This Is On A 1984 Z28

 

That's a "Wonder Bar", or wander bar, depending on who you check with.

It's a brace to tie the front frame rails together. Helps prevent flexing of the driver side rail in the area the steering gear box mounts. With a fast ratio box, the frame is prone to cracking in that area.

There are originals, and aftermarket. I didn't "think" those came along until the IROC cars, but I'll let someone more well versed in that address that issue.

 

Yep, that's a steering brace or "Wonder Bar". Looks like an aftermarket add on.