Hey everyone, I've designed my own coilover kit using the Bilstein AS2 line of parts as its basis.

Here's a image of the front and rear designs in CAD:



Here are some shots of the machined parts before installation:



Here's a picture of the shock dyno and assembly:



Installed in the car:



Images of the shock dyno graphs:




I went with 700 lb/in front and 375 lb/in rear spring rates (12.5 kg/mm front, 6.7 kg/mm rear). The rear is installed as true rear. I calculated an approximate damper curve for those spring rates and matched the real life builds to those theoretical curves. The Bilstein AS2 shaft I used has an "open" adjuster, so it adjusts both compression and rebound simultaneously (single open hole).

So far I've put about 1k miles on the parts and I'm quite happy so far. The ride is very firm, but not harsh at all, and the handling is definitely sharper with those spring rates. My plan is to turn this car primarily into a track day/weekend mountain car, and this coilover kit is a good step in that direction.

I'm reaching out to the 350z community to see if anyone would be interested in a kit like this... I can order these parts and custom build a kit for anyone. Also, Bilstein shock parts fit inside BC Racing shock bodies, so I can also build these damper curves into an existing BC Racing unit if anyone wants a retrofitted kit.

Feel free to reach out with questions and comments. Thanks for reading!

 

nice job. let us know how they hold up after some track days

 

Do you have any length documentation? As in compressed length to bumpstop vs oem and total droop vs oem? It appears that there is not damper height adjustment, only spring seat adjustment which is fine, but I am curious on where the damper sits in operation and the total sweep lengths vs an oem damper setup.

 

Great question. My basic design was to have the free length of the assembly be 0.5'' shorter than the OEM for both front and rear. My OEM benchmark was the NISMO S Tune kit since that's what I had on the car.

The measured front stroke is 3.93''
The measured rear stroke is 5.5''

The Bilstein shafts can be purchased in various lengths, but my goal is to use a shaft that is, at minimum, capable of the same travel as OEM. Therefore the shafts I designed around are:
5'' front shaft which allows for 4.71'' of stroke
7'' rear shaft with allows for 6.58'' of stroke

The Bilstein threaded bodies can be purchased in various lengths, the practical limit being the shaft length. You must choose a threaded body that can accommodate the chosen shaft stroke.

With those choices made, I designed the mounting to create an assembly that is 0.5'' shorter than OEM. This sounds simple, but I screwed it up and had to remake the lower mount on the front coilover. The rear assembly ended up slightly longer than I expected, but close enough to not have to make new parts. I have V2 designs for all that stuff.

The bump rubbers are really there just to protect the internals of the shock. I don't expect any bump rubber engagement since the spring rates are so much higher than stock. That said, as I test drive these units I'll pay attention to shaft travel and bump rubber engagement. Engagement gaps can be tuned with packers.

The ride height and travel theory I've subscribed to is the 1/3 rd theory. You take the total travel of the shock and multiply by 0.3333. That's the amount of rebound travel you want from curb ride height condition. The other 2/3rds of the shock travel is used for bump. Adhering to that rule works pretty well in my experience. The spring length and preload are chosen in concert to have 2/3rd travel available for bump and 1/3rd available for droop.

If someone wanted this kit to be super short or something, then you can choose the shaft and body length to target a specific ride height. For example, rather than being 0.5'' lower than stock, you might want to be 1'' or 1.5'' lower than stock. That can be achieved by using the appropriate length shock body and shaft.