Slant Six Forum :: Chassis Stiffening

After putting extra large subframe connectors in my '66 Dart I noticed a lot of flex forward of the firewall. If you visualize the chassis as pair of springs with the firewall as a bulkhead between them it is easy to see that I made the rear spring very strong, but did nothing for the front spring. This is a real problem for the front suspension and for handling. To reduce that flex I would have needed to do work forward of the firewall and the US Car Tool kit looks like a very good option. It's amazing how much the front end flexes and twists when you put on sticky tires and suspension to match.

Author:	SpaceFrank [ Tue Jul 14, 2015 4:15 pm ]
Post subject:	Chassis Stiffening
I posted this in a previous thread about body reinforcement, but that thread had kinda already gone off the rails. Josh Skinner posted the following at some point early in the thread, and I'm hoping to get some more input on this front for stiffening the LeMons Dart. Quote: After putting extra large subframe connectors in my '66 Dart I noticed a lot of flex forward of the firewall. If you visualize the chassis as pair of springs with the firewall as a bulkhead between them it is easy to see that I made the rear spring very strong, but did nothing for the front spring. This is a real problem for the front suspension and for handling. To reduce that flex I would have needed to do work forward of the firewall and the US Car Tool kit looks like a very good option. It's amazing how much the front end flexes and twists when you put on sticky tires and suspension to match. Josh, what work would you recommend forward of the firewall? One of the major jobs we've got planned for the Race Dart is to tie the subframes together. I actually bought a single US Car Tool subframe connector for the passenger side, but the driver side connector we have to build custom due to the dropped floor. We've got a DOM six-point halo-style roll cage in the car. Our A-pillars currently land directly on top of the rear member of the front subframe, and our backstays land on top of the rear frame rails, but the spreader plates are only welded to the floor. The B-pillars are also gusseted to the rockers with 1/8" plate. I'd basically like to solidly connect every leg of the cage to a frame element. We also had to patch the footwells in the front, and I don't think the floor is actually solidly connected to the front subframe under the patches. I'm planning to go under the car and weld the subframes to the floor everywhere I can. We did add triangular roll cage elements between the A-pillars and the firewall to give better side-impact foot protection, since our A-pillars are so far back. I'm guessing I could run some bars from the opposite side of where those hit the firewall up to some point on the front suspension? Maybe through-bolt the spreader plates through the firewall?

Author:	Reed [ Tue Jul 14, 2015 4:51 pm ]
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Dan posted this link a while back: http://store.uscartool.com/70-75-a-body ... g-kit.html Looks like a good deal.

Author:	Danarchy [ Tue Jul 14, 2015 7:33 pm ]
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1964 Dodge Dart Might as well build a tube frame and put a Dart body on it!

Author:	Dart270 [ Wed Jul 15, 2015 6:14 am ]
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Most people run front engine bay bars from the downbars of your current cage, starting about at the lower-mid level of the dash, angling forward and then downward to land near the front of the front frame rails. You can make these tubes pass over and attach to the shock tower top. Also have them pass through and weld to the firewall. This will go a long way to solidifying the front end flex that Josh was discussing. You can also weld a bar between the front frame rails up by the radiator, maybe a U-shaped bar that serves as a rad support. Somehow, my 64 Dart is very solid and rigid, with no cage, subframe conns or anything. Must help that it is rust free and with all susp/chassis/steer/K bolts overtightened. Note I have not run race tires on it, but have run (2007) autoX tires and have pretty sticky 300 treadwear Goodyear Eagle F1 Asymmetric 2s now. I will probably do some stiffening in the future. I think with fatter autoX tires, I would have been 3rd in the Carlisle autoX instead of 5th, and just behind the Reilly susp V8 Duster. Lou

Author:	Joshie225 [ Wed Jul 15, 2015 8:06 pm ]
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Yes, the cage extending through the firewall helps front end flex a lot. It helps so much that it's illegal in most club racing classes. Having an X at the top of the cage helps torsional stiffness. Most any time you can triangulate a square you'll gain stiffness. This is why engine compartment and under chassis X braces are popular.

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Author:	Sam Powell [ Sat Aug 01, 2015 6:05 am ]
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I always thought the upper control arm tabs look like a weakness. It seems like it would help to get some triangle bracing to them in some way, but have not looked at it enough to know where, or how you would place them. The sagging of these was what the problem solver UCA bushings are supposed to address. Sam

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