An 80mph collision will not kill you. It can hurt you, but the G force alone will not kill you. I know someone who survived an estimated 120mph impact.
He was driving on an interstate and an elderly woman fell asleep at the wheel and came at him head on. He corrected by crossing over to the other side of the highway and slowing down to about 50mph from the 70 that he was going. When the woman woke up seconds later, she corrected and hit him head on. I’m not sure what the other woman was driving, but he was driving a fullsize 1980’s ford F-150.
I’m sure that her age and lighter vehicle was what killed her, but my only point is that collisions at ranges around 100mph will not kill you out of G force alone. If that were true, dragster drivers and airforce pilots would die. You might pass out, but that amount of G force alone will not kill someone in normal health.
The 80mph collision that I saw was a relatively direct hit, but not all of the inertia was stopped. He did spin and come to a sliding stop. It knocked him out for a brief moment, but he did get up and walk away from it.
Older vehicles aren’t safer than newer ones. I’m just saying that any vehicle prepped with a cage will hold up better and be safer in an accident against the same with a modern SRS system.
I’ve used mandrel benders and have built cages that are NHRA approved. Most are made from chromoly, which is slightly lighter than steel and stronger as well as having better damage resistance characteristics (will not bend as much), but NHRA as well as many other associations require the welds be inspected and corrected after a certain amount of usage, due to the vehicle twisting under engine torsion.
But for a street car, it doesn’t matter, because you aren’t emitting thousands of foot pounds of torque to the cage to weaken welds. You add about 200lbs at most in a full multi-point cage when using mild steel.
NHRA requires a cage made of .125" thick mild steel, or .083" chromoly. This is because chromoly is twice as strong as mild steel.
Most full multi point cages use about 95 feet (roughly 30M) of .125" thick 1 5/8" steel tubing, which weighs in at approximately just under 2lbs (1.97lbs) per foot, plus any flat stock, welds, etc. When you do the math of a full cage, even at 100 feet of tubing used, that’s 197lbs made of heavy mild steel. and this would be a full racing, multi point cage. A basic six point cage would weigh significantly less (maybe 1/2 to 1/3 of the weight) and do just fine under higher speed indirect collisions and certainly almost anything you could dish out at 40mph or under. Even if it were made out of mild steel. Going to chromoly, because of the thinner material requirements, would come in at about 140lbs for a full racing 12 point cage, but mild steel is easier to work with.
Between the weight savings from fewer electrical devices (I’m willing to bet that depending on the vehicle, you are looking at 600-1000lbs average of electrical junk) and losing the heavy powerplant, the gains made in weight from a cage are insignificant to it’s benefits. If they weren’t, you wouldn’t see race car drivers use them, where every ounce matters, literally.
That Volvo would be such a sweet car to convert. Most older Volvos don’t weigh that much. The newer ones weigh upward of some full size trucks or more.