OpInstall solid body bushings when you do this.
Exactly. One way to think about it. From the factory, the subframe and body are only attached by a few bolts. Essentially they can flex relative to each other as two separate parts on the mounts (were talking small movements). The subframe and everything attached to it probably weigh close to a half a ton. The body, rear suspension and everything weigh another ton or more. As you go down the road vibration inputs come from the engine, trans, and the road surfaces (through the tires) exciting the two different masses at a different rates, but again it's not tied together rigidly.Absolutely put them in, I have the DSE weld in connectors with their solid mounts. Poly mounts will probably work but read the info on the connectors without doing a solid mounts and you can decide. Biggest difference for the money I have done to the car hands down.
Camaro Body Bushings - Resto Shop
Competition Engineering bolt in. Had jack stands up front and taking them out jacked up one side, removed the jack stand from drivers side, released the jack and it did not move. No twist.It may be just me, but any of the bolt-ins strike me as stabilizing the subframe to unibody connection mostly along the length of the car - fore/aft - rather than stiffening the subframe to unibody connection against twisting. I used DSE weld in SFCs, welded two long 1/4" by 1.5" (IIRC) "ears" on each side of the subframe, sleeved the SFCs so they wouldn't collapse when the bolts were tightened and used two 1/2" Grade 8 bolts on each side. It's pretty stiff but I can still pull the subframe should the need arise.