Any guidance on my 1970 Duster plans

[poconos_power]

Hey everyone! I was recently lucky enough to pick up a 340 TA engine that has been off the road for about 40 years (going to need to get sent out, but it's complete). It belonged to my Dad's friend and his wife finally convinced him it would go better in a car than sitting in their garage. So I did what any reasonable person would, I bought a car to put it in. I ended up finding a 1970 Duster that was originally a slant 6 automatic. I got lucky the interior is great and it only needs small rust patches in the rear quarters, then I may send it out for paint.

In figuring out what I want this car to be, I have never done a performance build before, and was thinking autocross seems like something I want to do. Though I also want the car to be able to cruise and do road trips and such. So I'm looking for it to be good at multiple things but not great at one thing I suppose, I'm sure my limitation will be my driving skill instead of the car in the beginning, I'm just something that works and lets me get into it and would be an interesting project to get to my goal. I did some research and there are plenty of great options for full coil over conversions on the front, and I'm sure I could do that eventually, but I find the prospect of trying to tune in a t-bar suspension more interesting. I figure I can always upgrade and change in the future. So after a few weeks of lurking and reading here is what I'm thinking, and please let me know what you think about this.

For the rear, I was able to score a new 8.75 rear at Carlisle this past summer to upgrade the previous rear. I was thinking of putting in the Hotchkis geometry corrected leafs.

For the front, I was going to do the Firm Feel reinforcement kit for the k-member, reinforce the lower control arms, get the Firm Feel tubular uppers with the big ball joint (if I replace the spindles), and adjustable strut rods. Poly bushings for everything. Also the car has a pretty big front sway bar currently, though I haven't measured it, but I don't think it's original.

For torsion bars I was thinking 1.08 or 1.12 based on what I'm reading here. However the question is, how do I address the 1" drop from the Hotchkis leafs? Do I get drop spindles or just drop the front using the torsion bars?

And finally I'll replace the power steering box with a better ratio. Perhaps at some point I'll also add frame rail connectors and torque boxes, but I'd like to get driving down the road first at least.

Any thoughts out there about this? I've read a lot of posts saying if you set up a torsion bar suspension correctly, it can be on par with a coil spring setup, but I haven't found the full breakdown or how that can be achieved. This is what I've pieced together from various posts. Thanks!

 

[413]

Sell that TA engine to a restorer and buy better quality aftermarket parts with the money.

 

[RAT ROD AL]

You'll need either a V8 K frame or some conversion engine mounts. and A small block trans.

Nice Duster , by the way.

 

[harrisonm]

Nice car. Looks like F8 green. Stay with F8 green and add some white stripes.
@413 might have a good idea. If you truly do have a TA engine, it will likely be worth enough to buy a complete, running 340 or 360. If you find the right restorer desperate for a TA motor for their T/A or AAR, you might even have enough to buy a really good, running HP V8 with money left over (depending on what you paid for it, of course). Look into it.

 

[Scody21]

I did the full FF kit with 1.03 T bars and front / rear sway bars in my 72 340 4 speed. Have the 20-1 and 16-1 manual steering boxes. I put the 20-1 in and did not feel the change to 16 was necessary.

I had the same idea of Auto-X when I was fixing my car up. If you really want to do Auto-X and not mess up the car, you have to put in at-least frame connectors. If you are planing on heavy Auto-X I would recommend putting in the torque boxes, the floor board cross support, from frame support, panard bar for the rear end to keep the rear end “centered”. There is some other trick things to do based off the T/A a/e body race cars of the day.

 

[Plymouth 65]

Nice solid 70 Duster for a project! A true TA motor would be a nice addition. 65

 

[junkyardhero]

, and was thinking autocross seems like something I want to do. Though I also want the car to be able to cruise and do road trips and such. So I'm looking for it to be good at multiple things but not great at one thing I suppose, I'm sure my limitation will be my driving skill instead of the car in the beginning, I'm just something that works and lets me get into it and would be an interesting project to get to my goal.

good to start with a goal. you can have a car that has good street manners and is great on long trips as long as you don't over do it in any one aspect. suspension wise, if you shoot for the upper middle you're not really leaving a lot on the table and set up correctly it'll still be decent at autox for what your skill level may be.

For the rear, I was able to score a new 8.75 rear at Carlisle this past summer to upgrade the previous rear. I was thinking of putting in the Hotchkis geometry corrected leafs.

excellent. great start.

For the front, I was going to do the Firm Feel reinforcement kit for the k-member, reinforce the lower control arms, get the Firm Feel tubular uppers with the big ball joint (if I replace the spindles), and adjustable strut rods. Poly bushings for everything. Also the car has a pretty big front sway bar currently, though I haven't measured it, but I don't think it's original.

fully endorse reinforcing the K & lowers. FF uppers are nice, as are the SPC. if you stay with stock uppers (which are fine, upgrade them using the moog offset bushings for more caster), adjustable strut rods are nice, but not strictly necessary. we'll come back to the bit about the spindles and sway bar

For torsion bars I was thinking 1.08 or 1.12 based on what I'm reading here. However the question is, how do I address the 1" drop from the Hotchkis leafs? Do I get drop spindles or just drop the front using the torsion bars?

i would go with 1.03 or 1.08's and pair them up with some bilstein RCD or hotchkis shocks, do not cheap out on the shocks or it's a waste to get the big bars. don't worry about the 1" drop on the rear leafs. do not get drop spindles, there is no need.

And finally I'll replace the power steering box with a better ratio. Perhaps at some point I'll also add frame rail connectors and torque boxes, but I'd like to get driving down the road first at least.

all the factory stock power boxes are the same ratio 16:1 you can upgrade to a borgsen unit that is quicker at 14:1 for a decent chunk of change. i would suggest the addition of subframe connectors and torque boxes at the start rather than down the road. two fold: one, it's easier while the car is all apart to weld them in; two a flexible chassis is not a tuneable chassis.

back up there you mentioned swapping out the spindles. it appears that you've got factory drums (from the photo up there) so i'm guessing that you're going to go with an aftermarket disc brake set up? let me be the first to tell you to upgrade it to the factory 73~76 style. there are several reasons for this, but some of the biggest involve availability and price: wheels, brakes, parts. besides that, the stuff just flat out works.

on the sway bar: let's see what you've got. you may be able to incorporate it to your new build.

finally: i would try to do ALL of these upgrades before sending the car out to paint.

 

[Garrett Ellison]

@72bluNblu

 

[Oldmanmopar]

By chance was the T/A engine sitting in a barn with an AAR Cuda .

 

[CRUZE 418]

Sell the engine to restorer that does TA' and AAR Cudas, in a heart beat. All that you need is a 340 or 360 block to build a nice engine. Are the carburetors still on the engine?

 

[72bluNblu]

Hey everyone! I was recently lucky enough to pick up a 340 TA engine that has been off the road for about 40 years (going to need to get sent out, but it's complete). It belonged to my Dad's friend and his wife finally convinced him it would go better in a car than sitting in their garage. So I did what any reasonable person would, I bought a car to put it in. I ended up finding a 1970 Duster that was originally a slant 6 automatic. I got lucky the interior is great and it only needs small rust patches in the rear quarters, then I may send it out for paint.

In figuring out what I want this car to be, I have never done a performance build before, and was thinking autocross seems like something I want to do. Though I also want the car to be able to cruise and do road trips and such. So I'm looking for it to be good at multiple things but not great at one thing I suppose, I'm sure my limitation will be my driving skill instead of the car in the beginning, I'm just something that works and lets me get into it and would be an interesting project to get to my goal. I did some research and there are plenty of great options for full coil over conversions on the front, and I'm sure I could do that eventually, but I find the prospect of trying to tune in a t-bar suspension more interesting. I figure I can always upgrade and change in the future. So after a few weeks of lurking and reading here is what I'm thinking, and please let me know what you think about this.

For the rear, I was able to score a new 8.75 rear at Carlisle this past summer to upgrade the previous rear. I was thinking of putting in the Hotchkis geometry corrected leafs.

For the front, I was going to do the Firm Feel reinforcement kit for the k-member, reinforce the lower control arms, get the Firm Feel tubular uppers with the big ball joint (if I replace the spindles), and adjustable strut rods. Poly bushings for everything. Also the car has a pretty big front sway bar currently, though I haven't measured it, but I don't think it's original.

For torsion bars I was thinking 1.08 or 1.12 based on what I'm reading here. However the question is, how do I address the 1" drop from the Hotchkis leafs? Do I get drop spindles or just drop the front using the torsion bars?

And finally I'll replace the power steering box with a better ratio. Perhaps at some point I'll also add frame rail connectors and torque boxes, but I'd like to get driving down the road first at least.

Any thoughts out there about this? I've read a lot of posts saying if you set up a torsion bar suspension correctly, it can be on par with a coil spring setup, but I haven't found the full breakdown or how that can be achieved. This is what I've pieced together from various posts. Thanks!

View attachment 1716334719

Welcome!

You are correct, there's no reason you need to go to coil-overs to handle well. The geometry of the torsion bar suspension is actually very good, especially if the car is lowered a bit. In fact, the only coil over geometry I've ever seen published was worse than mildly modified torsion bar suspension geometry out of the box. Obviously if you commit to modifying geometry either system can be made to work well, but other than a rack and pinion and some header clearance there's nothing you can do with a coil over conversion that can't be done with torsion bars, there are plenty of aftermarket components available to put the torsion bar suspension on any handling performance level you'd like.

Before I really get into it, what wheels/tires are you planning on running? Because tire choice will absolutely change how you set up the suspension, so if you plan on keeping 15" rims that will be a different plan than if you use 17" or 18" rims- for example, your torsion bar choice will be different. There is precious little in performance tires that are good for AutoX and street use in a 15" wheel. To the point that I would say if your AutoX aspirations go further than just having a little fun here and there you will want your plans to include 18" wheels, because that's really the size you need to be at to get a large enough wheel in the front with a good performance tire for autoX.

 

[DionR]

I like the idea of using the T/A motor, provided you don't grenade it. Unless you need a cash source to finance the build, then I would sell it. Otherwise, drop it in and have a cool piece of history between the fenders.

I like the idea of a T/A or AAR style Duster, just don't put badges on it that say that. But reinforcing the TB suspension makes complete sense for that style build.

As Blu said (beat me to it), if you plan to autocross it, start planning for 17" or 18" wheels as the available tires for the smaller wheels are not performance oriented. I like big brakes and 18" wheels allow for 14" or maybe 15" rotors and you can fit a 275/35R18 on the front without any real body work or flairs. BTW, the big dogs at the Optima event at SEMA all seemed to be running 315/30R18's.

I would suggest PS for autocross, but it's just my gut feel not based on experience. I would guess a manual box would wear you out before a single lap, and I doubt even the 20:1 manual box would be able to keep up with the corners. I would go right to the Borgeson box myself.

 

[poconos_power]

@junkyardhero So I went out and measured my front sway bar, 1.125in it looks like. Also, thanks for the pointers! I was totally thinking of upgrading the spindles, but thats definitely part of the plan now. I'll get a good set, no drop. I'm going to start all the work after the holidays and begin pulling the front apart, and before it goes for paint.

@72bluNblu and @DionR Thanks! I totally didn't think of wheels. I have no plans along those lines right now. Any particular tires you've found work well?

Also @72bluNblu what sort of torsion bar handling parts are you referring to? I may not be looking in the right place, trying to get a better idea of what is out there and what sort of things there are to modify and tweak.


Finally to everyone saying "sell the TA"... No. The reason why has a few aspects to it. The guy who sold it to me did so because he thinks I may just be able to get it running in a car that he'll be able to drive at some point. I got a sweet deal of $1k for it, but with the understanding that I'm going to keep it and use it. It was rebuilt almost 45 years ago, driven around in a Cuda for a bit (not AAR) and then him and my uncle removed it before a road trip to preserve it and well... time went by. Didn't come with a 6 pack intake, but thats ok. Finally, I think it's cool and it'd be neat in this car. If I ever think I'd run it too hard and destroy it, I'll pull it to use on something else, but till then I like this motor, it's the thing that kicked off this whole project, so I'm putting it in.

Also, heres a photo or two of the interior as I bought it.

 

[NC Engine Builder]

Let's see this "TA" 340 you bought for a grand. I say that's almost certainly not possible

 

[CRUZE 418]

It would be interesting to know if the car that it came out of still exists. If it was mine, which it isn't, I would reach out to the TA/AAR community. I would think that the previous owner would understand. The engines performance is no different than any other 340, certainly no bragging rights here. Sounds like you are set on it, so enjoy it!

 

[poconos_power]

Let's see this "TA" 340 you bought for a grand. I say that's almost certainly not possible

When the idea first came up all I knew is it was a 340 there was an attachment to and he had been storing and wanted to see it in a car. Only after I took possession of it is when I ran the numbers and realized what it was. It was just luck. Though I did think it was stored a bit better than it turned out to be. Pretty clean on the inside if the bore scope is any indication. Really it was an excuse to start a project.

Got the Lakewood Scatter Shield that was originally with it too, so that was nice.

 

[RustyRatRod]

Sell that TA engine to a restorer and buy better quality aftermarket parts with the money.

I agree, because there's nothing different about the T/A engine except the offset pushrod holes and rockers. Chrysler didn't even bother to make the intake ports different and they could have. Mega stupid. They didn't even use a solid lifter camshaft with the adjustable rockers and used the same old 340 hydraulic cam. Mega stupid. The only thing that makes the T/A really "special" is the Six Pack setup......IF you still have it. So I agree 100% with @413. Sell it.

 

[RustyRatRod]

View attachment 1716335317View attachment 1716335318


When the idea first came up all I knew is it was a 340 there was an attachment to and he had been storing and wanted to see it in a car. Only after I took possession of it is when I ran the numbers and realized what it was. It was just luck. Though I did think it was stored a bit better than it turned out to be. Pretty clean on the inside if the bore scope is any indication. Really it was an excuse to start a project.

Got the Lakewood Scatter Shield that was originally with it too, so that was nice.

Well it has the right heads and valve gear. Where's the Six Pack? Is T/A cast into the block?

 

[RustyRatRod]

@junkyardhero So I went out and measured my front sway bar, 1.125in it looks like. Also, thanks for the pointers! I was totally thinking of upgrading the spindles, but thats definitely part of the plan now. I'll get a good set, no drop. I'm going to start all the work after the holidays and begin pulling the front apart, and before it goes for paint.

View attachment 1716335078

@72bluNblu and @DionR Thanks! I totally didn't think of wheels. I have no plans along those lines right now. Any particular tires you've found work well?

Also @72bluNblu what sort of torsion bar handling parts are you referring to? I may not be looking in the right place, trying to get a better idea of what is out there and what sort of things there are to modify and tweak.


Finally to everyone saying "sell the TA"... No. The reason why has a few aspects to it. The guy who sold it to me did so because he thinks I may just be able to get it running in a car that he'll be able to drive at some point. I got a sweet deal of $1k for it, but with the understanding that I'm going to keep it and use it. It was rebuilt almost 45 years ago, driven around in a Cuda for a bit (not AAR) and then him and my uncle removed it before a road trip to preserve it and well... time went by. Didn't come with a 6 pack intake, but thats ok. Finally, I think it's cool and it'd be neat in this car. If I ever think I'd run it too hard and destroy it, I'll pull it to use on something else, but till then I like this motor, it's the thing that kicked off this whole project, so I'm putting it in.

Also, heres a photo or two of the interior as I bought it.

View attachment 1716335101View attachment 1716335100

Go for it. Just enter with the understanding that unless you port the snot out of the heads, it will do absolutely nothing more than any other stock headed 340. Nothing. That was the whole point behind the relocated pushrod tubes. To port the heads. So if you don't, they're basically going to waste. But in the end, it'll still be cool regardless. Keep us posted.

 

[junkyardhero]

@junkyardhero So I went out and measured my front sway bar, 1.125in it looks like. Also, thanks for the pointers! I was totally thinking of upgrading the spindles, but thats definitely part of the plan now. I'll get a good set, no drop. I'm going to start all the work after the holidays and begin pulling the front apart, and before it goes for paint.

View attachment 1716335078

@72bluNblu and @DionR Thanks! I totally didn't think of wheels. I have no plans along those lines right now. Any particular tires you've found work well?

addco bar.

what K member do you have? original or the 73~76? do your lower control arms have sway bar end link tabs or are they bare?

the reason i ask is you want to build a system. everything works together, so all the parts need to be correct so you don't have mismatched parts that cause interference or bind.