. I had a set of the CAP tubular lowers (before it was bought by QA1) and had a weld fail on those. But CAP went under because of lousy quality control, and QA1 improved both the design and (twice now) and of course the quality improved immediately.

Regardless I know you guys have pretty strict engineering requirements over there so I totally see how that could be an issue for you with those aftermarket LCA's.

Yes its getting shortened as its from a B body so too wide regardless, got it cheap and not a common item in Australia. My diff guy will measure up the car and wheels and hopefully get it bang on haha. But bit of stuffing around as using Ford xr6 turbo 31 spline axles that need to be shortened as well so i can use the modern style brake disks etc.

Ill have a look into the drop spindels i may need to do it after going through the pits as potentially will be an issue ill have to ask the engineer.
Yes as i have seen you built your car to track it? Sorry can you explain bump steer?

Yeah perfect, that makes sense with the B-body rear.

I suppose the drop spindles might be an engineering issue as well. They've been on the market a long time, seems like really splitting hairs but I've heard the engineering criteria for modifications are pretty tough over there. I would think you could get something like that through, but I don't know those requirements or what variances they allow.

Um, another option would be use 73/74 B-body LCA's. They have a completely different profile, but the same length as an A-body spindle. They also have a lower ball joint that's part of the LCA instead of the steering arm, so the steering arm itself is a non-wearing part and the ball joint is a more standard piece. The problem is none of it is reproduced, and I have no idea the availability of 73/74 B-body stuff over there. You basically have to get it all from a donor. The strut rod attachment is also different, so, it would require reworking that which would probably also require engineering on either the LCA or the strut rod, depending on how you did it. Those LCA's have an even lower profile than the QA1 tubular LCA's, they'd add more suspension travel than you could even use without changing the inner fenders (the tires would hit the inner fenders on full compression).

Yeah I built my Duster for autocross, although so far I just street drive it. The nice thing about autocross is that most of what works for autocross also works very well on the street to have a really well handling car.

Bump steer is the toe change through the range of suspension travel. Because of the geometry of the steering arms relative to the control arms and spindles, as everything travels up and down the arcs mean that the wheels will toe in or out because of the relative differences in the diameters of the arcs of each suspension component. This article is on spindle swaps, but it does a really good job of explaining bump steer

https://www.hotrod.com/articles/mopp-0503-swapping-a-and-b-disc-brake-spindles/#google_vignette

 

[Oldmanmopar]

And that should be a "Wrap".