Here's a simple qestion: I am in process of redoing my 89 GTA. I have the engine out and I am redoing the the underside of the car at this time. I am changing bushings,springs,tracking bar, ball joints ,shocks and about everything else. Do I need the wieght of the engine in the car to weld sub frame connectors in?? As soon as the new spohns are ready I will get those. I really want to put the engine in next to last. The body work will be last. It would be nice to have the SFC in before the headers and pipes are in the way.

I'm pretty sure you would want the engine in when doing that. Or at least simulate the weight of the engine. If you were to install them with the engine out and less weight on the front, when you would put the engine back in the change it weight would put forces against the SFCs in the position they are welding in. I believe the point is to weld them with the weight of the car to keep everything tight in that instant. Not a lighter instance. Sorry if that's a bad explanation. I'm tired.

no you want the suspension completely loaded when you weld in your subframes

Do new car manufacturing companies always weld the frames with the engines in?? What about custom race chassis builders? I am not sure it matters. Sub frame connectors limit the twisting of the car as a primary purpose. I think that twisting about the front to rear axis of the car will be minimal when the car is at rest, loaded or not. Opinions?