Wednesday, January 13, 2016

Shocks!

Here's an overview of the work I did to adapt a set of Ohlins TTX36 shocks to my car.  Why didn't I just buy a set of Penskes or MCS's?  It definitely would have been faster and easier but Ohlins USA is located about 20 minutes from my house and I know some guys that work there so I was able to get a little discount on my parts which made the cost less of an issue, and rebuilds/revalves are a manner of stopping by on my lunch break.  Plus the TTX dampers are the only 2-way shocks that have both low speed compression and rebound adjustments, which is the important region for autocross use.  And lastly, because they look cool and are unique!
 
Started with some stock shocks, a couple drawings of the interface joints on the TTX's, and some Delrin spherical upper mounts based on a Hardbar/Banski design.  The fronts were easiest since they use a T-bar lower mount and a pintop upper.  Only thing I had to figure out was how to go from the Ohlins shaft threads to a C5 upper mount, and what size T-bar I needed to make.

Some CAD time and a little lathe work by a local machine shop, and we have a front shock.  Uses an Ohlins spherical bearing with a machined T-bar for the lower mount and a custom adapter from the Ohlins shaft to the spherical Delrin upper shock mount.


Here is one of the shocks getting dynoed at Ohlins USA.  I spec'd out the valving based on stock C6 Z06 high speed with a fattened up low speed zone.  One of the benefits of the TTX shock is that it has massive adjustment range so that even if I guessed off on the valving (which I was pretty far off on the rear shocks), you can still turn the clickers and get them dialed in.

Here is the first iteration of the rear shocks.  Same upper mounts as the fronts, with new pieces to go from the TTX bolt pattern to the C5 lower control arm. 

Ended up needing a spacer to clear the reservoir.


Spacer welded in.  Not the prettiest mount but it works as a prototype.  I am planning to update these to a single machined piece.

Finished rear shock.  Laser cut upper mount also pictured, which replaces the stamped steel stock upper mount.  I made a flat piece to take some stack height out of the assembly to get more shock travel.  Rear upper mounts are being updated for 2016.
 
So how do they drive?  Fantastic!  Going from C6 Z06 shocks to these was an incredible difference, both in general body control and in the fact that I was able to quite easily adjust them to tame some bad habits the car had like excessive corner entry oversteer.  I used Neil Robert's shock tuning guide and in the course of a single 2-day autocross event was able to make big changes to how the car drove.  I am now able to attack transitions and corner entries much harder than before without fear of the car losing control.  

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