911 Carrera RallyCross Project

4 minute(s) of a 245 minute read

Big push over the next few weeks to get the car ready for the Porsche Parade at the end of June while simultaneously prepping it to tackle Autocross and track days as well as it's primary purpose; RallyCross. If there's one car that can shine at all three disciplines it's a 911.

By way of a warm up exercise we installed the repaired speedo/odometer and replaced the clock with a volt meter.




Then, onto the lowering project. When we replaced the broken rear torsion bar we set the car quite high as it had no underbody protection so was a little vulnerable. At 28" front and rear it was at least further away from the nasty stuff. Now, with skidplates etc installed and the looming track and autocross season it seems prudent to return it to something approaching stock ride height. For the US this seems to be 25.5 front and 25" rear as far as we can tell. This is measured from the floor to the top of the wheel arch.



This was measured with 195/65-15 rally tires at 32psi which happen to be the same diameter as the stock tires.


We didn't get chance to measure a baseline when we got the car as we broke the torsion almost immediately but we did measure the angle of the unaffected spring plate at 34.5* using a handy iPhone app. so we thought we'd aim for this. Reading the workshop manual also suggests the spring plate angle for this car (US spec) should be 35* so it should produce something similar to stock ride height.


The plates were both where we set them last time at 40.7* and 39.9*

 

With the torsion bars having 40 splines on the inside and 44 splines on the outside we figured you could tweak the angle in increments of 0.8* by turning one spline in and one spline out. On the left side we were looking for a 5.7* change in angle. If we divide that by 0.8 we get 7.125 which should mean if we turn the bar on the inner splines by 7 then the outer end by seven in the opposite direction it should result in about 35*. In effect, you can't turn the spring plate 7 splines as you have to take it off to turn the inner splines but, if you adjust the inner to 7 then in theory you should be able to put the spring plate back on in a position that would correspond to 7 splines of outer adjustment. Even though that's a bit long winded it actually worked, on both sides of the car, almost perfectly. The only problem being that when we bolted it all back together we only got to 26.75" of ride height! This is with the dampers still unbolted and the suspension bounced a few times so it should be accurate right? Maybe the car has lost more rear weight recently than we appreciate. I think we will be dialing out some more height later today.


At least while we were in there we did get to replace our missing torsion bar end cap cover with one from a Pelican. Thanks Bob.




Possibly the most significant modification we plan isn't to the car but to the driver. Cheap too.