Torsion Bar and Shock compromise

[3rdcurve]

Hello fellas,

I finally got to out a few miles on the Dart this year as well as hit the track. While I was happy with the performance at the strip, the road manners are a bit sketchier that I prefer. Here is my current setup.

72 Swinger:
440 with Aluminum heads and accessories
Battery relocated
727 with 3.73 rear
Flaming River quick ratio manual steering box
4 wheel manual disc brakes

Suspension:
Slant 6 Torsion bars
QA1 upper and lower control arms
340 rear springs with offset shackles
Competition Engineering adjustable shocks all around

Wheels and tires:
205/60r15 on 15x7
255/60r15 MT ET streets

How much perforce do I have to give up at the track to get a decent ride and handling? What components will give the best all around performance?

My dad is switching to a rack/pinion coilover setup on his Drag Week Demon, so I will be snagging his adjustable strut rods. Will a front sway bar make a difference, or front/rear combo for that matter? What Torsion bar size will help ride/handling, but not totally ruin the performance at the strip? Are my drag shocks a big reason why the car feels so sketchy going into corners? Realistically, my car will only hit the track a few times a year for fun.... so I want it to feel fun and safe on the road. From all the suspension threads I have read, my handling/grip will be limited by the tread width of my front tires. I know you can fit some meat up there if you go up to an 18" wheel, but that is not the look I prefer on this build. 17" would be max diameter, but if memory serves correctly... I won't gain any extra width with a 17" wheel over a 15". So the next question would be what is the meatiest 15" tire I can fit up front on a 15x7 to make the car a bit more surefooted?
Thanks in advance for the help!

 

[Jim Lusk]

At a minimum you should be running factory 383 bars and sway bar on the street. How much you give up at the strip? I have no idea. Most people buying new bars are going with the PST 1" as they are the best price out there. Your front end is the reason the car won't go around a corner well.

My son's Barracuda had .990" torsion bars, 1.25" front sway bar, .75" rear with KYB shocks. With all sway bars intact and a mildish 383 backed by a four speed and 3.55SG he ran a 14.08 (at 99.8 as I recall) at Fomoso. That was also running stiff sidewall Nascar slicks for drag slicks...Oh, and the rear springs were just a home cobbled up set. He later went to 1.14" torsion bars, but never went to the strip with them.

 

[3rdcurve]

At a minimum you should be running factory 383 bars and sway bar on the street. How much you give up at the strip? I have no idea. Most people buying new bars are going with the PST 1" as they are the best price out there. Your front end is the reason the car won't go around a corner well.

My son's Barracuda had .990" torsion bars, 1.25" front sway bar, .75" rear with KYB shocks. With all sway bars intact and a mildish 383 backed by a four speed and 3.55SG he ran a 14.08 (at 99.8 as I recall) at Fomoso. That was also running stiff sidewall Nascar slicks for drag slicks...Oh, and the rear springs were just a home cobbled up set. He later went to 1.14" torsion bars, but never went to the strip with them.

Thanks for the reply! I ran an 11.99 @112.51 with more traction and tuning I think an 11.7 would be doable. That said, I don't plan on bracket racing, so just a few trips a year for fun.

 

[Oldmanmopar]

340 bars and a stabilizer bar. Take one end link off at the track. These bars will stop the bottoming but still give lift. The stabilizer will get rid of the sketchy lean. I would put 1 inch spaces on the upper control arm bumpers at the track to keep the wheels down. I also moved the rear back 1/2 inch with spacers before I moved the springs in so I left it at that position when I moved them in. This put the original shackles at the correct position to work.
I eventually added Cal tracks but I didn't gain anything noticable. The car weighed 3650 with driver went low to mid 10's with no problem.

 

[72bluNblu]

Hello fellas,

I finally got to out a few miles on the Dart this year as well as hit the track. While I was happy with the performance at the strip, the road manners are a bit sketchier that I prefer. Here is my current setup.

72 Swinger:
440 with Aluminum heads and accessories
Battery relocated
727 with 3.73 rear
Flaming River quick ratio manual steering box
4 wheel manual disc brakes

Suspension:
Slant 6 Torsion bars
QA1 upper and lower control arms
340 rear springs with offset shackles
Competition Engineering adjustable shocks all around

Wheels and tires:
205/60r15 on 15x7
255/60r15 MT ET streets

How much perforce do I have to give up at the track to get a decent ride and handling? What components will give the best all around performance?

My dad is switching to a rack/pinion coilover setup on his Drag Week Demon, so I will be snagging his adjustable strut rods. Will a front sway bar make a difference, or front/rear combo for that matter? What Torsion bar size will help ride/handling, but not totally ruin the performance at the strip? Are my drag shocks a big reason why the car feels so sketchy going into corners? Realistically, my car will only hit the track a few times a year for fun.... so I want it to feel fun and safe on the road. From all the suspension threads I have read, my handling/grip will be limited by the tread width of my front tires. I know you can fit some meat up there if you go up to an 18" wheel, but that is not the look I prefer on this build. 17" would be max diameter, but if memory serves correctly... I won't gain any extra width with a 17" wheel over a 15". So the next question would be what is the meatiest 15" tire I can fit up front on a 15x7 to make the car a bit more surefooted?
Thanks in advance for the help!

The real question is how much do you want to suffer driving the car on the street for your 60' time?

At the strip, a better street going set up really only hurts you at launch because of the changes in weight transfer. Once you're off the line it doesn't make much difference. Slant 6 bars are ridiculous on the street even with a slant 6, let alone a big block.

Your car "feels sketchy" going into corners because you're bottoming out the front suspension every time you put any load on the front end. Slant 6 bars have a wheel rate of 92 lbs/in. Even with 225/60/15's, a small block, and 1" torsion bars with a 200 lb/in wheel rate my Duster was still undersprung up front. The shocks certainly don't help your cause but nothing is going to make up for that wheel rate being about half what it needs to be for half decent handling.

For the set up, it really just depends on what you want and how you use the car. You can keep the 15" wheels and still have a decent handling car, although going to 17's does increase the amount of rubber you can run up front pretty substantially. Your 15x7s can probably take a 225/60/15 if the backspace is decent. With PST's 1.03" bars, a set of bilstein shocks, and front and rear sway bars your car will handle pretty darn good for a street going car. You will likely lose time on your 60' at the track, but you may be able to make some adjustments to get some of that back. And you can always unhook the sway bar end links for a trip down the strip. The other thing is your 340 rear springs. They only have a spring rate of about 110 lbs/in. Even good springs for handling are in the 120-130 lb/in rate, which is still pretty light compared to the Super Stock springs meant for drag racing. Those are like 160 lb/in. So, while going to stiffer springs up front might hurt you some, you may be able to get some of that bite back by changing the rear spring set up too.

With 15's up front about the widest most A-body's can pull off is a 225/60/15. I have seen 235's on a couple of cars, but they get difficult because of the height as well and good luck finding a 235/55/15. With a 17x8 up front and 5.25 to 5.6" of backspace you could run a 255/45/17 if you wanted. And width isn't the only story. You can get much better tire compounds with the tire selection you'll have for the 17's. Running 17x8's and 255/45/17's on all 4 corners with 1.03" torsion bars, 120-130 lb/in rear springs and sway bars would make your car a pretty viable corner carver. Even with 225/60/15's it would handle pretty well. Another option would be to keep the 15's and run those when you go to the track and leave the 17's for street duty. The shorter sidewall on the 17's would likely further hurt your initial launch at the track, especially with the larger bars up front reducing some of your initial weight transfer. But like I said, it really comes down to how much you're willing to suffer with a lousy handling car on the street for a couple trips to the strip a year. I'd rather give up a couple tenths at the strip for a car that isn't sketchy as hell on the street, but that's just me.

 

[3rdcurve]

The real question is how much do you want to suffer driving the car on the street for your 60' time?

At the strip, a better street going set up really only hurts you at launch because of the changes in weight transfer. Once you're off the line it doesn't make much difference. Slant 6 bars are ridiculous on the street even with a slant 6, let alone a big block.

Your car "feels sketchy" going into corners because you're bottoming out the front suspension every time you put any load on the front end. Slant 6 bars have a wheel rate of 92 lbs/in. Even with 225/60/15's, a small block, and 1" torsion bars with a 200 lb/in wheel rate my Duster was still undersprung up front. The shocks certainly don't help your cause but nothing is going to make up for that wheel rate being about half what it needs to be for half decent handling.

For the set up, it really just depends on what you want and how you use the car. You can keep the 15" wheels and still have a decent handling car, although going to 17's does increase the amount of rubber you can run up front pretty substantially. Your 15x7s can probably take a 225/60/15 if the backspace is decent. With PST's 1.03" bars, a set of bilstein shocks, and front and rear sway bars your car will handle pretty darn good for a street going car. You will likely lose time on your 60' at the track, but you may be able to make some adjustments to get some of that back. And you can always unhook the sway bar end links for a trip down the strip. The other thing is your 340 rear springs. They only have a spring rate of about 110 lbs/in. Even good springs for handling are in the 120-130 lb/in rate, which is still pretty light compared to the Super Stock springs meant for drag racing. Those are like 160 lb/in. So, while going to stiffer springs up front might hurt you some, you may be able to get some of that bite back by changing the rear spring set up too.

With 15's up front about the widest most A-body's can pull off is a 225/60/15. I have seen 235's on a couple of cars, but they get difficult because of the height as well and good luck finding a 235/55/15. With a 17x8 up front and 5.25 to 5.6" of backspace you could run a 255/45/17 if you wanted. And width isn't the only story. You can get much better tire compounds with the tire selection you'll have for the 17's. Running 17x8's and 255/45/17's on all 4 corners with 1.03" torsion bars, 120-130 lb/in rear springs and sway bars would make your car a pretty viable corner carver. Even with 225/60/15's it would handle pretty well. Another option would be to keep the 15's and run those when you go to the track and leave the 17's for street duty. The shorter sidewall on the 17's would likely further hurt your initial launch at the track, especially with the larger bars up front reducing some of your initial weight transfer. But like I said, it really comes down to how much you're willing to suffer with a lousy handling car on the street for a couple trips to the strip a year. I'd rather give up a couple tenths at the strip for a car that isn't sketchy as hell on the street, but that's just me.

Thanks for the thorough reply! Honestly 17’s are about perfect to my eye, and the Torque Thrust 2s would keep a similar look. I like the thought of keeping my drag radials and 15s for the track. I already cant hook up on the street even with the drag radials, so making the car safer and more fun on the street makes sense. Not to sound like a weakling, but my flaming river quick ratio manual steering box is already a chore. I’m thinking that with the upgraded rubber up front I will likely want to add the electronic power steering kit. Hopefully I can get the torque thrust with the propped BAckspacing. I used the Dr. Diff kit to run the later 11 3/4” discs up front, which apparently pushes the hub face out further.

 

[72bluNblu]

Thanks for the thorough reply! Honestly 17’s are about perfect to my eye, and the Torque Thrust 2s would keep a similar look. I like the thought of keeping my drag radials and 15s for the track. I already cant hook up on the street even with the drag radials, so making the car safer and more fun on the street makes sense. Not to sound like a weakling, but my flaming river quick ratio manual steering box is already a chore. I’m thinking that with the upgraded rubber up front I will likely want to add the electronic power steering kit. Hopefully I can get the torque thrust with the propped BAckspacing. I used the Dr. Diff kit to run the later 11 3/4” discs up front, which apparently pushes the hub face out further.

The 11 3/4” disks widen the track the same as the regular 73+ disk brakes. It’s wider than drums or SBP disks but it’s nothing crazy, I use the 73+ disk width for all my recommendations.

I know what you mean with the fast ratio flaming river box. I run a flaming river fast ratio manual steering box on my daily driver Duster with 275/35/18’s though, and I run +6.5*’s of caster too - so it can be done. I don’t know that I would recommend it for most folks, but a 245/45/17 or even a 255/45/17 would be a big difference compared to 275’s. Less positive caster also makes a big difference, although I would try to stay in the +3 to +5* range with the QA1’s because it’s better for stability and counteracting the tendency of the wider front wheels to search out ruts.

You don’t make any mention of what rear axle you have. With your offset shackles if you have an A body 8 3/4 with BBP axles you could run these TT2’s front and rear with 245/45/17’s or even 255/45/17’s. Tire selection is a little better for the 245’s because it’s a very popular size, but there are good choices in 255 as well.

American Racing VN405 Custom Torq-Thrust II Polished Wheels VN405786555

 

[3rdcurve]

The 11 3/4” disks widen the track the same as the regular 73+ disk brakes. It’s wider than drums or SBP disks but it’s nothing crazy, I use the 73+ disk width for all my recommendations.

I know what you mean with the fast ratio flaming river box. I run a flaming river fast ratio manual steering box on my daily driver Duster with 275/35/18’s though, and I run +6.5*’s of caster too - so it can be done. I don’t know that I would recommend it for most folks, but a 245/45/17 or even a 255/45/17 would be a big difference compared to 275’s. Less positive caster also makes a big difference, although I would try to stay in the +3 to +5* range with the QA1’s because it’s better for stability and counteracting the tendency of the wider front wheels to search out ruts.

You don’t make any mention of what rear axle you have. With your offset shackles if you have an A body 8 3/4 with BBP axles you could run these TT2’s front and rear with 245/45/17’s or even 255/45/17’s. Tire selection is a little better for the 245’s because it’s a very popular size, but there are good choices in 255 as well.

American Racing VN405 Custom Torq-Thrust II Polished Wheels VN405786555

Ah, fantastic....glad the 11.75” discs don’t make me an oddball. You must have some Popeye-like forearms from parking that Duster! Sorry I missed the rear end info. I am running an Explorer 8.8 with 2 short side axles. I reached out to SpringsnTHings were I purchased my leafs from, and Laura said my spring rate should be somewhere around 130 lbs. Would this make a good match with the Hotchkis sway bars, or should I go Hellwig?

 

[GMachineDartGT]

Your biggest issue is no spring rate in the front. If the front end isn’t bottoming, the rear wants to come around. On the other hand, when the front end bottoms, you have massive understeer. Given your specs the car sounds like a very poor driver except at the track. I have a stage one suspension kit and torsion bars to get you started with the essentials. Bergmanautocraft.com