boxing 84-87 front LCA's?

[ericjon262]

Title pretty much says it all... Any thoughts on boxing the front LCA's on an early car? I've seen it done on some of the older muscle cars before, it's pretty straightforward process, I have the material...

Pros-

Increased rigidity of the LCA

Cons-

Heavier LCA.
Possible increased NVH both from less flex, and possible wind noise.

Thoughts?

[FieroWanaBe1]

In my opinion the front lowers have a lot of steel in them relative to the uppers and rear lowers.

Not sure if there is as much gain to be had vs the uppers or rear lowers.

[ericjon262]

In my opinion the front lowers have a lot of steel in them relative to the uppers and rear lowers.

Not sure if there is as much gain to be had vs the uppers or rear lowers.

I was thinking the same, I think most of the rigidity comes from the heavy spring plate in the middle of the arm, it it were removed to install coilovers, I think then boxing would make a difference.

[pmbrunelle]

The spring plate is just held on with a few rivets IIRC, so it cannot contribute much the strength/stiffness of the arm below.

The front LCA was built pretty beef because the spring is pushing on it near the middle.

The other control arms only have loads applied to them though the ball joints and though the bushings, so they don't need to be as beefy.

Future sandblast+repaint jobs will be compromised with boxing in, and the potential to collect water/mud/rust?

I would probably try to do some rough estimation (by calculation) to see how much the ball joint moves (or whatever other metric you wish to improve), determine if there's room for improvement, and then decide if it's worth to box in the arm.

Is there a way you could draw the LCA in OnShape, and then get it into some finite element analysis program? Then compare with/without boxing in?

[ericjon262]

The spring plate is just held on with a few rivets IIRC, so it cannot contribute much the strength/stiffness of the arm below.

The front LCA was built pretty beef because the spring is pushing on it near the middle.

The other control arms only have loads applied to them though the ball joints and though the bushings, so they don't need to be as beefy.

Future sandblast+repaint jobs will be compromised with boxing in, and the potential to collect water/mud/rust?

I would probably try to do some rough estimation (by calculation) to see how much the ball joint moves (or whatever other metric you wish to improve), determine if there's room for improvement, and then decide if it's worth to box in the arm.

Is there a way you could draw the LCA in OnShape, and then get it into some finite element analysis program? Then compare with/without boxing in?

I'm not as worried about future sandblasting/cleaning, anything like that would be incorporated with the boxing, and hopefully not necessary for a REALLY long time.

on the spring plate, it is fairly heavy, and while only connected by a few rivets, it does tie the lateral member, to the diagonal member, which could have an effect.

Drawing the arm in a design program and performing an analysis is an idea. not sure I'm that invested in the idea as a whole though.

[The Dark Side of Will]

I think you're better off using the design and fab effort that would go into boxing the production arms toward building something better from scratch.

The front lower arms for both early and '88 cars are heavy because they have bending loads in normal use. The UCAs and rear control arms only have tension/compression loads, which means they can be MUCH lighter and still do their jobs just fine.

In particular, boxing does almost nothing for a structure loaded in tension unless you go to length to tie the ends of the added structure into the original structure as close to the load application points as possible. Boxing can help a channel structure resist buckling, and thus can help it withstand compressive loads, but... I've never heard of anyone folding up a control arm or lateral link just from running slicks, soo... Why bother?

[ericjon262]

Thanks for the responses, I kinda figured it wouldn't really be necessary, but also figured it wouldn't take a ton of effort to execute either. I'm just going to throw the stock arms in with the spherical bearings, and when the car is ready for the next step, we'll go from there.