Wow, there's some whacky advice and "facts" being given out in this thread so far! I think some people here aren't quite sure how suspension dynamics actually work. Let's hit "reset" and start over with answering your question.
Truly, oversteer is not what you're looking for because it's really slow. However, most people really don't mean they want the rear end to actually lose grip first in a turn, and I suspect you don't either. If you need to cancel out understeer in your car (i.e. get closer to neutral), a stiffer rear swaybar will accomplish that. But you don't want to go too far or the car will get slow and difficult to drive near the limit - not good. The others aren't wrong when they say that too much rear roll stiffness (be it from swaybar or springs) kills your ability to put down power). You definitely should not try a softer front bar! That's ridiculous for several reasons, but mainly you need to limit your car's roll* during cornering as much as possible, so a softer front bar is the wrong way to go.
But here are some suggestions for increasing your rear roll stiffness, including the adjustable bars you actually asked about (be patient and we'll get there!):
- Believe it or not, just changing the rear "D" bushings that mount the bar to the frame to harder urethane will stiffen the stock bar's effective rate. That's a super cheap and easy thing to try.
- I think the next stiffest (compared to stock) rear bar you could get would be the SS 1LE (FE4) bar. If you can get that part cheap, you could start there. It's not adjustable, I know, but it is stiffer than your stock rear bar. And with rear bar rate increases, sometimes a little goes a long way. The next stiffest is the BMR non-adjustable rear bar, which is supposed to be 16% stiffer than the 1LE bar. But I'd probably skip that in favor of what's next:
- The softest adjustable rear bar I know of is the Hotchkiss. At its softest setting it is 25% stiffer than the 1LE bar. The medium setting is 35% more and the stiffest setting is 50% more. Keep in mind that even at its softest setting, it will be quite a bit stiffer than your stock rear bar: start with the softest setting for sure. But this is why I'd start with the 1LE rear bar and see how that works. Finally, the BMR rear adjustable bar has rates that are 46/70/98% stiffer than the 1LE rear bar, which means anywhere from ~66%-230% stiffer than your stock bar. IMO, that's way too big a jump since you can't change the front to go along with it.
The very first thing you should do is make sure you've maxed out front and rear camber and that you're running zero toe at both ends. It sounds like you've thought of that already though. Also, I'm hoping you have a bought a set of 19" wheels and Falken RT660 tires in 245/35/19 front and 265/35/19 rear (possibly the 275/30/19 is worth trying on the back in this situation). Those are easily the fastest tires legal for Street classes that won't be destroyed on your car in a few runs. Don't waste a bunch of money on the lightest, fanciest forged wheels: a $1400 set of MRRs, Apexes, or Forgestars will do just fine.
Finally...I hadn't even considered that good performance struts and shocks may not exist for a Street class Camaro! Unless you have Magride on your SS, that's...a really serious problem. Other than tires, shocks are probably the biggest improvement you can make. And if you experiment with bigger rear swaybars, adjustable shocks will be really important to help keep the car stable in offsets and slaloms (more front damping stiffness). For that matter, you could keep your current rear bar and just try stiffer rear damping rates to dial out understeer on corner entry. In the rear, I don't know why you couldn't run the shocks from a coilover kit and just omit the spring and perch while retaining the stock spring. That's legal. For the front, I don't know of a strut that allows the use of the stock spring and perch. But I know one thing: I'd get on the phone with Vorshlag and Strano and I would beg, borrow, or steal a way to get good adjustable damping on both ends of the car if I were you! If there's no way to run anything better than your stock dampers, you're ****ed. Pure and simple. There
has to be an option or two out there. Find out what nationally competitive FS Camaro guys are/were running for dampers.
Which brings us to the bad news. I don't know any other way to break this to you other than to be brutally honest: the non-1LE SS Camaro is hopelessly outgunned in F Street. Currently, the E90 M3 is way faster and nobody good will compete in anything else at the national level. That's why the class is dying. Same goes for the Mustang GT, btw. And next year, things may get worse because SCCA may move the 1LE and GT350/PP2/Mach1 into F Street to save the class. No matter what you do to the car within class rules, you're always going to be at a major disadvantage to several other cars in class. If I were in your shoes, I'd bail on F Street and move to CAM-C, where you could run way wider wheels/tires, aftermarket coilovers with any spring rates you want and any swaybars you want, along with camber plates and (maybe) an aftermarket diff. A local friend has done just that with his 2017 (minus the coilovers - he has the Magride shocks) and I co-drove it with him for one local event. I believe it is a bit faster than my B Street 1LE. I know this isn't what you asked about, but it's important to ask oneself whether it makes sense to throw money and time at a non-1LE SS for F Street at this point. Maybe you've thought this all through and have your reasons, which is of course fine. I'd just be remiss if I didn't make sure you have this perspective.
*Roll doesn't cause weight transfer, and weight transfer is bad for grip anyway; so please try to forget the stuff written above about roll being good!