Thanks Ed.

Lol, yes, I am looking to spend like a tenth of that. But it does make beautiful pieces.

Any idea how much weight you lost with the swap? Or specifically how much lighter your aluminum adapter plate is than the Kmiata steel piece?

The weight was 2630 with me before the swap, and 2480 after. It lost 150lbs which is good, but F/R bias didn't change. I was hoping it would. The more I think about it, the car lost about 30lbs from mostly the rear, which explains the lack of F/R bias change. The K swap itself resulted in about a 120lb loss.

The aluminum adapter plate was 6lbs lighter. I wouldn't worry about using the steel one.

This is an awesome build!
Could you lend some more info about your shock build? It's not everyday we get the opportunity to chat with a suspension engineer.

I want to preface this with restating your note that there are numerous awesome low cost options for the miata.
However the AS2 is much more general purpose and could lend to helping both miata and non-miata projects.

Namely when I look up the AS2 with my highly functioning caveman skills, I can't find much other than non-adjustable circle track stuff.
Where would one buy the drilled/jetted/etc shaft and the bleed screw adjuster?

I believe you can specify these to Bilstein when ordering parts for the AS2

https://cart.bilsteinus.com/Portals/...-2019(WEB).pdf

I'll post some info on the shocks. It's hard to think of what to say, you could damn near write a book about it. I'll show the basics and if people have questions they can ask.

Harry is right about the shaft, you can spec that on the order.

Bilstein AS2 Info
 

Here's some notes on the coilovers:

First, as said before, this is not the best solution for most people. You need to know how to purchase from Bilstein (not easy), understand oil flow (through different piston types and shim stacks), and have a direction to go (force/velocity data), and have a method to validate (shock dyno & on-car data acquisition). If you don't have all four of these, you probably don't want to go this route unless you are a glutton for punishment which I think we all are.

1. Purchasing: Honestly I don't know how most people would even get through this part. My work is a dealer of Bilstein, so I just send an email and the part shows up 5 days later. I don't even get a confirmation email, it just shows up - what I'm getting as is Bilstein is a huge ass company and they don't have much time to chit chat with us car guys. Sure, you're speaking to the motorsports division so they're car guys too - but their customers spend thousands or ten times that. This means most of the time you have to deal with a Bilstein dealer which really slows things down if you don't have part numbers. Get the part numbers you need, double and triple check, then call a dealer. Each shock is $595 IIRC.

Ok, so you purchased the shock. But wait, there's a huge problem! There's nothing inside! It's a dry shock. Yes, you just paid $595 for an empty aluminum coilover. What you bought was the lower body cap, threaded body, upper cap, digressive or linear piston (you know which one you want, right?), adjustable shaft, and the adjuster. They way I understand it, and it does make sense, if you have the balls to get this far and purchase this thing, you know what you want for a shim stack. You already have shim assortments, tools, oil, nitrogen, etc. You don't want Bilstein to tell you what to run because it's your car and you know it best. Ugh.

2. Valves and shim stacks: Obviously I can't explain everything, but hopefully I give some tips to maybe make this possible to some people who are as retarded as I am. You have three piston choices, and these determine what valve profile you will have. Your choices are linear, digressive, and COB (check on bleed). Here's the thing: you can make a linear piston behave like a digressive by the shims and vise versa, but COB will be easiest to get high low velocity force (little low speed bleed) which is what most of us want. Problem is, they are tricky. Linear is easy, COB just adds a level of complexity that makes oil flow a bit more difficult to control. But when you got it, it's good! Now, on to shims. Shims are easy, they just flex and allow oil to flow past them. Shims vary is thickness and diameter to allow more or less flex and WHEN that flex happens (either high or low velocity). Shims closer to the piston control low speed bleed, farther away controls high speed bleed. Now, for DA shocks, keep in mind the shaft is 12mm in diameter unlike the non-adjustable which is 8mm. You need to buy shims with a 12mm ID hole for double adjustable shocks. This seems obvious, but for some reason they're shim assortment kit only comes with 8mm ID shims. You need to build your own kit, and it's going to cost a few hundred $$ (unless if you already know the shims you want, then just buy those shims).

3. Goals: You need to know what you want before you get started. I have an excel spreadsheet that kicks out force/velocity data based on inputs I give it. Garbage in, garbage out. And, you have to tailor the numbers based on "intuition". That's the trouble with engineering suspensions, there is no right or wrong answer. It's more of an art. And I hate art. I like math, 2+2 always equals 4 no matter what. But I think that's why suspension engineering is a black art, it's difficult to take all this data, then put your own personal touch on it. But over the years I've gained enough experience to be confident in getting a good result the first time. So, what I'm saying is, you'll need to do the math on roll centers, g loads, critical damping blah blah then use coefficients to modify the output slightly to reflect how you want the car to behave.

4. Validate: I couldn't do this without a shock dyno. If you have access to one, good for you and I'd give this a shot. On-car data acquisition will get you to the end result faster but isn't necessary for non pro-level guys. Count on doing probably 30 dyno sessions trying to get the valve dialed in if you know what you are doing, 3 to 4 times that if you're a noob.

I guess it's it for the basics. I'll post some pictures for illustration. If you're new to this, I would just copy somebody else's valve (look online or use one of the examples in the Bilstein rebuild catalog). You are NOT going to get a valve as good as Xida's quickly. It's going to take you lots of time and a dyno for sure. If you want to learn shocks inside and out, rebuildable Bilsteins are awesome.

Coilover photos
 

https://cimg5.ibsrv.net/gimg/www.mia...b63f2a53df.jpg
This is what you purchase for $600. This one has the bearing at the adjuster, Miata's will use a stem type mount shown in the Bilstein catalog. You need to specify you want the stem type shaft when you order the shock!



https://cimg3.ibsrv.net/gimg/www.mia...4f85a65fbe.jpg
Close up on the adjuster. Very high quality, easy to read, strong detent with a satisfying "click". Notice the red and blue adjusters are actually two piece so they can be indexed if needed.



https://cimg6.ibsrv.net/gimg/www.mia...44ef9013db.jpg
Another cool thing about Bilsteins: If you don't see the length you need, get the longest one and cut the threaded body down. You'll want to do this on a lathe to ensure you have a good o-ring sealing surface. You can remove the lower body cap by heating it as there is lots of red Locktite.



https://cimg5.ibsrv.net/gimg/www.mia...82f4ce63bf.jpg
Here's a linear (left) and digressive (right) piston. Noobs may opt for the linear as it's simple.



https://cimg7.ibsrv.net/gimg/www.mia...126fb1abf3.jpg
Here's the shim layout and DA shaft. Lower row is the compression shims, upper is rebound. The bleed shims up top (the ones with the notches) shouldn't be there, I didn't clean up after myself. Be METICULOUS with your procedure, it's so easy to get shims mixed up. Come up with an assembly procedure and do it exactly the same each time.



https://cimg2.ibsrv.net/gimg/www.mia...add9dce840.jpg
Shims for 12mm shaft



https://cimg5.ibsrv.net/gimg/www.mia...7e2ae98e4d.jpg
More shims

Pos-cats for super informative posts; especially the 1st one should be directly pasted to my ex-FSAE team suspension discussion.

Thank you. I still owe you a pm.

I just realized how many spelling errors I had, Damn. Embarrassing.