12:05 Garage- ’70 Duster build

[DionR]

I believe at some point the retractable mechanism was recessed into the rear panel, not on exposed on the floor. Perhaps this was in 73 when they changed the interior panel design to plastic??

It was '74 when they changed it. Still had a retractor on the floor for the lap belt segment, but also a retractor recessed into the body next to the rear seat bottom for the shoulder belt section. So 2 retractors.

I thought about trying to add the structure for the recessed retractor, but not sure how difficult that might be. Doesn't seem like it would make for a difficult retrofit since there is just a big hole at that location in the '73.

 

[72bluNblu]

I got impatient and went out and took some measurements this morning and used the ride tech calculator.

Note: I estimated corner weight based on a total car weight of 3500lbs with me in it. I haven't weighed it with the HDK setup (scales at Moparty were backed up). It was previously 3535 with me and t-bar suspension. I also lost a couple lbs since last year...lol. I also guess at the unsprung weight.

I used a few different corner weights, based on front/rear balance percentage to see how the results would change.

Motion Ratio = .807
55/45 = 400lb spring rate
56/44 = 425lb spring rate
57/43 = 425lb spring rate
58/42 = 425lb spring rate
59/41 = 450lb spring rate
60/40 = 450lb spring rate

Changing the unsprung weight just bounced these results between 400 and 450.

It looks like I did a good job guessing on the initial spring rate and ordering the next size up, 450lb. (sometimes its better to be lucky than good) QA1 doesn't have a 12" 425lb spring. I'm sure I can find another brand, but I doubt it will make much difference, especially since my weights are guestimates. If it's too much and I get some oversteer, I can always loosed the rear bar up. It's full tight right now.

lol! If I had a dollar for every time I went out to my car in my pajamas to measure something I could probably buy a HellCrate for it!

Ok, so with a motion ratio of .807 and a 450 lb spring you should end up with a wheel rate of ~293 lb/in, which is really close to the 300 lb/in wheel rate I run with my 1.12” torsion bars.

Your previous 400 lb/in bars have a wheel rate of ~260 lb/in

I think the 450 lb springs should be a pretty good improvement for you, certainly should cut a little more body roll and give you a good base rate to tune from. There’s still probably more room to go higher, but it will depend on your tire set up and compounds. With the Azeni 615’s at 200 treadwear on my Duster and 275’s up front I’m back to being able to put a little roll into it with spirited mountain road driving. I have a set of Firm Feel 1.18’s sitting in my shop, that’s a 370 lb/in wheel rate. I talked to Firm feel about it, I’m a little skeptical about that big of a jump in WR but they seemed to think it wouldn’t be as crazy as it sounds. Maybe I’ll have to go with some adjustable shocks at some point.

Do either of you have any pictures of the seatbelts as installed? Then I will stop mucking up your thread, Joe. Thanks!

Here you go! Yeah my factory ‘74 retractors were inside the quarter structure behind the door. But the mechanisms were a PITA so I replaced them with the ones from seat belt planet. I just mounted the retractors to the floor where the lap belt anchor was, I don’t recall exactly why I didn’t try to put them in the quarter but they work fine on the floor

 

[DionR]

View attachment 1716153479

Here you go! Yeah my factory ‘74 retractors were inside the quarter structure behind the door. But the mechanisms were a PITA so I replaced them with the ones from seat belt planet. I just mounted the retractors to the floor where the lap belt anchor was, I don’t recall exactly why I didn’t try to put them in the quarter but they work fine on the floor

Thanks!

Ironically, I picked up a set of '75-'76 seatbelts at some point and have them in a drawer in the shop. I kept thinking I might have grabbed a set when a buddy was parting a car out, so during lunch I went and looked and sure enough there they were. So I can build a lower mount for the shoulder retractor if I wanted to.

 

[racerjoe]

lol! If I had a dollar for every time I went out to my car in my pajamas to measure something I could probably buy a HellCrate for it!

Ok, so with a motion ratio of .807 and a 450 lb spring you should end up with a wheel rate of ~293 lb/in, which is really close to the 300 lb/in wheel rate I run with my 1.12” torsion bars.

Your previous 400 lb/in bars have a wheel rate of ~260 lb/in

I think the 450 lb springs should be a pretty good improvement for you, certainly should cut a little more body roll and give you a good base rate to tune from. There’s still probably more room to go higher, but it will depend on your tire set up and compounds. With the Azeni 615’s at 200 treadwear on my Duster and 275’s up front I’m back to being able to put a little roll into it with spirited mountain road driving. I have a set of Firm Feel 1.18’s sitting in my shop, that’s a 370 lb/in wheel rate. I talked to Firm feel about it, I’m a little skeptical about that big of a jump in WR but they seemed to think it wouldn’t be as crazy as it sounds. Maybe I’ll have to go with some adjustable shocks at some point.


View attachment 1716153479

Here you go! Yeah my factory ‘74 retractors were inside the quarter structure behind the door. But the mechanisms were a PITA so I replaced them with the ones from seat belt planet. I just mounted the retractors to the floor where the lap belt anchor was, I don’t recall exactly why I didn’t try to put them in the quarter but they work fine on the floor

Thanks for the comparison. I had 1.08 sway away bars.

Double adjustable shocks are the $hit! Besides being able to tune it on the track, I love that I can tame it down for normal street driving. I will get some for the back in the future.

 

[72bluNblu]

Thanks for the comparison. I had 1.08 sway away bars.

Double adjustable shocks are the $hit! Besides being able to tune it on the track, I love that I can tame it down for normal street driving. I will get some for the back in the future.

Ok, so the 1.08’s wheel rate is ~267 lb/in based on my old calculations. So your 400 lb/in springs would have basically the same wheel rate as the 1.08” torsion bars did.

I’m pretty happy with the non-adjustable Hotchis Fox shocks I’ve got now for what I’m doing with the car, which is 100% street driving. But yeah, when I start doing competitive stuff with it I’m sure being able to have a “race” and a “street” setting will be pretty handy.

 

[racerjoe]

Got coil springs changed out Friday and took it for a cruise to the store. Not sure if they really made a difference in normal ride quality, but it feels like it did.
I had the normal 50 mile drive to the track to autocross. I used my first 3 runs to mess with shock settings, which proved to be a waste of time. I should have just stuck with the ones I used at cruising the coast. It was also a little cool on the morning runs and I could tell the tires weren't gripping enough to really push. My first run in the afternoon session, I knocked 1.5 seconds off my best morning run. On my final run in the afternoon, I knocked another .5 seconds off my best time. There's a regular at this autocross event in a 98 Mustang cobra. The guy has been autocrossing since I was a child. I've never been able to beat him when he is in that car. I looked at the past results and the closest I've gotten to him was 3.5 seconds! Well, this time, I was only .17 seconds behind him! Next time, I beat him!
I can make the car understeer and there's a delicate balance of speed in which it happens. I'm conflicted on if I'm reaching the limit of the 235 front tire, need more front shock tuning, bigger front sway bar, or need an adjustable rear shock or all of this.
At Moparty, Peter also recommended a taller upper ball joint. (What a great guy helping someone out that isn't even using his setup!) I realize this will change camber gain, but it will also improve roll center. I have some thinking and calculating to do, but for the time being, the car is pretty good. I'm sure most have figured out that I tend to overthink things in an effort to optimize what I have before arbitrarily throwing parts at this thing.

 

[HemiDenny]

Got coil springs changed out Friday and took it for a cruise to the store. Not sure if they really made a difference in normal ride quality, but it feels like it did.
I had the normal 50 mile drive to the track to autocross. I used my first 3 runs to mess with shock settings, which proved to be a waste of time. I should have just stuck with the ones I used at cruising the coast. It was also a little cool on the morning runs and I could tell the tires weren't gripping enough to really push. My first run in the afternoon session, I knocked 1.5 seconds off my best morning run. On my final run in the afternoon, I knocked another .5 seconds off my best time. There's a regular at this autocross event in a 98 Mustang cobra. The guy has been autocrossing since I was a child. I've never been able to beat him when he is in that car. I looked at the past results and the closest I've gotten to him was 3.5 seconds! Well, this time, I was only .17 seconds behind him! Next time, I beat him!
I can make the car understeer and there's a delicate balance of speed in which it happens. I'm conflicted on if I'm reaching the limit of the 235 front tire, need more front shock tuning, bigger front sway bar, or need an adjustable rear shock or all of this.
At Moparty, Peter also recommended a taller upper ball joint. (What a great guy helping someone out that isn't even using his setup!) I realize this will change camber gain, but it will also improve roll center. I have some thinking and calculating to do, but for the time being, the car is pretty good. I'm sure most have figured out that I tend to overthink things in an effort to optimize what I have before arbitrarily throwing parts at this thing.

nice job.

You already have a Qa1 1" taller upper ball joint. Standard item on the HDK.

 

[72bluNblu]

Got coil springs changed out Friday and took it for a cruise to the store. Not sure if they really made a difference in normal ride quality, but it feels like it did.
I had the normal 50 mile drive to the track to autocross. I used my first 3 runs to mess with shock settings, which proved to be a waste of time. I should have just stuck with the ones I used at cruising the coast. It was also a little cool on the morning runs and I could tell the tires weren't gripping enough to really push. My first run in the afternoon session, I knocked 1.5 seconds off my best morning run. On my final run in the afternoon, I knocked another .5 seconds off my best time. There's a regular at this autocross event in a 98 Mustang cobra. The guy has been autocrossing since I was a child. I've never been able to beat him when he is in that car. I looked at the past results and the closest I've gotten to him was 3.5 seconds! Well, this time, I was only .17 seconds behind him! Next time, I beat him!
I can make the car understeer and there's a delicate balance of speed in which it happens. I'm conflicted on if I'm reaching the limit of the 235 front tire, need more front shock tuning, bigger front sway bar, or need an adjustable rear shock or all of this.
At Moparty, Peter also recommended a taller upper ball joint. (What a great guy helping someone out that isn't even using his setup!) I realize this will change camber gain, but it will also improve roll center. I have some thinking and calculating to do, but for the time being, the car is pretty good. I'm sure most have figured out that I tend to overthink things in an effort to optimize what I have before arbitrarily throwing parts at this thing.

I think the 235 is probably the biggest factor in your understeer. Being tire limited would also help explain why the shock settings up front aren't making a significant difference for you anymore. You've got them in the ballpark and there's only so much grip so small tuning changes aren't coming through.

But the fact that you've gotten that close to a more modern car with an experienced driver should tell you you're on the right track for your upgrades. You can make the car understeer by going too stiff in the front, so, unless you're still noticing a body roll issue in the front I think my next upgrade would be more tire, not a larger sway bar.

 

[DionR]

I think the 235 is probably the biggest factor in your understeer. Being tire limited would also help explain why the shock settings up front aren't making a significant difference for you anymore. You've got them in the ballpark and there's only so much grip so small tuning changes aren't coming through.

But the fact that you've gotten that close to a more modern car with an experienced driver should tell you you're on the right track for your upgrades. You can make the car understeer by going too stiff in the front, so, unless you're still noticing a body roll issue in the front I think my next upgrade would be more tire, not a larger sway bar.

I vote bigger tire too, but only because a 275+ would look killer on the front of that car.

Joe, you mentioned upgrading the seats elsewhere. Any idea what you plan to do there?

 

[racerjoe]

I vote bigger tire too, but only because a 275+ would look killer on the front of that car.

Joe, you mentioned upgrading the seats elsewhere. Any idea what you plan to do there?

100% it would look badass with a 275 on it! I’ll likely get these wheels widened. I’ll just have to deal with the car being down for however long that takes.

I casually looked at seats and also looked on marketplAce for something used. Ultimately, if I decide to do it, it would be a race day only seat and not a permanent fixture.

 

[DionR]

100% it would look badass with a 275 on it! I’ll likely get these wheels widened. I’ll just have to deal with the car being down for however long that takes.

I casually looked at seats and also looked on marketplAce for something used. Ultimately, if I decide to do it, it would be a race day only seat and not a permanent fixture.

I love spending other people's money.

I've got a set of E30 sport seats I snagged for like $30 years ago. Back was broken on the DS seat, got that fixed and put it back together just a couple of weeks ago. Planning to set them in the '73 at some point and if I like them I will get some new skins and reupholster them myself. Time will tell.

 

[72bluNblu]

I run the ProCar rally series seats in my Duster. You can see them in the picture I posted above for the seat belt. They have nice bolsters to keep you from sliding around in the corners but don't appear out of place even with the rest of the stock interior. The regular size is a bit on the small side, they're fine for me but at 5'8" and 160 lbs I'm not exactly big. They make a XL version that's a bit wider.

Procar 80-1000-51L Procar Rally Series 1000 Seats | Summit Racing

Procar 80-1000-51L-XL Procar Rally XL Recliner Seats | Summit Racing

I ran stock bucket seats in my Challenger for the whole 70k+ miles I drove it before I tore it down for repair, and I have to say I don't think I'd run factory buckets even on the street in anything I was going to be driving a lot. They're just not all that comfortable, especially for a car that take corners with some speed. You're always sliding around on them, even with 3 point belts.

 

[racerjoe]

I run the ProCar rally series seats in my Duster. You can see them in the picture I posted above for the seat belt. They have nice bolsters to keep you from sliding around in the corners but don't appear out of place even with the rest of the stock interior. The regular size is a bit on the small side, they're fine for me but at 5'8" and 160 lbs I'm not exactly big. They make a XL version that's a bit wider.

Procar 80-1000-51L Procar Rally Series 1000 Seats | Summit Racing

Procar 80-1000-51L-XL Procar Rally XL Recliner Seats | Summit Racing

I ran stock bucket seats in my Challenger for the whole 70k+ miles I drove it before I tore it down for repair, and I have to say I don't think I'd run factory buckets even on the street in anything I was going to be driving a lot. They're just not all that comfortable, especially for a car that take corners with some speed. You're always sliding around on them, even with 3 point belts.

I have decent seats and they are very comfortable. They are the TMI low backs and they have some bolstering. I think I need something that is more “racecar” since it would just be a race day deal, I would want it comfortable enough for the hour drive to the track.

 

[racerjoe]

This G3 has been staring at me for months and I've just neglected it. I guess its time to give it some love. My 5.7 came with the engine harness when I bought it and a while back I separated the harness to get rid of the wires I wouldn't be using on a stand alone controller. The harness was long enough to get to my main bulkhead, so why not just use the wires that are already terminated at the various connectors. This saves me time and money. I never looked at the actual wiring in any depth until this week. After digging in, I quickly realized the factory uses a common ground for all the injectors and coils. This means the factory ECM switches the power side. My MS3X requires constant power to the injectors and coils and it switches the ground. Not a big deal, I simply cut the common connections out of the harness so I can make my own. So now I essentially have 2 wires coming from each injector and coil with no factory splices. Those paying attention may ask why didn't I just use the common connection for power to those items. The simple answer is, I currently have the power broken up into right bank/left bank, coil/injector power. After I wired the car this way I thought it was silly to separate each bank of injectors/coils. Until one day a fuse for the left bank injectors somehow wiggled loose while I was driving. The engine still ran on 4 cylinders and got me home. So instead of rewiring everything to reduce the power circuits going out to the engine, I'll keep my unplanned failsafe in tact.
Another fun thing I found, 2 injector wires on the left bank are the same color, which is also the same color as the common (previously ground) wire. The ground is a larger wire gauge, but this is still dumb. This also proves that even though wires are the same color, it would be in your best interest to ring them out with a meter.

Factory common splice that was hidden in the harness. There were 3 of these.

 

[ohmie77]

I would like the pictures of the seat belts installed also, I want to use the factory mount for my retractor but seat belt planet tech says I have to mount a angle bracket to the floor in the back seat area. I have an early 71 Duster that has the removeable shoulder belt. For the 3 point conversion

 

[racerjoe]

Here are some pictures photographer Greg Croft captured at Moparty 2023.

Check out the facial expression of my "crew chief" in the 4th picture. If that doesn't show you how much fun this is, I don't know what will!

 

[racerjoe]

Running in the rain seems like it would be fun, but it gets old after a few runs. Just getting the car moving requires a feather touch to the throttle. It sure does make cool photos though.

Before anyone asks, that is header wrap hanging that tore when I plowed over a cone.

 

[DionR]

Looks great!!

 

[72Duster440]

Nice pics, Gregs a great dude!

 

[racerjoe]

I took some time to educate myself on camber gain and roll center, then took a whole bunch of measurements and did more research on what it would take to either simulate a taller spindle or make another spindle work. Based on my math, I needed the upper ball joint to be approximately 1" taller than the 1" tall one Denny supplies. My spindles are drop in replacements for a M2, they are short. Wilwood make a M2 that they state is taller, but it's only 1/2 taller than mine. I found some 1.5" taller ball joints, but they ultimately weren't going to get the upper control arm where it needed to be. Of course the Wilwood spindle with the 1.5" ball joint would get me there, but that means buying brake hubs and discs also. I didn't want to go there. I had to dig to the depths of the internet, but I ultimately found a 2" taller upper ball joint with the same 1.5" per foot taper I needed. I quickly got them on order and hoped my math was correct.
In the meantime, we are trying a different lower control arm so I can widen the track width a touch, and also replaced the sway bar for some additional tire clearance. Before I took the original setup completely apart, I measured the camber gain so I have something to compare it to. The results are as follows:

Ride height +3 - 1.6 degrees
Ride height +2 - .7 degrees
Ride height +1 - .1 degrees
Ride height - 0 degrees
Ride height -1 - .3
Ride height -1.5 - .7

So this shows 1.6 degrees of total camber gain at full compression. Since the upper control arms are mounted on an angle and measuring the arms seems confusing, I measured the upper ball joint housing at 6.5 degree angle down toward the tire at ride height. I had assumed the ball joint housing angle was the best place to get the arm angle. I assumed the average angle of the arms would be the angle of the ball joint. Guess what, it was. I measured the front arm at 12.7 degrees and the rear arm at .3 degrees, which has a 6.5 degree average.
The goal was to get the upper ball joint angle higher at the tire (angled down toward the center of the car). Some preliminary measurements with the new 2" long ball joints are promising. I'll share the camber gain difference once I have it back on the ground and get the alignment done. I'll also calculate the roll center to see how high it is. Based on what I have read, since the angles of the arms with the 1" ball joint will never intersect, the roll center was in the ground, which puts lots of leverage to make the car roll. Getting the roll center above ground should make a huge impact on the handling. I'm getting anxious!

 

[mpgmike]

My rudimentary understanding of geometry leaves me scratching my head. I eagerly await further details to fill in some blanks. I gave you a "Like" because I love that you're thinking. Where the heck did I put the popcorn??

 

[racerjoe]

My rudimentary understanding of geometry leaves me scratching my head. I eagerly await further details to fill in some blanks. I gave you a "Like" because I love that you're thinking. Where the heck did I put the popcorn??

I'll work out each of the steps for determining the roll center on paper and share them if anyone has interest. It's a bunch of triangle calculations. Fortunately online calculators make it much quicker than when I was in school, and I don't have to remember the formulas!

 

[DionR]

I'll work out each of the steps for determining the roll center on paper and share them if anyone has interest. It's a bunch of triangle calculations. Fortunately online calculators make it much quicker than when I was in school, and I don't have to remember the formulas!

I plan to cheat and use AutoCAD when I map mine.

But I am going to wait until I get some cribbing built so I can get my Duster up in the air to pull the transmission. Just seems like it will be easier then.

 

[racerjoe]

Got the HDK back together and just need to finalize the toe settings. I measured the camber gain with the now 2" taller than stock upper ball joint. I can't seem to find that article or forum post where someone measured the stock suspension with the FMJ spindle. I'd really like to compare what I have now to that setup.

I'm going to try limiting the suspension travel to 4", 2" up, 2" down. This doesn't take bump stop compression so it may be slightly more. I'm thinking with the roll center in a better place, the car shouldn't have as much body roll on hard cornering, so this won't matter. I took measurements in 1/2" increments to increase the resolution of the results.

Ride height +2 - 1.8 degrees
Ride height +1.5 - 1.4 degrees
Ride height +1 - .8 degrees
Ride height +.5 - .4 degrees
Ride height - 0 degrees
Ride height -.5 - .3 degrees
Ride height -1 - .3 degrees
Ride height -1.5 - .6 degrees
Ride height -2 - .6 degrees

I've read .7 degrees per inch is desirable for camber gain. If there's any validity to that, I'd say I've nailed it!

Roll center calculations coming next...

 

[DionR]

Got the HDK back together and just need to finalize the toe settings. I measured the camber gain with the now 2" taller than stock upper ball joint. I can't seem to find that article or forum post where someone measured the stock suspension with the FMJ spindle. I'd really like to compare what I have now to that setup.

I'm going to try limiting the suspension travel to 4", 2" up, 2" down. This doesn't take bump stop compression so it may be slightly more. I'm thinking with the roll center in a better place, the car shouldn't have as much body roll on hard cornering, so this won't matter. I took measurements in 1/2" increments to increase the resolution of the results.

Ride height +2 - 1.8 degrees
Ride height +1.5 - 1.4 degrees
Ride height +1 - .8 degrees
Ride height +.5 - .4 degrees
Ride height - 0 degrees
Ride height -.5 - .3 degrees
Ride height -1 - .3 degrees
Ride height -1.5 - .6 degrees
Ride height -2 - .6 degrees

I've read .7 degrees per inch is desirable for camber gain. If there's any validity to that, I'd say I've nailed it!

Roll center calculations coming next...

Is this the info you were looking for?

Spindle Comparison

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