Sub frame connectors - overkill?

I agree... plus if you noticed a few past posts by members, there are some that show how well the body keeps straight by how they balanced their body on a lift.

I have lifted my body at its balanced center point to see how it flexes as for the door fitment to the door frame. Mind you this body is unrestored with high milage with 30 years of use as a daily driver.

The doors close and keep proper alignment with 1/16 deviation in corner height. Which is pretty darn good IMO. Though some may find it not so for their car, due to rust or door hinge issues.

Though, if racing on autocross, I would beef up the frame by utilizing some intergral roll cage tube steel reinforcements at the corners along with a custom cross bar to bolt at the steering box holes on both left and right sides. Hardly any welding if any to the fron frame as the front section is drop in and bolts to the firewall and roll cage in the car.

The key is to stablize the corners not over do on frame to compensate for corner twist. Seems that the frame and body structure is good at flex in the up and down axis. The suspension and lateral axis is weak.

My 1970 Javelin lead a life of being driven pretty hard and the unibody was tweaked and needed straightening on a frame machine. That being said, for the cost of subframe connectors and the added strength the provide I would think it is a no brainer. $200 for subframe connectors is cheaper than time on a frame machine. However, if you are a daily driver and not putting a ton of power to the rear wheels (with traction) then the body will not twist bad enough to cause a problem with a stock setup.

My Hemi/ Javelin recently got hit in the rear. The impact was hard enough to buckle the quarter panel into the door that impacted the back edge of the fender. It only chipped the paint on the door and fender. I would like to think that the sub frame connectors and mods I made to the rear frame rails in order to mini tub this car helped save it from further damage to the unit body. While unit bodies are usually pretty strong, most are designed to fold up under impact of a crash to lessen the blow to the occupants. I still have to replace the bumper and tail light panel as well as pull the quarter back some but I don't believe I have any serious frame damage.

71hornet6 wrote: I am guessing there are levels to upgrading the suspension Level one: replace all the bushings and shocks Level 2/3: replace rear springs if needed etc...

Not bad advice -- but the key is 400+ hp.  Under that and you should have no issues. That's not a design flaw -- few cars are designed with 400+ hp in mind. If it is, it will have additional body support. Take the SC/Rambler, for example. AMC knew the body would flex even with the 343 hi-po engine (that's why they only sold a few Rogues in 67 with the 343, then discontinued the option). The SC/Rambler coupe bodies have all the convertible bracing in them, making them a good bit stiffer. They will still flex a little when prepped for serious drag racing.