Help on springs

I have built a square tube chassis under my Falcon.I am now trying to figure out what rate(pound) spring I should use.I built it based off a mustang II style front end.The springs that I have in it now are 400 lb. Springs.They came with the shocks.With these springs and dummy engine and trans in car,it won't compress at all.I know I need some lighter ones,but how much lighter is my question.Anyone ever done this before or have a deal similar to mine?---RED

what lenght spring and shock combo? we were told on my buddies 65 falcon with rod n customs kit under weight the lower control arms should be level with the ground. also we were told on a shock that has 3" of travel...we should have 1" of compression and 2" of rebound. we have not bought the shock combo yet, but we were leaning towards the 400 pounders ourselves. stock front rails, MII..towers removed, square tube chassis,347" C4. Our friends 65 stang has 400 lb springs with a 418" windsor and it is just fine. Takes 400 lbs to colapse spring 1", is your dummy engine a complete?

forgot to add...the 400 lb springs that we are using are 8" long, when I had foxbody struts under my car I had 250 lb springs that were 14" long with a big block...512 Fairlane on here has my springs that he will use on his set up....Jason

'65 T-BOLT wrote:what lenght spring and shock combo? we were told on my buddies 65 falcon with rod n customs kit under weight the lower control arms should be level with the ground. also we were told on a shock that has 3" of travel...we should have 1" of compression and 2" of rebound. we have not bought the shock combo yet, but we were leaning towards the 400 pounders ourselves. stock front rails, MII..towers removed, square tube chassis,347" C4. Our friends 65 stang has 400 lb springs with a 418" windsor and it is just fine. Takes 400 lbs to colapse spring 1", is your dummy engine a complete?

It's a 8"spring and shock.As far as the dummy engine,it's a bare block.My lowers aren't parallel with the ground yet,but are very close.I'll add a little more weight to it since I don't have the crank,heads,intake and front dress on it and see what I have then.Thanks for the input.---RED

Red Here is a guide that I think will help you.The first thing you should do is to determine what the exact corner weights of your car will be (left front, right front, left rear, right rear) with the car at race weight (including the driver weight, fuel, oil, etc.). Spring rates are determined by the amount the spring deflects versus the weight placed upon it. As an example, a 250 pound spring rate is a spring which will deflect 1 inch for every 250 pounds placed upon it. This sounds simple, but there's more: The actual suspension geometry can influence how much the spring deflects. You have to compensate for the geometry when determining the correct spring rate for your car.


Gross Vehicle
Weight (lbs)

Front Spring Rate Rear Spring Rate
(lb./in. approx.)

2000 185 85
2350 200 95
2500 215 120-140
3000-3500 250-350 150-200