I have no idea but ive heard it cracks the shock towers on our cars ?????
I think you're combining 2 common alleged complaints in one statement.
One complaint that I've not seen documented, but I don't argue it, is that the aftermarket tubular K members crack and flex under severe road race/ autocross use. So strong is that complaint that most makers offer heavily gusseted chrome moly versions for road race use. Like I said I've not seen evidence of that happening but then again driving my car on a slalom course, running over orange cones is not appealing enough to me that I looked for evidence.
Secondly, and documented enough that I've seen threads and pictures, is that using coil overs on 3rd gens does indeed crack the upper strut mount.
The 3rd gen is designed to carry it's front end weight via coil spring positioned between the lower control arm and the factory K member's upper spring perch. Never really requiring the upper strut mount to carry much weight other than the forces generated by bounce control .
The job of struts on 3rd gens is to act as the upper control arm pivot/ ball joint and provide bounce control that the traditional shock absorber would.
The relatively flimsy upper strut mount is a sheet metal hat(if you will) tacked to the metal inner fender well. And it is positioned further outboard the "lever" of the original coil springs position.
Now many people convert to coil overs with no problems at all, but I suspect these examples are casually driven and not punished by daily driving, autocross or hard launches.
The sheer size and construction of the factory K member clearly seem to prove it is stronger than a compact tubular design, but it's sheer size and construction make it very difficult to add turbo exhaust plumbing and make engine swaps a tight fit.
Aftermarket K members are mostly sold with the traditional upper spring perch to allow the use of the original coil spring design and location. And they've been around long enough, and sold and used often enough that all issues have been addressed.
Now the 4th gen F cars are designed for a coil spring over strut and the upper is clearly strong enough and engineered to handle it as a weight carrying location.
