1969 Charger 383 car How much arch should there be in the rear springs ?

[70 sublime]

The rear springs on my car are almost straight when the car is just sitting on a flat floor in the shop
Thinking about getting them re arched
Got snooping around on how it is done and they just get re bent one leaf at a time every 3 or 4 inches on a hydraulic press

We have a press in the farm shop and I do have an extra set of springs so think I might give it a try

So my question would be how much arch is in a set of springs when off a car if you measure a straight line between the center of the two mounting holes to the face of the spring ??

[375instroke]

Do you not like how high it sits, or the rake?

From the '69 FSM:

Measuring Spring Height
When measuring rear spring heights, vehicle
should be placed on a level floor, have correct front
suspension height on both sides, correct tire pressures,
no passenger or luggage compartment load
and a full tank of fuel.
(1) Jounce car several times (front bumper first).
Release bumpers at same point in each cycle.
(2) Measure shortest distance from highest point
on underside of rear axle bumper strap (at rear of
bumper) to top of axle housing.
(3) Measure both right and left sides.
If these measurements vary by more than 3/4 inch
(side to side), it is an indication that one of the rear
springs may need replacing.
It is normal for rear springs to show some reverse
arch, even with no load, so appearance alone should
not be reason for spring replacement.

[70 sublime]

My car has the rear springs almost straight
Someone has put longer shackles at the back to get the car to ride higher

What I am asking is when the springs are off the car with no weight on them what so ever how tall is the arch

If I try to re arch them myself I would like to know how much is enough without having to put them back on the car to find out

[birdsandbees]

Longer shackles are just an avenue to let the springs go flat, as they now have a longer span that they can flex out to!

[375instroke]

Long shackles are a recipe for disaster, along with overarched springs.  Are springs formed hot, then heat treated or quenched, or are they cold formed?  If you measure what they are now, and bend them so they are one inch more than they are now, wouldn't the car sit one inch higher?  You can't change the spring rate unless you change the temper (is this the correct term?) of the metal or add leafs.

[70 sublime]

https://www.youtube.com/watch?v=HImEhw1UUoQ

This is what I am thinking about

My springs seem to be flat
If I take them off the car how much arch should be on a new factory set of springs ?