Boxster Subaru conversion interest?

[kcpaz]

Originally Posted by insite

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.

Couldn't have said it better myself. You just saved me a bunch of time

As far as transaxle cooling, because I'm running an external oil cooler and spray-bar set-up above the gear stack, I'm not at all worried about transaxle cooling.

[Gilles]

Originally Posted by kcpaz

Couldn't have said it better myself. You just saved me a bunch of time

As far as transaxle cooling, because I'm running an external oil cooler and spray-bar set-up above the gear stack, I'm not at all worried about transaxle cooling.

kcpaz -wrote:

i like that truss you've used to replace the shear plate at the rear subframe. will you be selling these?

[/QUOTE]

kcpaz, + 1 your bar...!

I believe that your truss bar will be a nice compliment to the Mantis Sport rear stress bar that I installed a couple of years back

.

[kcpaz]

Originally Posted by Gilles

kcpaz -wrote:

i like that truss you've used to replace the shear plate at the rear subframe. will you be selling these?

kcpaz, + 1 your bar...!

I believe that your truss bar will be a nice compliment to the Mantis Sport rear stress bar that I installed a couple of years back

.[/QUOTE]

I could probably be persuaded to build some more. I just never pursued it because most of the Boxsters that are being raced are Spec cars and it's not legal in that application.

[The Radium King]

sorry if i was misunderstood. i understand the structural role the oem plate plays. i just noted that it also has air scoops build into it to direct air over the transmission, and that the boxster transmission needs all the cooling it can get. so , his system may work for a built transmission, but for the rest of us track rats we may miss the additional cooling. also, if you look, his truss system doesn't hit all the tie-in points that the oem plate does, so there may actually be some lost rigidity in some directions.

[kcpaz]

The only part it misses is the two bolts that go into the factory steel crossmember in the front and that part doesn't exist anymore. Instead, I integrated the engine cradle into those parts of the sub-frame so it's actually stronger than it ever was. Now the question is how strong are the 4 sub-frame bolts and their attachment points in chassis? I am planning on keeping a close watch on these and if I see any sort of deflection or cracking, I will be integrating the roll cage into those points.

[insite]

Originally Posted by The Radium King

sorry if i was misunderstood. i understand the structural role the oem plate plays. i just noted that it also has air scoops build into it to direct air over the transmission, and that the boxster transmission needs all the cooling it can get. so , his system may work for a built transmission, but for the rest of us track rats we may miss the additional cooling. also, if you look, his truss system doesn't hit all the tie-in points that the oem plate does, so there may actually be some lost rigidity in some directions.

hard to say whether the old plate increases airflow or whether there is more airflow with the transaxle completely exposed.

as to the tie-ins? i missed it before, but it looks like the boxed steel crossmember that connects the lower control arm sub-frame mounts has been removed in this application in order to make room for the exhaust and engine carrier. in its place are two provisions: the first is the lateral bar that ties the lower control arm subframes together. the second is the engine carrier itself.

in a boxster engined configuration, this truss could tie in with the boxed crossmember, as the OEM shear plate does, although i'm not sure if anything is lost by simply removing the shear plate & installing the truss as pictured on the subie car.....

regardless, i am awestruck by the amount of work that's gone into this. simply amazing.