Parts
I got some JDM Legacy B4 Bilsteins:
These are slightly shorter than the Outback struts but I'm considering getting the travel back by removing the separator pistons and adding remote reservoirs. Not that I will need much travel for the spring rates I want to run...
The fronts are inverted (win!!), with the piston attached to the suspension and the body of the strut on the car. This reduces unsprung weight and adds considerable strength to resist bending loads. It's basically a 36mm strut body flipped upside down with the strut shaft bolted to the end of the normal strut housing. Additionally, there are some teflon guides/seals so the inverted body can slide in and out of the housing.
I suspect I could convert these to take-aparts and revalve them myself with 36mm and 46mm Bilstein valving parts. However, I'm probably just going to have Bilstein revalve them for me once I figure out what spring rates I want to run. My target ride frequencies are 2.2 Hz (front) and 2.4 Hz (rear).
The rears have a 46mm body, so when I finish my
Bilstein Fiero suspension project I should already have the parts to revalve those as well.
Plan
I plan on using these struts to build a track-only suspension for my Outback. I will switch between stock for rallycross and the Bilsteins + stiff springs for track days. The rears change out in about 20 minutes, but the fronts are a bit more involved.. so I picked up a full set of front corners (strut, spring, tophat, knuckle, hub, rotor, balljoint, brake caliper) which I will swap in as one piece. I'll probably just keep the same calipers on the car, so that I don't have to bleed the system each time. Brake pads are open in stock class rallycross, so I can just run track pads all the time. Since the knuckle and strut won't change, the camber and caster alignment should be reproducible. I'll only have to realign the toe.
The only consumable during the switch is the axle nuts up front. I keep a stock of OE parts right now but I'll have to order a few more to make sure I always have enough on hand. Otherwise I guess I could just pick up another front axle (I already have one extra). It's just a split pin holding them into the trans, and due to the stub arrangement no oil comes out when they're pulled. Then I would leave the axle attached to the hub for each suspension setup.
Since the Outback is factory-equipped with ~25mm spacers on all the suspension points (it's effectively a body-lifted Legacy), I won't be able to lower it as far as a Legacy without severely compromising suspension geometry. I'll probably just lower it an inch or two in an attempt to get the CoG down a bit.
Tires will be 255 or 275, whatever I can fit. Probably something in the sub-200 treadwear range since I don't have to daily drive on them. Unlike the Fiero, which has room for 2 or 3 tires, the Outback has enough cargo capacity to carry two whole
sets in the back on the way to and from the track, with room leftover for tools and a passenger or two.
Question
Besides bushing compliance (which has no easily reversible solution) and chassis stiffness (which I plan to add bolt-in braces for), are there any other concerns with running absurd spring rates on a stock chassis?