I kind of want to give you guys a graphical illustration of the problem with running rubber body bushings in first and second gen F-Bodies when power and traction is significantly increased over stock.
I'm currently in the process of replacing bushings and adding subframe connectors. Here's a look at the driver side mid-body mount
Looking at this you can see that the bushing itself while not in the greatest of condition, isn't completely mangled and deteriorated. These are wear parts and were never designed to last the age these vehicles are. I don't know if these bushings are what the car was delivered with, but I'm assuming they are.
What you will notice however is how the washer that holds the bushing together is folding like a taco. What is occurring here is that due to increased torque and levels of traction, the body of the car is trying to rip away from the subframe mount.
This is in part due to the car's unitized rear chassis. As the axle takes torque it wants to twist. That twist translates to the front eye bushings of the leaf spring and physically wants to pickup the body of the car. The subframe, with all the weight of the engine, transmission and front suspension is along for the ride.
Keep in mind, my combination isn't even crazy. At my altitude, my trap speed vs weight indicates about 330hp to the tires. While much larger than factory, my 245/45/17 and 275/40/17 summer performance tires aren't crazy either.
The ultimate solution is a full frame of course, like The Heidts frame or a Roadstershop SPEC or FastTrack. But 15-30K for a full frame isn't realistic for a lot of people, me included.
The next best option is to physically weld the subframe to the body and connect the two ends of the car with a set of subframe connectors. The DSE through floor connectors are a popular choice here. Until full frames became available, this is pretty much what you saw in every serious build. Not only does it provide a large increase in strength, it also has the benefit of lowering the front of the car without losing any bump travel. With small LS engines, there's typically no big issue, but with a big, tall Pontiac you can run into hood clearance issues doing this.
For cars that are complete or don't want to have the floors cut, the next best option is solid body mounts with an incorporated set of under the floor subframe connectors. This is the solution I'm working on currently.
Any time you say the word "solid" concerning the front end of these cars, you always get a lot of naysayers talking about noise, vibration and harshness. There are "some" trade-offs here, but mostly the people that complain about such haven't actually riden in, driven or own a car with solid bushings. Almost all modern cars have unitized chassis that are literally part of the body. This exercise is achieving that same thing.
What to look out for in the bushing department is the early aluminum offerings that were little more than round pucks. Because of their design they would spin and chatter against the body and the frame, not transmitting, but instead creating some of that noise. What you want is a set of bushings that interlock with each other and physically sandwich the frame between the interlocking junctions.
I opted for the RideTech subframe bushings because not only do they interlock, but the frame to body portion of the bushing is Delrin which provides 95% of the stiffness of aluminum, but also acts a diffuser for noise and vibration.
The last piece is tying the front subframe to the rear unitized frame. I again opted for the RideTech connectors because of one main reason. That being the integral front eye mount for the leaf springs or aftermarket 4 link systems. This ties them directly to the frame rail and bolsters an area of the chassis that takes much of the forward drive forces. The front of the connector is also captured by the rear body bushings, which lets these work better as a bolt in option instead of a weld-in option.
FWIW I do think that the Chassis Works g-connector system is probably the best option for a car that can't have a welded in subframe, or a full chassis under it. But that system is much more expensive and the installation requirements are much more in-depth.
One thing I wish the RideTech subframe connectors had, is a relocation of the front eye mounts. Raising the front leaf spring perch would really help anti-dive in these cars and would also likely help out with wheel hop as well.
This got a bit long, but I hope it illustrates the importance here of ditching the rubber (or poly) bushings on cars that are anything other than stock, or near stock. In my eyes the poly options should never even be considered. They do nothing but gain you the compromises of a solid body bushing with only a very small portion of the benefit.
Cheers!
