Quote:
Originally Posted by Thegrim
I did read the entire thread. My specific concern is with the impact of harsh road bumps and the impact it will have on the car. I was also wondering about if there was any necessity to reinforcing the subframe itself with boxing for a DD/HPDE car.
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The torn/ruined subframes you see on old E36s and E46s is from the lack of rigidity inherent in the standard rubber subframe bushings and how they deteriorate over time. Even with new rubber bushings the subframe moves around and puts force on the subframe mounting bolts that are secured to the unibody. Over time this wiggling/movement ruins subframe mounting bolts and eventually will tear your unibody.
With solid subframe bushings, the subframe and the unibody are effectively one piece in which case the responsibility for soaking up shocks is placed on the suspension where it belongs and not on the subframe bushings or unibody. Further, the lack of ability of the subframe to move around increases the handling characteristics of the car.
I have a DD 165K mile E36 M3 that I plan on upgrading to solid subframe bushings. You will need to have your subframe mounting points inspected prior to installing any new bushings weather you plan to continue to use rubber, PU or solid. Turner makes some good weld in plates that might be a good idea regardless.