80s g-body frame brace and suspension question

[silvermonte]

I notched the frame on my 80s cutlass to allow for some wider tires. While I was at it I braced up all the weaker points in the frame and also boxed in all the open areas. The area that I worried the most about was over the rear axle. I took out a fairly large chunk of metal when I did the notch and wanted to brace it up to minimize frame flex. I did not have the axle in when I put in the pipe for the bracing and at the time I thought I had plenty of room for suspension movement. After putting the axle back in I have alot less then what I think I need and will have to redo my work.

I have 2.5" of clearance till the upper arms hit the pipes. In the very near future I will be swapping to coil overs and I want my car to sit as low as I can reasonably get it. My thought is when the lower arms are level is probably the best. So my question is how much movement will the axle have with coilovers, and with the current coil spring set up. Im not looking for an exact number but just a general number so I can make adjustments right now.
https://static1.pt-content.com/images/pt/2014/01/001_zps79e203bb-1.jpg (http://s213.photobucket.com/user/silvermonte/media/001_zps79e203bb.jpg.html)

When I put the pipes in I figured this was a good set up to brace the frame from flex. I do not have a degree or anything close to having any real knowledge of the subject. Since I will be redoing it I would like some opinions on what I should do to better brace it. After the coilovers are installed, and way down the road I may put in a watts link, but that will depend on budget and if there is a need for it.
https://static1.pt-content.com/images/pt/2014/01/005_zps82201884-1.jpg (http://s213.photobucket.com/user/silvermonte/media/005_zps82201884.jpg.html)

[SSLance]

Take the springs back out and cycle the suspension until the bump stops hit the frame, you need enough clearance for it to travel at least that far.

The suspension travel won't change when you put coil overs on it, they just make it easier to set your ride height. Looks like if you just took the fronts of those tubes and moved them out away from the Upper control arms that would work.

[silvermonte]

Looks like if you just took the fronts of those tubes and moved them out away from the Upper control arms that would work.

That is what Im planning on doing unless someone knows that it wont provide as much support as a different set of angles. I wondered if I should put the "V" of the tubes on the factory portion of the frame and then angle them to the bar that I put in, but I really didnt think it matter all the much.

[SSLance]

The tube you put in is primarily to support the side to side movement of the notched portion of the frame rails correct? It might do that all on it's own without any triangulation tubes attached to it. The triangulation tubes just help to keep the whole frame most stiff and straight. It is probably more crucial that they are there than exactly where they are situated, but I'm no engineer either.

[jlcustomz]

Id say exact location of triangulation bars is not as important as having a little more angle on them to help the side to side stiffening.

[Marcus SC&C]

Miles, what you`ve done is certainly better than nothing but I`m sure you`re going to run the housing "ears" into the braces in bump. I`d splay them outward more at the front to the juncture of the cross member and shock/spring mounts which will also improve triangulation and help prevent lateral deflection of the sectioned rails. Remember the added cross member itself does almost nothing in this regard it just gives you a place to mount the triangulating members that do. If you wanted to do a little more value added you could add two shorter braces from the round tube cross member to the shock mounting area. Place the points on the cross member to allow for tailpipe clearance but get a good diagonal angle on them in plan view. These should also give a little triangulation of that shock mount in side view to help reduce vertical deflection.

A coil over conversion "should" have as much travel as you had stock (some don`t). If you want to get the best performance out of your car you may need to resist the urge to adjust ride height to the "lowest/coolest" height. On this platform the rear roll center (RC) is dictated by the convergence point of the upper trailing arms. It`s already an extremely high roll center and because of the fact that the RC is floating is space just above the diff cover it goes UP even higher when the suspension is lowered (this is opposite of how the front of the car works, a bad thing). With the RC so high to begin with we very quickly end up with the RC higher than the center of gravity (CG), inverting the moment arm between them. Now the front and rear of the car are completely out of sync and the car becomes much more unpredictable, harder to drive. You also run into the very real possibility of running out of bump travel. When this occurs, at very least the ride quality will be poor. At worst the car will tend to snap over steer at the worst times, going out of control.
The frame boxing was a great idea and you`re on the right track so far. Nice work.