I'm going to disagree with the mounting points and style of the bar.

First we have to agree about how the chassis deflects as you go into a turn. I’m sure we’ll both agree that it will twist and that the strut towers move inward towards each other.

So the job of the strut bar is to prevent the twisting and the towers from deflecting inward.

A horizontal bar along the same direction as the force will do nothing against the twisting. I’m sure at some point or another most of us have hammered together 4 pieces of wood to create a frame and noticed how easy it was to deflect it. To prevent twisting the structure needs to be triangulated. Ideally there would be a bar going from the top of one tower to the bottom of the other, but there’s an engine in the way so you can’t do that. So attaching to the firewall is your best bet to accomplish this. The firewall is made of thin sheet metal, yet so is the rest of the car and it manages to stand. I haven’t cross-sectioned an eclipse, but most cars have a bulkhead running along the cowl. I’m pretty sure the upper firewall can carry a load.

To prevent the towers from deflecting inward all you need is a beefy bar across it. But you’re better off with a pinned structure like the cheap ebay bar than the solid neuspeed bar. A pinned structural member only carries a load along its axis. It will not carry a flexural moment like a solid bar would. So a solid bar has to be rigid in flexure which means it has to have a large height (why an I-beam works). A pinned bar only has to prevent buckling which even for a small skinny bar is a very large load.

As far as mounting points on the towers I don’t think it matters much because I don’t believe local deflection of the towers is significant. But if you don’t want to make that assumption then mounting it to the upper A-arm bolts is probably not the place. Again since pinned members carry loads only along their axis the upper A-rams have a tendency to twist the bolts. And both the left and right upper arms will be stressed in the same direction and both bolts will twist; linking them together will do nothing to prevent this twisting.

-J