How much chassis stiffening needed?

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rr4406pak

rr4406pak

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Well, finally got the word from the machine shop that my 440 block is good to go!
Dropping a built 440 into my 1969 Slant 6 Dart.

Question: I figure on making around 550HP with this engine (maybe a 150hp shot of nitro down the road). Would just welding in subframe connectors be enough for the chassis to handle the power or would I need more?
*This will be mainly street driven tire burner but I intend to participate in events like Drag Week as well.
Thanks.
 
I think the factory cars only had torque boxes so I would think that subframe connectors would be stiffer than at least that. But I agree with @toolmanmike with just springing for both subframe connectors and torque boxes, stiffer is better imo
 
Projectile Dart said:
I think the factory cars only had torque boxes so I would think that subframe connectors would be stiffer than at least that. But I agree with @toolmanmike with just springing for both subframe connectors and torque boxes, stiffer is better imo
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Not quite sure what you mean by factory cars, but my 340 cuda has all four of them (torque boxes). Agree that torque boxes and "heavy" torsion bars (1.03 or bigger) as well.
 
A56 said:
Not quite sure what you mean by factory cars, but my 340 cuda has all four of them (torque boxes). Agree that torque boxes and "heavy" torsion bars (1.03 or bigger) as well.
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Some cars had all 4, some had rears only. I have yet to see factory information which cars had what combination other than convertibles were supposed to have them on all 4 corners. You want a solid car? Add all 4 and subframe connectors. Torsion bars and suspension mods go from there depending on how you are going to use the car.
 
When you stop twisting and breaking stuff, that’s when your done. 550-700 is a lot of juice. I would throw everything us cartool has at it and a roll cage as well.
 
toolmanmike said:
Some cars had all 4, some had rears only. I have yet to see factory information which cars had what combination other than convertibles were supposed to have them on all 4 corners. You want a solid car? Add all 4 and subframe connectors. Torsion bars and suspension mods go from there depending on how you are going to use the car.
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Yep, appears this car is more street driven and that heavy front end on /6 torsion bars is a potential corner washout. Still "factory cars" definition?
 
Frame connectors and a 10 point cage. The 111 inch longer dart flex quite a bit more then the 108 cars and that square roof doesn't prevent much flex. One other thing to consider is will a family member ever drive it in its future.

17 years old when he was handed the keys. Dad lost him to stupidity. Its not what would let you get buy to save the car that should be your concern?

So ask yourself how safe do you feel in your tin can with all that power. I'll never forget the day I showed up at the accident seen to tow my old car. I knew my friends son was dead . I was in shock to see the car I street raced for several years. It looked much more compacted before they cut the passenger side door and roof off

Don't worry about the car worry about who is in the car. The 2 door HT darts crunch up the worst.

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It totally depends on what your planning on doing with your car when finished. If your plans are for just street driving you don’t need any frame stiffeners/connectors, however if your going to the track with sticky tires or slicks frame connectors will help. You really don’t need them until you have traction and the ability to actually twist…
 
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A56 said:
Not quite sure what you mean by factory cars, but my 340 cuda has all four of them (torque boxes). Agree that torque boxes and "heavy" torsion bars (1.03 or bigger) as well.
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not trying to be too technical here, by "factory car" I just meant some cars that came "stock"/ "off the line" / "off the lot" / "factory equipped" with torque boxes, from convertibles to small blocks to hemis, or even my car that came with none of the above. None of these cars ever came with frame connectors
 
Projectile Dart said:
not trying to be too technical here, by "factory car" I just meant some cars that came "stock"/ "off the line" / "off the lot" / "factory equipped" with torque boxes, from convertibles to small blocks to hemis, or even my car that came with none of the above. None of these cars ever came with frame connectors
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They didn't come with 550+ HP either. I'd do the torque boxes and weld-in frame connectors at a minimum. I would also make sure it has a good set of disc brakes in the front too.
 
Torque boxes and subframe connectors at the minimum.

Do you "need" them? Maybe not. But you don't want to crack the paint at the quarter seams either.

Depending on the use of the car you may want more. Like if you're going to set it up for aggressive street handling you'll want to look into doing more up front, like triangulation the shock towers and firewall (J bars or US Cartool braces) and stiffening the lower radiator support isn't a bad idea either. You can do it in different ways but the US Cartool kits identify all the spots that need to be reinforced.
 
cudamark said:
They didn't come with 550+ HP either. I'd do the torque boxes and weld-in frame connectors at a minimum. I would also make sure it has a good set of disc brakes in the front too.
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It doesn’t matter how much power your producing if you don’t have traction you don’t have body twist.
 
Oldiron440 said:
It doesn’t matter how much power your producing if you don’t have traction you don’t have body twist.
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Even the factory did torque boxes on the higher horsepower cars. And they were assuming skinny little bias ply tires. Even the all season radials guys like to run will hook twice as much horsepower as the factory planned for.
 
cudamark said:
They didn't come with 550+ HP either. I'd do the torque boxes and weld-in frame connectors at a minimum. I would also make sure it has a good set of disc brakes in the front too.
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I literally said to spring for both frame connectors and torque boxes...
 
This topic comes up pretty often. Most people forget very quickly when XV Motorsports was alive, 2005-2013, they were and still are the ONLY company to ever have the unibodies tested for stiffness on a surface plate. This was done at Multimatic in Canada. This was and still is unheard of. The bodies were tested as a baseline, then parts were tested and added as necessary to get a stiffness value on par with modern performance cars. At the end of the day, the parts that were developed were for B and E body cars, but the concept is the same. Frame connectors contoured to the floor, inner fender braces, under hood brace and radiator support is what it took. Having built several XV cars in house and afterwards, the parts work. It was proven at the time, torque boxes did not help neither did boxing the radiator support. I should also add, the radiator supports were 2x2 box, .125" and mandrel bent. The inner fender braces were also .125" wall tubing. I don't remember the tubing diameter.
 
Oldmanmopar said:
Frame connectors and a 10 point cage. The 111 inch longer dart flex quite a bit more then the 108 cars and that square roof doesn't prevent much flex. One other thing to consider is will a family member ever drive it in its future.

17 years old when he was handed the keys. Dad lost him to stupidity. Its not what would let you get buy to save the car that should be your concern?

So ask yourself how safe do you feel in your tin can with all that power. I'll never forget the day I showed up at the accident seen to tow my old car. I knew my friends son was dead . I was in shock to see the car I street raced for several years. It looked much more compacted before they cut the passenger side door and roof off

Don't worry about the car worry about who is in the car. The 2 door HT darts crunch up the worst.

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I thought I would get a disagree from the person responsible. No shame on what he did . 17 years old.
 
dicksmidlac said:
Helmet with an 8 point cage?
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As a general rule of thumb, if there’s any chance your head could hit any part of the roll cage in a crash you need a helmet with that cage for it to be much use to you. And remember if you’re not in a harness and your car ends up shiny side down you’re going to move a lot further out of your seat than you can replicate by just sitting in the seat.

Cages are VERY beneficial on the track. On the street, with no helmet and a regular shoulder and lap belt arrangement they aren’t nearly as useful. If you smash your head against the roll cage the rest of the compartment retaining its basic shape doesn’t help you much.
 
So, I have holes in my floorboards.
If I put in the subframe connectors and torque boxes would this compensate for the lack of structure in the floor?
(I just have sheets of metal pop riveted over the floor currently).
 
rr4406pak said:
So, I have holes in my floorboards.
If I put in the subframe connectors and torque boxes would this compensate for the lack of structure in the floor?
(I just have sheets of metal pop riveted over the floor currently).
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No!

These cars are unibodies. The floor is a significant part of the structural integrity of the chassis. This should be pretty obvious- in the factory design all that holds the middle of the car together is the roof, the floor and the rockers. While torque boxes and subframe connectors certainly help improve chassis rigidity, they won’t take the place of the floor.

Would it be better than just having a compromised floor? Probably. But if you’re going to take the time to weld in torque boxes and frame connectors you’d be better off starting out by welding up the floor. Patching the floor is no more difficult than adding torque boxes and subframe connectors. If you can add that stuff, fix the floor first.
 
72bluNblu said:
No!

These cars are unibodies. The floor is a significant part of the structural integrity of the chassis. This should be pretty obvious- in the factory design all that holds the middle of the car together is the roof, the floor and the rockers. While torque boxes and subframe connectors certainly help improve chassis rigidity, they won’t take the place of the floor.

Would it be better than just having a compromised floor? Probably. But if you’re going to take the time to weld in torque boxes and frame connectors you’d be better off starting out by welding up the floor. Patching the floor is no more difficult than adding torque boxes and subframe connectors. If you can add that stuff, fix the floor first.
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Kinda figured this would be the answer.
Just didn’t know how vital the floorboards were. Thanks.
*runs off to AMD to price out floor metal*
 
rr4406pak said:
Kinda figured this would be the answer.
Just didn’t know how vital the floorboards were. Thanks.
*runs off to AMD to price out floor metal*
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Yeah the short answer is almost all the sheetmetal on these cars is fairly vital. Some is obviously more important than others, but being a unibody if you start taking out too much sheetmetal things get flexy in a hurry. Heck, even from the factory they were pretty flexy. It wasn't as obvious back then because of the lousy traction the bias ply tires had. But even with your basic all season radials that most guys run now you can put more flex into them than the factory designed for. Hence lots of discussions about how to make the chassis stiffer.

I ran my Challenger around for 70k miles with holes in the floors (and other places I didn't know about). The car didn't fall apart, but, the chassis flex was really noticeable. I probably should have pulled it off the road long before I did. Did I die? No. Was it a good idea? Nope, not that either.
 
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