This is because of Mitsubishi's method of giving the Starion speed sensitive steering. The Starion employs a flow-sensitive valve inside the pump that reduces power steering pressure as flow increases, giving the effect of stiffer steering for high speed operation. Unfortunately, when you're spinning 6000 rpm in a slalom, it has the nasty effect of making your steering feel like it is locking up and properly screws up your times.
Unfortunately I didn't take any photos of what I did, but I found that googling for "mitsubishi power steering pump modification" came up with several results showing the same method. Here's one result:
Following that guide, I took the valve assembly out of the pump (it's the plug that your high pressure hose attaches to) and pressed it apart using a punch and socket as detailed in the dsmtuners post. I my case I shimmed the valve using a spacer I machined from aluminum (edit: but washers can be used as detailed in the DSMtuners post. I believe whatever is used must have a hole in the center for oil to flow through, but I can't recall for sure). If memory serves I shot for the middle of the road at 3mm.
The end result... no perceptible change at all with the exception that I had power steering whenever I wanted it! Driving on the street or highway had no change in steering effort or feel, but on the autocross course I've never encountered a power steering problem since.
Based on my experience, I'm actually reasonably sure that Mitsubishi's variable steering method is more for track racing where you can top out the engine at higher than freeway speeds. I haven't taken my car to a road course since the modification, but I'm reasonably sure that the steering will still be just as controllable as it was before the modification.
That said, I don't recommend doing this modification unless you've encountered the problem. It wasn't until I installed coil overs on my car that the chassis could react fast enough to require faster steering inputs.
Edited by Maxzillian, 30 October 2013 - 10:03 AM.