Comment:

Richard Guy

The car looks like it’s entirely made from square tubing.

Round tubing is as strong structurally and lighter, probably why it gained favor. 

Square tubes have, obviously, four sharp bends, each a weak link in the material.  A round tube has no bends, making it stronger.  Another consideration is DOM (drawn over mandrel) round tubing which has no welded seams. 

The weight reduction can be understood if you look in cross-section at a one and one-half inch square tube and round tube.  Each can carry the same load but looking at the cross section you can see less material is used to make the round tube thus saving weight.

I am not sure of the exact history but I believe DOM technology was perfected during the space race and became economical enough for civilian use around the time of this picture.  Up until that time even round tubing began as a piece of flat stock which was rolled into a circle and welded at the seam. 

All the square tubing I have used recently has two welds on opposite sides.  In other words two U-channels are welded together to make a tube. Welders will argue that a weld has a 70k psi strength, the base metal only 50k, so the weld is stronger.  But all welds have a HAZ (heat affected zone) between the weld bead and the base metal.  A good weld will transition the HAZ with no problem but a defective weld could easily result in the HAZ being weaker than the weld bead and/or base metal.  So if the machine that welds the seams on the tubing is out of adjustment the strength could be compromised.  Unless every piece is inspected with X-rays, sonic testing, or other means the naked eye will not detect any such weakness. 

So add up all these factors and round DOM tubing becomes the best in a direct comparison.  The only drawback is the "bird mouth" joints and welding.  The joints are difficult to get a good fit unless you have proper equipment and any welder will tell you welding round tubing will test you skill and patience. 

This is the extent of my knowledge as an amateur fabricator.  I am sure a metallurgist can provide a better and more complete explanation.

As far as rules, if I recall when jig built chassis debuted the rules required square tubing 2X4 tubing to level the playing field with those still running Chevy frames.  The square tuning also looked more "stock" unlike the "bugs" they ran at Williams Grove.   

For what it is worth.

Terry Fick

I have a photo of what I'm pretty sure is the same car but painted white. It was taken by me when I was about 10 years old at a "run what ya brung" early spring show at Stafford Springs. It has Cagle lined up with a bunch of super modifieds. If I remember correctly, he won his heat and managed a top five driving a dirt car against the supers! Boy, did I love those days of wild racin'.