Boxed trailing arms

[DDS]

I've searched the archives and have found references to boxed trailing arms, but nothing conclusive.
Many seem to have done this mod, yet I could not find someone who recommends it. Any opinion that was expressed suggested that it is at best unnecessary, at worst detrimental. I'm in the process of installing GT type stiffening to the chassis, but am pausing at the trailing arms because I'm hesitant to add unsprung weight and am concerned about the heat.

1) Were the factory GTs equipped with boxed trailing arms?

2) Has anyone ever experienced a situation where this mod would have been of benefit?

3) If you've done it, any comments?

Many TIA as always.

Dave

[Joe Bob]

I did do it, recommend using a jig. The heat can warp the arms making it dificult to align afterwards. Not needed if using relatively stock HP motors...the GTs used the body kits but I'm no sure about the arms...

[Rich Hilgersom]

1)
A. Most likely not.
http://home.hiwaay.net/~jonlowe/brumo75.jpg
http://home.hiwaay.net/~jonlowe/brumo76.jpg
http://home.hiwaay.net/~jonlowe/brumo90.jpg

However, at this point finding a GT with them does not mean that it was in the "dealer kit"
http://home.hiwaay.net/~jonlowe/MVC026F.JPG
http://home.hiwaay.net/~jonlowe/MVC026F.JPG

-Rich Hilgersom

[JTB]

I have a friend who swears by it. His car is a 300 HP track car and he said that it made a huge difference. He did the chassis kit first and ran it for a year. Then he did the boxed arms for a year. With all of the extra stiffness in the arms and chassis, he ripped the trailing arm inboard mounting ears off of a rust free car. He had them rewelded and fabricated boxes for them as well. When I built my car, I did all of it at once. I did not have a jig for the arms, but the shop that welded them does very high quality work (nuclear submarine parts), so they knew how to keep them straight.

I made so many mods to my car at once, I can't say what change caused what part of the improvement.

As for the unsprung weight, remember that only 1/2 of the weight of the trailing arm and any metal you weld to it is unsprung. The other 1/2 is considered attached to the chassis and therefore sprung. Only the brakes, wheels, and tires are fully sprung.

Also remember - even if the original GT's did not box the arms, their tires were like rocks compared to today's sticky tires. We can put a lot more force through the suspension that an original GT ever did.

John

[Dave at Pelican Parts]

I've seen an interesting analysis that claims that the stiffening kits only eliminate ~10% of the flex in the whole trailing arm assembly. The kits do nothing for the tube where the pivot rod rides, and that appears (from simply analyzing the shapes & thicknesses) to be where a lot of the flex happens.

Most of the serious road-racers I know don't bother with boxing the arms. They simply replace the arms every couple of years. (And yes, serious means $$$!)

--DD