Chassis stiffening.

[torqueaddict]

For a normal street driven car is chassis stiffening something that should be considered? Is it a need to have upgrade and what company makes the best? Thanks for the help guys.

[HP2]

Definetly worth it on anything. These chassis are 40 year old. There were not designed as the most rigid set up way back when and the years have not been kind to most of them. Stiffening kits will go a long way towards eliminating squeaks, creaks, and rattles. On top of that, they will ensure panel gaps are held in alignment, that the suspension reacts the way it is supposed, and all your power is getting to the ground. The only reason not use to chassis stiffening is on a 100 point, concourse restoration. Other wise it is a benefit.

[ChallengerHK]

Is there a point of diminishing returns? Are some parts more valuable than others for chassis stiffening?

I'm thinking of two things. Geometrically speaking, subframe connectors seem to have more effect on straight-line launches, for instance, while torque boxes seem to do more for torsional rigidity.

the other thing I'm thinking about is the XV fire-wall to inner fender braces. I may be wrong (tell me if I am) but I can't see how those alone are going to add much. They seem to need something to tie the two sides together in order to really provide a lot of benefit.

[Topcat]

I've noticed over the years cars that were upgraded HP and torque and had body filler done (because they were originally vinyl topped)...at the sail panel area develop cracks.

Right where the roof meets the quarter panel.
After years of hard usage, cracks would appear on the seam.

Mine was a perfect example of this happening. Once a 318 A/T. Converted to a 4 speed limited slip. About 5 years later, cracks appeared mainly on the D/S sail panel area. Obviously this was a result of body fatigue and flex. Add to that; too thick a filler in the area didn't help either.

Mine is leaded and the frame areas re-inforced with sub frame connectors.
Doubt I'll have that happen again!

[HP2]

I've never see any analysis of sub frame connectors vs torque boxes for rigidity. Certainly either would help considerably in stiffening things up. My car will actually have both, but my subframe connectors will be Xed into the torque boxes instead of longitudaly mounted.

The best analysis on support that is documented and readily available on the web was performed by XV. They do say that as a package, their units improve rigidity considerably (I forget the exact amount, but it is substantial) with a minimal amount of increased weight. Yes, there becomes a point of dimenishing returns on a street car. This is why the XV kit is actually pretty minimal.

Their researched showed that the front third of the car, the engine bay, was the most prone to "diamonding" when the suspension moved. The front structure was flexing and allowing up to an inch of movement in some areas. This is where the lower radiator support and fenderwell braces tie it all together. They also offer a "monte carlo" bar which further ties in the inner fenders to the firewall to create the tie in between the pieces.

[Chryco Psycho]

the front fenderwell braces should help by tieing in the shock mount & triangulating back to the firewall area

[Road_Runner]

I'm looking at the XV "Monte Carlo" bars similar to what I installed in my Mustang fastback many years ago.  These tie the inner fenderwells to the firewall and eachother and really tighten up the front end of old Mustangs.  Other than subframe connectors I don't want to permanently modify the Barracuda.  I've seen some negative feedback on the connectors that conform to the bottom of the floorpan, but I'd like to use these and hide them under normal undercoating where it looks stock.  Anybody just use one of the underhood MC bars and maybe subframe connectors and can share how they helped?

Thanks, Jim

[Chryco Psycho]

IMO the MC bars do nothing in a Mopar , the suspension is unique in a Mopar by using a T bar along the frame rail so tying in the shock towers has minimal effect

[ntstlgl1970]

I did the XV radiator brace, shock tower to firewall brace and their subframe connectors, I would like to add some torque boxes in the future. I can't comment on individual parts for effectiveness, but I can place the jack under the frame just forward of the trans/torsion bar crossmember and it will lift the whole side (both wheels I mean) off the ground, where before it would only lift the front tire up - So in my opinion it does help. I agree with CP on the firewall to shock tower brace, since the weight loads the torsion bar crossmember, not the shock tower like a mustang. Looking at the roll cage on the original T/A AAR race cars, they didn't have one though they did have something that tied into the rollcage.

[mopar12372]

i believe that if a cross bar was added in front of the radiator support then install frame connectors and torque boxes strengthen the shock mount  struts  . with out a cage that should be enough for a car to handle .

[Road_Runner]

Thanks guys, I'll skip the MC bar and just start with the frame rail connectors and go from there.

Later, Jim

[willhaven]

I did the XV stiffening kit but skipped the engine compartment brace. It wouldn't clear the six pack.

In 2006 I watched the Dream Car Garage series where they walked through the development of their suspension. They used a 4 post hydraulic rig to pinpoint where they flexed and devised a plan to fix it. The results looked nice and I was sold.

I was tempted to get their suspension, but I'm not sure if I really need it. And after hearing some horror stories and waiting on parts from XV myself, I'd probably go Reilly Alterktion in the front and Heidt's IRS in the rear instead of doing the XV kit. IF I even decide to go there in the future. The Hotchkis setup looks pretty solid as it is.

[brads70]

I just have the torque boxes and sub frame conectors on mine and when I place the jack on the t-bar cross member the whole side of the car lifts up too. ( front and rear) . Wanna see something scary.... jack up the car and put it on 4 jack stands and watch how much the front end sags till the jack is free of the car!( when jack is on the k-frame)  That's what I'd like to improve on mine?
The front end moves 1 1/2" to 2" easy before the front jack stands can move. All that "flexing" can't be good I can't imagine how much a vert would flex?

[mojavered]

Brad, can you elaborate a little on this flex you have?  When you see this movement, where is it at?  Where are you lifting from?

[HP2]

I've seen that.

Put two jack stands under the  sub-frame by the torsion bar cross member. Put two more under the subframe bu the front leaf spring hanger. The ends of the car will droop. It comes from a thousand little spot welds through out the sheet metal structure.

This front end drop is what the XV kit improves. They tie the upper shock mount area into the firewall to reduce drop and the square radiator supports limits twist. You certainly can get more involved than that, but their design provides a large increase in rigidity with a minimal amount of intrusion.

In cage construction, you'll notice the good builders have a fair amount of triangulation between the main cage area and the suspension mounting points in the nose. Everything in front of that is pretty tame to provide some crush area for impact.