At what point should I reinforce the unibody

[Hemmit]

I have a 73 charger, 440, 9 1/4 rear end(unknown internals). Going for 550 Ish horsepower/torque. What do I need to reinforce on the frame/unibody, or do I. Was thinking of reinforcing lower control arms, And frame connectors. Anything else? Want it for driving and the occasional unleash. Thanks

 

[71Beeper]

Frame connectors is a must, especially at that horsepower level.
If you can weld and do minor fabrication, them make them yourself from 3" x 2" rectangular tubing or buy the complete chassis stiffening kit from US cartool.
Torque boxes in the front and back should also be installed.

 

[diesel_lv]

https://www.hotrod.com/articles/mopars-big-power-need-subframe-connectors-heres/amp/

 

[Paul_G]

I dont think your going to find many kits for the 73. First year for the isolated K frame. At least I have not found any. If you do please post them here.

If you stick with street tires that do not grip well you wont really have issues with chassis stiffness. The tires will break traction and spin before frame twisting will occur. If you use a good tire that gets traction, then definitely need to reinforce the chassis.

 

[kiwigtx]

Reinforcing the unibody should take place before this happens...

 

[Paul_G]

One more thing. If you can not cut and weld to fabricate your own frame connectors, find a custom shop that can. Spinning the tires at will is fun, but then it gets old.

 

[440 Charger]

Never a bad thing from what I have seen to make things stronger than they need to be.

 

[Montclaire]

The front subframe on the 73+ cars is pretty stout. You should go with solid k-frame biscuits at the HP level. I would also use solid spacers for the torsion cross member. Rear axle mounts can be swapped to the earlier style.

 

[Paul_G]

The front subframe on the 73+ cars is pretty stout. You should go with solid k-frame biscuits at the HP level. I would also use solid spacers for the torsion cross member. Rear axle mounts can be swapped to the earlier style.

I used poly sub frame mounts, torsion bar mounts, and rear axle isolators. Not as good as solid, but they firmed it up a lot.

 

[MoparLeo]

Unit body construction was intended to make manufacturing less costly. These cars were just spot welded together. 40-50 years later these welds work loose on a slant six car. Always a good idea to stiffen up the entire car even if it is just by going back over some of the stress areas and rewelding with a M.I.G or T.I.G or even an old Arc welder. You would be surprised at the cracks and loose welds on these cars. Why do you think they sell stiffening kits ?

 

[moparedtn]

Why do you think they sell stiffening kits ?

I'll go out on a limb on this one and answer "....for a profit?"

In all seriousness, as always your advice comes from a source of wisdom, sir.

 

[71Beeper]

Front k-member stiffening kit from Firm Feel.

I used these on a 1976 Volare Road runner I had back in the day.
Made a huge improvement over the original rubber isolators.

 

[Nacho-RT74]

73 and lates get the T bars cross member in the middle. Is not that easy like 72 and lates. That's something to check.

IMHO, a good set of torque boxes could be more than enough for a HiPo street car. That was the factory setup even on Hemi convertibles and 4 speeds. Now if you will gonna race it, that could be a diff story, but still will depends on how "profesionally" will you race... or just for a quite often fun

 

[440 Charger]

I have been fabing making sure to tie in the front and rear sub frames it has helped a lot.

 

[440 Charger]

Front k-member stiffening kit from Firm Feel.
View attachment 1060001

I used these on a 1976 Volare Road runner I had back in the day.
Made a huge improvement over the original rubber isolators.

That looks like a great idea will look into it thank you for the info.

 

[440 Charger]

Reinforcing the unibody should take place before this happens...

View attachment 1059695

Lol that would suck.

 

[71Beeper]

With frame connectors and torque boxes in place, it should look like this....

 

[Paul_G]

On the 73 and later the torsion bars pass through the crossmember and mount to the isolated mount behind the crossmember. This is a pic of the underside of my 73. You can see how the isolated mount will be in the way of the frame connector. It will take a little work to get the frame connector around the isolator.

 

[Nacho-RT74]

As mentioned previouslly... hence the reason why most of aftermarket parts manufecturers don't offer connectors for 73 and lates...

Could it be made diagonally? Maybe, but the emergency brake lines and parts will be in the middle too

 

[71SandbugCharger]

There are many posts on this. This one addresses the kit always seen in magazines.

https://www.forbbodiesonly.com/moparforum/threads/b-body-mopar-chassis-stiffening-kit.119901/

https://store.uscartool.com/Chassis-Stiffening-Kits_c_46.html