Right, I know about anti-dive and how to build it in to front suspension, but I have an issue that has just reared it's head.
Under heavy braking in a short distance, I heard a scrape under my nose cone !
This may have also been helped by a less than perfect road surface.
Will raising my spring rates on my front suspension slightly help stop this?
My design weights by the sva were 550 Front with driver, but both my springs are 250 each.
Will raising them to 350 improve this?
I did have to wind the springs in a long way to get my ride height set, maybe a little too much on the 250 lb springs?
Remember I have inboard suspension and wishbones nearly twice the length of a 7 so comparing actual rates will be different.

250 - 350 seems quite a change. Maybe a longer set of 280lbs would solve things? You don't want to over do it and get horribly stiff suspension.

This may be silly but why not first try stiffening up you front shocks a bit if you have spare adjustment - I know it wont stop the nose diving but it may just slow it down enough to help.

I agree with Nitram38 that a 40% increase in spring rate sounds is a little over the top - the other option is to fit longer bump stops if possible. (a much cheaper option than changing springs)

Mulling over your problem further I think you should ask yourself if the current springs provide a good compromise for ride and handling. If they do don't mess with what works just look at longer more compliant bump stops or stiffening up the shocks.

[Edited on 8/5/07 by Ivan]

I had a similar problem and stiffened up the dampers a tad - less grounding under braking and rough roads now, in fact better handling too

I have tried increasing the damper settings but this has not stopped the dive. The max spring length on a 12" shock is 8" (what I have now).
My reasoning for 350lbs is that I had to wind the springs up a lot to get the car to sit and work properly.
Maybe a stronger spring will mean that I don't have to compress it as much?

if you have inboard suspension, why not try modifying your rockers to make it rising rate, should technically be possible to make it not hit the deck even with no springs at all!

It's cheaper, easier and quicker to change the springs thanks

DIY Si has got it about right try 280 to 300 springs and that should sort it out going by your figure of 550/350 f&r respectively.

Something told me to go with 350 and I have fitted them.
The suspension works well in that I can jump up and down in the car and I can feel the springs working. Before it just sank and only returned very slightly.
I can now reduce my shock settings.
I need a good dry day to give it a blast.
Initial impressions are that my braking seems more positive.

I gave the car a good blast today and the front end is transformed!
Instead of excessive dive, I only get a little (depending on what speed I brake from) and the brakes stop on a sixpence.
Going over rough roads used to have the car bouncing about (up and down, not bumpsteer). Now it seems to just skip the bumps.
No more loose fillings for me!