Making a car fast on any course is a combination of many things...first and foremost, the car needs to be neutral balanced so the driver isn't fighting one end of the car or the other loosing traction first. Once the car is neutral balanced, it is up to the driver to get the most speed out of the car in any given corner. Different driver inputs can affect the way the car handles (usually referred to as the driver mod) both positively and negatively. Then one might also have other mechanical issues the driver and car must work around that aren't really chassis related that affect speed. How a driver\tuner deals with all of the above is typically fluid and it is only once all of the above are almost perfect that one will run at or near the top of the speed charts in any given competition.
Throughout the multiple stages of development on this car (with Ron's fantastic help) we've done a pretty good job at keeping the car neutral. We reached a plateau last fall after the addition of the much stiffer front bar and the car had a loose condition mid roll through to corner exit that we could not tune out. Enter Stage 4 I call it, a huge jump in rear spring rate.
I ran one event last week with the new springs and had some tuning challenges. I could tell the springs fixed the issue we intended on fixing, but a few other issues popped up that we had to contend with and with only 4 runs at a typical SCCA event I didn't have enough time to dial everything in.
After some discussion with Ron, we came up with a few more tuning ideas and I entered another SCCA event in Topeka last Sunday with the intention of using multiple runs on a much faster freer flowing course to dial things in further. I can say now that the car is neutral once again and has MUCH more rear grip on mid roll through to corner exit. It took me about 4 runs to get the rear shocks and tire pressures set where I needed them and then I used the next 4 runs to work on the driver mod getting him used to the new setup.
Another issue reared it's ugly head once again though, I've wore out yet another clutch type posi unit and spent just about every right hand corner exit spinning the right rear tire while trying to put the power down which I'm certain really hurt my times. If you can't put the power down, you aren't going to go fast. Watch the right rear tire in the first run, you'll see the black marks it leaves on most corner exits. The second run in the video was my last one during the fun runs after the event was over and was my fastest run of the day (in the 96 degree afternoon heat even). I finally started to get a good feel for how the car was going to react and dealt with the posi issue the best that I could.
It'll take some more work (and $$$) to fix it even better but that's why we do this...right?
I'm trying to decide now which direction to go with a diff replacement. I know a certain green car that has dealt with similar diff issues and just installed a locker...I can't wait to hear how it does on course with this new addition. Some autocross gurus recommend against a locker, while others like them. I have no idea which way I'll most likely go...all I know is it will NOT be another trac-loc going back in the car.