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 (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 LCA. 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".

 

[Ozyduster]

And that should be a "Wrap".

Any thoughts on the calvert nine way adjustable for the rear and any ideas what would be a good shock for the front?

 

[lead69]

I really like the viking performance double adjustable shocks.

 

[Ozyduster]

I really like the viking performance double adjustable shocks.

A man of culture is see..... from what i hear bloody good kit. They make some great gear but you pay for it!! I did nearly go the qa1 which 1100 a pair here. In usa dollars thats about 50 cents......... However i do feel i have gone this far and suspension is super important if chasing any kind of time. Two buddies with val chargers both make 550hp one does a 10.2 and the other a low 11. The 10.2 lifts a wheel off the line and just has set up dialed in.

 

[Newbomb Turk]

Any thoughts on the calvert nine way adjustable for the rear and any ideas what would be a good shock for the front?

In my opinion a single adjustable shock is as worthless as a carb that has jets you can’t replace. Or more accurately a carb that you can only use smaller jets.

If you can’t adjust bump and rebound separately the shock is junk.

Yes, lots of guys go fast with them. But not being able to control the shock in both directions separately does not make sense.

 

[HPP]

IMO, for a street car you need a taller front tire. You are going to get a pretty good rake out of the 25/28 difference and trying to adjust the body height to cover the top of both tire is going to make the rake even greater.

I'd also say that if the majority of your time is spent on the street, then build the suspension to live well with good manners there. You won't be giving up much at the drag strip and since you are going to be bracket racing it, ultimate chassis efficiency isn't going to win races over being solidly consistent. Build a nice solid street suspension and live with its times at the strip.

Here is why I say that - I used the same powertrain in two totally different cars. One was a canyon carver built with high rate t-bars and leafs, sway bars on both end, high pressure gas shocks and tires a few sizes below factory Viper sizes. It drove straight as an arrow and cornered like it was on rails. The other car was a dedicated drag racer with a light and loose front end, 90/10 shocks, super stock rear with 50/50 shocks, no sway bars at all and the traditional big and little tire combo, it flew down the strip and cornered like a drunken sailer. I ran the same engine, trans and rear gear combo in each at different times. The handling car would turn 13.2 like it was punching a clock. The drag car would run 12.2 to 12.8 depending on track conditions, weather conditions, and suspension tuning. For as ill mannered as the drag car was doing anything but going straight under full throttle, it wasn't necessarily that much faster overall and it was much harder for me to go rounds in it as I am not a great weather tuner. I went more rounds and went deeper into eliminations with the street oriented car. FYI, but as always, your mileage may vary.

 

[Ozyduster]

IMO, for a street car you need a taller front tire. You are going to get a pretty good rake out of the 25/28 difference and trying to adjust the body height to cover the top of both tire is going to make the rake even greater.

I'd also say that if the majority of your time is spent on the street, then build the suspension to live well with good manners there. You won't be giving up much at the drag strip and since you are going to be bracket racing it, ultimate chassis efficiency isn't going to win races over being solidly consistent. Build a nice solid street suspension and live with its times at the strip.

Here is why I say that - I used the same powertrain in two totally different cars. One was a canyon carver built with high rate t-bars and leafs, sway bars on both end, high pressure gas shocks and tires a few sizes below factory Viper sizes. It drove straight as an arrow and cornered like it was on rails. The other car was a dedicated drag racer with a light and loose front end, 90/10 shocks, super stock rear with 50/50 shocks, no sway bars at all and the traditional big and little tire combo, it flew down the strip and cornered like a drunken sailer. I ran the same engine, trans and rear gear combo in each at different times. The handling car would turn 13.2 like it was punching a clock. The drag car would run 12.2 to 12.8 depending on track conditions, weather conditions, and suspension tuning. For as ill mannered as the drag car was doing anything but going straight under full throttle, it wasn't necessarily that much faster overall and it was much harder for me to go rounds in it as I am not a great weather tuner. I went more rounds and went deeper into eliminations with the street oriented car. FYI, but as always, your mileage may vary.

Noted!!! I purchased the wheels off marketplace with the rubber already on them so can definitely change the front if need be.
Any thoughts on what shocks you would run? For front and rear as have not purchased these items yet.

 

[HPP]

There is a recommendation for Viking in here. They are great shocks. Stocker Star and Varishock are also high quality, aluminum body shocks in single and double adjustable. If you are using Calvert in the rears, they also make units for the front. Of course, Fox and Bilstein are out there on the handling side in fixed rate, steel body. Since you are in Oz, I'd certainly look at what is easily available to you and within your budget range. Not sure what is easily available to you. Shocks are really only limited by your dreams and budget. IMO, they are to the suspension like a camshaft is to the engine. You want the best you can afford that is compatible with the overall package and objectives.

There is a recommendation to avoid anything but double adjustable. I agree in principle because of how well these can be dialed in, BUT would caveat it with your desire to keep very good records of your shock tuning and the results. It's very easy to get off in the wrong direction with double adjustment and if you don't want to keep good records of the changes and want to spend more time just driving, then stay with a fixed rate or single adjustable.

 

[Divenut]

Cool build OP. Welded in Subframe connectors may be a good addition with the kind of power you're making.

Be well

 

[Ozyduster]

Cool build OP. Welded in Subframe connectors may be a good addition with the kind of power you're making.

Be well

Your read my mind, if you look at my build thread i acturally welded in the chassis connectors and front and rear torque boxes last week. About to drop the front end out to seam weld the k frame and gusset around the steering box etc.
Whilst this is happening get the under side of the car painted so i can start bolting it back together. Will be a slow burn tho.

 

[weedburner]

In my opinion a single adjustable shock is as worthless as a carb that has jets you can’t replace. Or more accurately a carb that you can only use smaller jets.

If you can’t adjust bump and rebound separately the shock is junk.

Yes, lots of guys go fast with them. But not being able to control the shock in both directions separately does not make sense.

I run $120 non-adjustables, but not run-of-the-mill 50/50 units. I have a couple sets with different C/R valving as a result of the tuning process, swap them out for changes instead of turning knobs.

Grant