Very frustrating update - having paid for and tried multiple spring lengths along with helper springs I've concluded that its just not possible to use a linear spring with these dampers without causing other issues.
Due to the damper design maybe being too long that it gives the following issues:
- a 450 pound 7 inch spring requires a helper spring to get a good ride height, however this the spring perches are obviously not designed for this in mind as the helper perch and spring perch come into contact as you can see
- Also at the ideal ride height there is only half an inch of bump travel.... which is 1/8th of the dampers travel which is very detrimental and may even be un-driveable. Raising the car to half about 50% of total travel for bump which is the minimum you would want really makes the ride height so high it may as well be an off-roader build instead. You might be able to see from the pics how high it is, although in real life it looks way worse!
So yeah the resulting options are....
- use a very very soft linear spring, that will give a consistent feel, allow for more camber but be way too soft on the track
- use a stiffer linear spring, that will give a consistent feel, allow for more camber but have almost no bump travel
- use a stiffer linear spring, that will give a consistent feel, allow for more camber but very very high ride height and then high CoG
- continue to use bilstein springs, that are overly soft before being loaded up on turn-in and only allow the car to a max of -2.3 deg camber but allow for a ideal ride height and so a much lower CoG
So in my opinion the only option is to continue to run bilsteins, pretty crappy result after all the effort and money I've put into this.
This article sums up the fundamentals well here, although took me some time to really grasp some aspects and do some other research on top
https://suspensionsecrets.co.uk/coilovers-installing-and-setting-ride-height-correctly/.
I know a lot more about suspension than I did a month ago but left feeling quite deflated after wasting quite a number of hours of taking the suspension on and off and wasting a good chunk of money over a spring and solid top mount collection....
So I think next I will refit the bilstein springs, sort out some better brake ducting and get the thing booked into retro resus then for a few jobs:
- rear control arms refurbished and bushings changed ( I took some of the arms off the other day, bushings are awful and I cannot be bothered with doing it myself now)
- ditch the aircon and majority of air bags
- corner weight
I was going to switch to a Varley red top battery and get it relocated towards the rear of the car with an internal cut off switch but think I may just look to save some cost for now and maybe stick in a basic toyota aygo battery or something for 40 quid off of ebay as a quick cheap solution for now that still saves 7+kg.
If anyone does want a brand new set of Compbrake top mounts, or even any length of 450/375 pound springs, let me know.