Coilover specification

[trevorbrady]

I've installed the early aluminium 944 trailing arms on my project '03 after already removing the torsion bars to make room for the 915 box. Since I no longer have the facility of using torsion bars I have to use coilover shock absorbers to keep the back end up. I'm trying to get my head around the whole thing, and I've been reading old threads on the subject here. Can anyone tell me definitively what the length (open and closed) and spring rate should be for the rear coilovers so I can go and source some?

I took a quick measurement from my car and found that with the spring plate on its bottom stop (i.e. suspension in full extension) the measurement between the top shock mount on the chassis and the bottom shock mount on the trailing arm was close to 14" (approx 355mm). On full suspension compression (no rubber bumpstops, with the metal bumpstop pad of the arm touching the metal bumpstop pad of the chassis) the measurement between the shock mounting points was close to 10" (approx 254mm). I understand that I'll have to put in a rubber bump stop, so this compressed measurement will become larger.

So I'm looking for shocks with a range of 14" fully extended to 10" fully compressed. Should I look for shocks with an upper limit greater than 14" to have some preload on the springs? Are the springs on coilovers progressive? Do they get harder with more compression?

What spring rate is good for a stock 1303 rear end? What spring rate is good for a 1303 with a heavier Subaru engine?

Any information would be gladly received. I'm trying to establish some facts before I go and order the wrong parts...

[ricola]

Hi Trev,
I used 15" extended, 10" compressed AVOs, with a 12" 300lb spring in the speedster. I would guess go up a bit on the spring rate but that should give you a fairly good idea of where to start...

Rich

[trevorbrady]

excellent info! Thanks Rich!

[ricola]

Forgot to say, the coil-overs are for the 1.9" springs which are needed for the steel arms (for clearance) but you may be able to get away with 2 1/4" versions with your ally arms and springs are easier to get with higher ratings...

Rich