hi all, currently rebuilding my front strut setup and have some queries for those that have done these conversions before.
start with what i've got-
shortened stanza strut with a koni sport insert. coilover thread platform with home machined lock/spring mounts. coil over spring and vb commodore adjustable strut tops. This was pre setup before i bought the car but the struts fell out of the towers when i was replacing the steering so time to replace.
started out just going to replace the tops with new nolethane tops(already got them) but realised the inserts were shagged. so i went to pull the insert from 1 strut but no go, super tight!
(had to cut 1 in half to get the insert out) i now have 2x200b struts to make fit. my questionis if using the coilover setup the insert should have enough throw left to support the spring at the lowest point without bottoming out, and wen fully raised on the coilover thread should not compress the spring...to much?
That would make sense to me but then im no suspension expert. what height should the struts be to fit nicely? my modified setup is 560mm. in theory i could raise it up but the strut insert is fully extended and the platform is at the bottom..

Are u going to finish the car now? still have the simmons?

You might need to make your questions more clear.

1. If you've shorten the shock by half, you need to double the spring rate to stop it bottoming out.

2. The spring should be captured at all times. This is done either using a progressive spring or a tender/helper spring.

3. The shocker insert travel needs to be greater than the sum of the gaps in the spring coil.

4. The spring should never be able to completely compress, otherwise you risk breaking the spring, or more likely pushing the strut tower through the bonnet.

5. The shock bottoming out is also bad, and should only occur when maybe hitting a pothole.

For a street car with a 200mm long spring (shortened strut) on the front of a 1200 I would be recommending a 250-350 pound spring to stop the car from bottoming out within the 3 inch shock travel. I use a 200mm 200 pound spring (+helper spring) on the front of my 1200. It rides ok on the street but it bottoms out too easily. I am saving for a set of 275 pound springs of the same uncompressed dimensions.

that does clarify a few of my thoughts, in theory i def need a longer insert to get the travel right. the spring rate should be up there, pretty sure they are 260lb.

shortcoupe, yeah i've still got it, getting it together slowley. got the simmons still, goto get smaller treads for them tho. Diffs getting done atm. really want to get it rolling. few mates getting cars together aswell so i don't want to be left out!

It's fairly easy to estimate how much your spring will compress using the spring rate and a rough corner weight estimate. Add a little to the corner weight estimate (about x1.1) to allow for the strut being at a shorter moment arm than the wheel in relation to the cross member. Divide your adjusted corner weight by the spring rate (use same units obviously) and this will be the compression of the spring with the weight on it. Subtract that from the starting length to give the spring length with weight on it.

You then need to have the strut in the car with a wheel on and lower it into position and measure from the top hat down to work out where your bottom perch needs to be to get that static ride height.

It's crude but has worked several times for me.