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Hands down - a full frame from Morrison or other vendors would be stronger and more rigid. These frames have triangulated braces built into them that a frame-tied unibody would not have. Even after subframe connectors have been added, you'd still have a front sub that is merely bolted onto the Nova unibody. No way this even comes close to a well designed full frame.
 

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novanutcase said:
In the full frame I wouldn't be using a cage.
if you were to NOT use a full frame, you'd put frame connecters and a cage in it? if so, that would be WAY stiffer than just a standard frame....no matter if its from GM or morrison, a cage is much stiffer.....example. when you jack up any full chassis car(no cage), lets say a 78 malibu, from the front corner, the front tire will come up. when u jack up my brothers firebird with a cage(unibody) from the front corner, the whole side comes up(both front and rear tires)......my brothers firebird sits on 3, probably even 2 jackstands, and it has frame connecters and a 10pt. cage...
 

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This has got to be for road racing? You are correct in persuing chassis stiffness since the chassis is the anchor point for suspension loads.
Maximizing stiffness while minimizing weight is all in the design. The lightest designs are custom built, triangulated tube chassis with the body panels hung on.
Taking a production car and doing this leaves little of the original car.
The Early Chevy II is a very flexible car and not even close to modern stiffness bench marks (Like a Z06). Anything you do will only improve it but adding weight is counter productive to performance. It all depends on the rules and how much you have to spend.

There is a lot you can do but You need to know scientifically if what you do helps or just adds weight. Getting numerical data on stiffness is a lot of work. Here's what we do:
You have to secure the body to a heavy surface plate (not something a person typically has in a garage.) The rear suspension mounting points are restrained and a long bar is attached to the front suspension. Weights are added which is mulitplied by the length of the arm.
The base line degrees of twist is measured. You'll be shocked at how much an old Unibody car like a Nova twists.
Then the roll cage is built in a manner so that the critical areas are supported and the suspension force is transferred into the cage. This is the tricky part. It's like building a suspension bridge. Maximizing strength and ridigity and minimizing weight is tricky. Most commercial drag cages are just for safety and don't address chassis stiffness. I wouldn't select a drag roll bar for a road racer if I was planning on winning.

The old story about Colin Champman of Lotus could make a car that was so light and yet stiff that if you took any one tube out of the design it would fall apart.
 
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