Spring rates for KVA cortina front end

Marcus

Supporter
Hi guys... own a humble KVA/KCC with a standard Ford Cortina Mk4 suspension.
Just bought her and the ride is truly awful. Front end dives under braking and pot holes with current coils springs. Have gone on Ford sites re heavy duty coils and found a pair rated at 275lbs each standard height for the old V6 Mk5 Cortina. I can't seem to find any stiffer so I was wondering if any KVA owners out there had any advise for this basic of basic front ends. Much appreciate any help.
Kind regards

Marcus
 

Dave Bilyk

Dave Bilyk
Supporter
Hi Marcus, mine is a DAX, but I had the same issue with 200lbf/in front and 250 rear. I increased to 300lbf/in front and 350 rear and that was great for road use on my car. If you measure inner diameter and free length of your springs, then have a look on the the site Mike provided, you should be able to find higher rates that will fit, just look for what fits, as you constrain choices if you look based on car make. If you are looking for road use, based on how mine feels I would keep below 350 at the front.
https://www.gt40s.com/threads/rear-brake-upgrade-for-dax40.17572/#post-187724
 

Dave Bilyk

Dave Bilyk
Supporter
Hi JP, these are the notes I made about my springs. Mine is DAX, but I believe same as GTD, so not necessarily match KVA.

As found

Front 200lbf/in 2.25"id 10.5" 10.5mm wire 10.5 turns

Rear 250lbf/in 2.25"id 10.5" 11 mm wire 10.5 turns



Bought

Front 300lbf/in 2.25"id 10.5" 11.5mm wire 10 turns

Rear 350lbf/in 2.25"id 10.5" 12mm wire 10 turns



Measured frequencies

Front 2.5Hz Rear 2.7Hz

So spring rates to make 3Hz are 432lbf/in F&R



From an estimated weight of 1200kg, and a F/R distribution of 45/55, current effective rates are F 380.2lbf/in R 542.2lbf/in
 

Terry Oxandale

Skinny Man
I'd like to understand what the reaction difference is between the two different length springs with same spring rate. Obviously the wire diameter is larger with the shorter spring (greater number of coils), but at the wheel, how does the wheel see this difference (other than the limited wheel movement with the shorter spring?
 
On mine I had 14" springs at the back but they had 2" preload (open lenght between the spring seat is 12") so how does this influence spring rate? or is this ride height only as well? (just curious, try to learn something)
 
btw marcus can you make the shocks (dampers) stiffer so it does not dive on the brakes so fast? this is what I was told to do to find the correct damper setting, start soft brake watch the nose dive, ad 3 clicks (out of 22 for full range) and test again till I am happy with the nose not diving so much. I have 400lbs on the front with 400lbs corner weight but my springs are at an 50-55 degree angle.
 

Dave Bilyk

Dave Bilyk
Supporter
JP, yes the spring length is in my response although not labelled, it's the 10.5" figure after the id.
Dave
 

Marcus

Supporter
Thanks for all the feedback guys and apologies for delayed response... I believe the 275lbs coils should be OK for road as the old KCC set up has the Cortina springs in a quite upright position therefore should be as stiff as a more modern GT set up with coils at say 50 degrees....that's my basic engineeting understanding anyhow. ... Now which shocks to buy...? Single tube, twin tube, alloy or steel all rather confusing. .. Car will mostly be used for road so looking at the GAZ adjustable....any input much appreciated as always. ..
 

Mike Pass

Supporter
Hi Marcus,

I have Protech. They are coil overs but you just need the shock so leave the spring platform off. Check the diameter which will fit on the car. -the 1.9" diameter should fit anything. Use 2.25" if space. Specify which end fittings you want to fit your suspension. Measure up for the open and closed lengths and also what the standard ones on the car are (allow for the rubber bump stops). Measure up after you put the new springs on - the ride height may well be different with the new uprated springs which are not adjustable via a spring platform. Measure twice - buy once!

Protech

https://protechshocks.co.uk

Or Avo

http://www.avouk.com/Products_TELE_TWIN_TUBE.htm

Cheers
Mike
 
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