Thanks so much for your feedback Mike.
Let's take these topics one at a time
Shocks/Struts and Springs
1) Over-dampening won't hurt handling, as long as it is evenly over-damped. It will hurt ride quality, but I don't think you are concerned about that. Honestly, SC springs with 1.5 coils cut off are plenty stiff for the chassis. Going too stiff can actually hurt handling because the chassis will flex rather than the suspension, which behaves unpredictably, and if the chassis is stiffened up enough with the cage, the car will start lifting the inside rear wheel in a turn, which means that tire won't have any traction.
1b) Bilsteins aren't made for the front of our cars. The stiffest aftermarket shock you will be able to get is the Tokico's. The Tokico Blues are pretty good, and will be way better than what you have, but if it is in the budget, the Tokico Illumina 2's are meant for the SC with the ARC setup, and if you set them to the firm setting and lock them there, that will be the stiffest bolt-in shock you can get for the front of this car. For the rear though, definitely go with the 03 Cobra Bilsteins.
2) As I said above, I think your front springs are plenty stiff. I suspect your Monroe Sensatracs are beyond shot after running even one race with those springs, let alone several. Keep in mind that when you cut a spring, you increase the stiffness of the spring by the ratio of coils you have now to coils you did have. In other words if a spring has a 400lb/in rating, and 10 coils, and you cut one coil off, that spring now has 444lb/in rate. If you cut 2 coils off that same spring, it is now 500lb/in. This gets a little more complicated for progressive springs, but the concept is the same, so regardless, right now up front you are horribly over-sprung. As for the rear, I think the Eibachs in the back are a weak link for you, and I would look to change them. There are varying degrees of progressiveness of a spring, and the eibachs are very progressive, meaning that they start very soft, and then get very stiff. This is great on a street car because you don't really sacrifice ride quality, but on a race-car, it makes the car less predictable. If possible, I would look for a set of SC springs to match the fronts, and then cut a coil off those. If those are not available, swapping to the suspension techniques springs all the way around should be an improvement.
As far as the shocks/springs go, I know Bilsteins are no longer available as a direct fit item but Paul and some others did come up with alternatives which insert available circle track shocks into the stock strut body.
Bilstein 36mm inserts S7G-5555 aka F4-BE3-C239-H0 (pauls says too tall for lowered car)
Bilstein 36mm inserts S6G-5555 aka F4-BE3-A213-M6
Seeing as I have a blown out strut already available and some time, I prepped it for dropping in a Bilstein insert and I could easily do another one (esp since my driver's side strut is probably also worn out. At $75/ea, this seems a reasonable price for the Bilstein inserts. I know other people have used Koni Race inserts but at $350/pair, they are a bit more than I want to spend (I don't want to get bumped up to A class in the west coast races).
Koni 86111259RACE Road Racing/Autocross Double Adjustable Twin Tube Strut Insert | Autoplicity
Q: How well do you think these Bilsteins would last on the track, Mike? They have the added benefit of being DIY/shitty looking compared to the Tokicos.
In comparison, the Tokico Illumina EU3689 struts seem to run ~$150/ea which seem to be crankable to max stiffness with a Tokico adjuster tool (#TO00102) -- or a screwdriver.
Bottom Line: I really wish I knew someone near me with a shock dyno to tell me how crappy the shocks I have around are.
If I do upgrade the fronts, I'll go will bilsteins for the rear and grime them up.
It doesn't sound like keeping the existing spring setup would be detrimental if I replaced all four struts/springs with stiffer ones.
Q: How bad an idea would it be to replace the rears with Bilsteins shocks and leave the soft Monroe struts up front?
As far as the springs are concerned, I'm surprised that you would recommend going with softer SC springs in the rear. Even if the spring rate goes up with a coil being lopped off as you suggest, I'm skeptical that the SC would be any better
SC springs: 509-637 lb./in.
Eibach: 514-714 lb/in
None of my drivers have complained about unpredictability in handling with the progressive springs on the front/rear; it doesn't sound like you'd approve of going linear on the front and progressive in the rear though.
For giggles, we may just run with the ST suspension to see how linear springs on all four corners feels like.
. Curiously enough, they came off a donor 5.0 car owned by a grandpa who drove the car into a tree (broke the header panel that holds the headlights) and they pulled his license.
As for other suggestions, I know you said you are not inclined to change the sway-bar, but running the stock 95 V6 bar, you are basically running the smallest factory bar ever made for these cars. Even stock SC sway bars front and rear would be a huge improvement in this area, as it would keep the car much flatter in the corners, but you have to match the stiffness of the front and rear sway bars. If you go too stiff in the rear without changing the front, it will induce oversteer. If you go the other way, it will induce understeer. I know it sucks having to pull the subframe down to replace the front bar, but I think it will help. If you are dead-set against changing the sway bars, then stiffening up the spring rate can also counter the lack of stiffness in the sway bar, but once again, it will have to be matched front and rear, or you will induce oversteer or understeer depending on whether the front or the rear is stiffer relative to the weight on that wheel.
I did upgrade my swaybars -- the rear is from a 90SC which did seem to help a good deal since it's solid vs tubular. IMO, that helped the car really be neutral in the turns when we had a V6 up front. Now, I feel I have to goose the throttle more to get the car to turn in more quickly on sharp turns and going to a larger front swaybar (from 1.06" solid like I have now to the 1.1" solid bar I have onhand from a 93SC) is only going to induce more understeer.
Another thing that is simple and cheap and will be a huge help with handing is front suspension bracing. A brace across the bottom of the front subframe from near where the LCA mounts to near where the front strut rod bushing mounts, and another brace from the bottom back of the rear subframe to the bottom of the frame rail will do wonders for your handling, and all is costs is some 1" square tubing from Home Depot, and some time with a MIG welder.
Q: Do you have any pics of what those subframe braces might look like?
I took a look at my bushings and yeah, both the front and rear swaybar bushings are rotted out and need to be replaced. I'm skeptical about spending the time/effort to replace my rear LCAs inner bushings.
One easy one to replace would be the diff bushings as they look old but not necessary flattened out/rotted out.
At the same time, I would consider running a bolt through the rear diff brace and reinforcing the diff face so the bracket doesn't crack off the diff cover.
As seen in the last section of this first post
Q: Any thoughts on the value of stiffening the diff mount on the car?
Also, I know it will hurt the budget, but if you want to be competitive, you need to step it up on the tires. This is a heavy car, and to keep up with those lightweight little Miatas and E30s in the corners, you need a lot of tire. A Mustang hub swap will open your door to tons of cheap 17" wheels.
Yeah, I thought about doing a hub swap and getting two sets of 17" wheels but I just stepped up to 16" rims so I'm not terribly keen on abandoning them just yet. We have two sets of 16" rims in good condition with Direzza SS tires.
I don't anticipate quitting lemons racing anytime in the near future (having a kid hasn't changed my enjoyment of the project -- just the amount of time I can devote to it) so I will probably do a hub/wheel upgrade in conjunction with a 13" Cobra PBR swap upgrade once I decide that I need more braking.