Quote:
Originally Posted by The Radium King
the oem plate was specifically designed to direct airflow over the transmission, no? also, the oem plate ties back to the brace (the one used as the subi engine mount). is not the oem a bit better as a result?
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actually, the OEM shear plate is designed as a stress member. a side effect may be airflow directed at the transmission.
the part shown in the subi conversion improves upon this. a shear plate is a good choice in tensile applications. in this case, though, cornering forces will apply both tensile and compressive forces to the shear plate. a shear plate does nothing to fix subframe component locations when resultant forces attempt to move subframe components closer together (i.e. toward the center of the car).
the result is flex under cornering loads. this causes two primary concerns:
the first is at the lower control arms. without another structural component, cornering forces would push the lower control arm subframe mounts to move toward the car's center. this would result in loss of camber, particularly over bumps. porsche combats this with a boxed steel crossmember that bolts to the subframes, fixing their outward locations. kzpaz's component further improves upon this by placing the lower control arms BETWEEN two structural members.
the second concern is at the toe arms. in this case, porsche provided NO structure to support compression loads at these subframe components. the result is toe change in corners, especially over bumps. this can result in severe instability and snap oversteer. aftermarket 'lower stress bars' were designed to jack these points & keep them fixed under load. kcpaz's solution addresses this.
ultimately, porsche's shear plate would have been better designed as a trussed component, as kcpaz has developed here. it fixes these suspension subframe components for tensile and compressive forces in both longitudinal and lateral directions. the result will be a truly fixed set of locating points for all control arms & the inherent stability that comes with it. porsche's shear plate is a nice, cushy, CHEAP solution that works fine for a road car. on r-comps at speed, it doesn't measure up.