When I swapped from OEM to the centerforce DF clutch, I started having all kinds of clutch problems. There was nothing wrong with my OEM from an operations view, but at the time I was launching the car with spray and I could feel the clutch slipping a bunch. It also showed on 60' times. I thought the centerforce was the answer, but after having problems I searched deeper on centerforce clutches in S197s and it seemed almost everyone running one had similar issues. The general consensus was the pressure plate was simply too stiff or heavy for the slave to push. My issues were grinding gears, being locked out of a gear at high rpm, and difficulty getting into 1st/reverse from a stand still. At idle, with the clutch full in, the car would roll forward in 1st on a flat surface. It did the same idling in reverse. I finally read a thread on SVTP where a GT500 owner called Centerforce and asked about the same issues, the tech told him they would send him some shims and he would have to measure it out based on his application (slave/flywheel/transmission model). I called Centerforce and asked if they could send me the same shims, and the tech told me I didn't need shims for my application, and that I must have made an error on installation.
In the end I ordered a Exedy Mach 400 clutch, '13 GT500 master cylinder, OEM slave (came with the Exedy), SS braided clutch line, and a fadanza aluminum flywheel from a '02 GT (used, but replaced the insert). I haven't had a single clutch problem since, and been running this setup for 5 years now (through spray and now supercharged). Never had it slip that I noticed, never been locked out of a gear, never had it grind. The GT500 master cylinder may or may not be too much throw, and may or may not be damaging the pressure plate, but if it is, it's sure taking it's sweet time destroying it. My engagement point went from being at the very bottom of the pedal (or partially engaged all the time) with the centerforce, to being much closer to the top of the pedal, which I like preferably. I can move between gears at 2/3's pedal, which means I don't "have" to take it to the floor for the next gear, but I usually still do during spirited driving. The pedal is nowhere near as stiff as it was with the Centerforce. Obviously I didn't shim this slave cylinder either, if anything it would need to be shaved. But I like it just the way it is. Full engagement happens maybe an inch or so before full release of the pedal. IMO it's perfect.
Take from it what you will, but my advice, ditch the centerforce and order anything else. The exedy 400 is great for stock to at least 500ft/lb rwtq. And the '13 GT500 Mastery Cylinder is another great upgrade for a S197, IMO. It will make sure the clutch fully disengages.
As for the GT500 MC, most of my comments are hear-say and general opinion regarding a previous thread on using the GT500 MC. Some say the GT500 MC over-throws the pressure plate, there-by over-extending the slave and damaging both components. I've had neither one fail since they were installed, at least 5 years and 30-40k/mi. I can't disprove it either, as I nor anyone else has bothered to inspect or take measurements. I can only tell you what the clutch pedal does and how the clutch feels, and pedal distances for engagement/disengagement. I know that it performs perfect, IMO. And cured all my clutch problems since the centerforce. If the slave is riding on the pressure plate, those are some damn good bearings because they've taken a shit-ton of abuse and continue to, over the last 5 years. And I don't hear any clutch rattle or bearings.
