What are these feelings? (handling questions)
 

I just finished a track day at NJMP Thunderbolt and was experiencing some handling conditions that I'm not sure how to address (or even if it's abnormal) and would like your opinions. I noticed on turn in the rear of the car would feel like it lifts up and slides a bit and I'd have to correct with the steering. I tried a couple things like lowering tire pressure and playing with the rear suspension stiffness but it really didn't seem to help much.

The car is setup as follows:
- '91 with 1.8 LSD
- Xida 700/400 with stiffness set on 10 and 8
- 15x9 6UL with 225 R-S3
- stock sway bars
- Strut tower brace up front
- Frame rail reinforcement
- no rear bracing

It may also be driver error....

Are you still on the brakes when turning in? If so, I would expect exactly that behavior.

No, I'm not. I'm trying to just focus on getting my braking done before turn in. I'm starting to think the rear is too high compared to the front. I set it at a half inch difference at the pinch welds but they were pretty beat up.

not enough trailing throttle, giving minor compression locking?

Does sound like too much weight to the front / trail braking too late on entry. The stock sways may exacerbate it a bit too (949's recommendation for those spring rates with the usual RB/MSM combo has more relative front stiffness).

Try disconnecting one end link on the rear sway bar and tie it out of the way. If it corrects the problem, remove the sway bar

Turn-in/trail braking oversteer; too abrupt of a transition onto brakes while trying to initiate turn in, or too much weight transfer off rears. If tire pressures/temps aren't abnormal and you're rake isn't way out I'd try dropping the rear 1 turn on the perch.

What's your alignment like?

You've read this right? Miata Race alignment

Bingo.
I'd start by adjusting for less rake and driving it again.

yes, using the dual purpose alignment. I have a RB front bar waiting to be installed. I think I'll grab the 14mm rear from Goodwin and maybe drop the rear by a turn or two.

correct me if i'm wrong, but only putting a stiffer sway bar in the rear lowers rear grip and raises front grip. but lowering the ride height in the rear increases grip... so not really sure if it would act much different. bigger sway in the front and lower rear height would certainly increase rear grip.

Just complete the big grip kit (get recommended front and rear sways) that the alignment specs you are running the parts for actually work for, and youshould be fine.

What are your pinch weld heights?

That combination will be relatively soft in roll. Despite that roll, grip and compliance should be excellent. What you will gain with stiffer say bars is quicker transitional response and more precise response to throttle and steering inputs. We would recommend the 54104 and 14mm rear, our SBK for it.

It is 4.5 front and 4.75 rear estimated as the fronts are pretty beat up. Might be more like 4.25 front.

I should have your recommended setup though I'm not sure if my front bar is the same. Do you know if there's a PN stamped on the bar someplace?

Rake should be about level or 1/8" with driver. Your OP stated stock sway bars.
Our bars are marked with part numbers, 1-1/8" front and 9/16" rear.

I just wanted to try and identify the front RB bar I bought second hand. I'll take a look tonight.

Confirmed, I have the 1.125 hollow front bar.