I need a little advice here. The Demon weighs 3100 with a 53/47 front to rear bias. I currently have 110# springs on the rear. They sag a little. I want to increase the rear ride height a bit, but cannot go any higher on the perches/mounts. So, I think I could achieve what I want by taking a little of the sag away.

Previously, I called Bickel and he told me I needed 185# springs - there is no way I need 185s, so I bought 140s. I have a brand new set of Bickel 140s that I could put in, but before I do that - I want to ask - is 140 too much spring for the car?

Back half 4-link that now has coil overs in the front, 4.56 gear, 727, and 875-900hp NA.

If I could raise it a hair and perhaps get better performance as well I would be very happy.

So - I guess the question is: With similar cars, who is running what weight spring? And what is the right spring for me.

185

Remember you only need enough spring to hold the
body up so the shock is at its designed working
length, move the lower shock mount up to raise the body
EDIT
correction you should be using 120# springs now and
if you want to lift it(this is assuming you have adjustable
lower mounts) the 140# might be a bit much

The mounts are all the way up already - I can't go anymore. I could use the 140s I already have or order 120-125. But, they need to work as well.

Modify the shock mounts to get your desired ride height

The shocks are at the top mount setting. The shock mounts cannot be modified nor can I buy any with a different offset - these are single piece Alston's with the 6* angle. The springs are dialed to the normal position to maintain the desired eye to eye length. The car sags a good 1-1/2 to 2 inches if I pull up on my parachute mount.

So - is the 110 too light?

My car weights about the same and i have 130's and i think there to stiff, i was told to use 150's , you could jump on the back and it didn't move. u Unless your going to use it as a tow vehicle lol don't go 185's.

No - I'm definitely not going 185, I'm trying to figure out if:

1) The 110s are too light or correct.
2) If 110s too light, what is correct as I already have a pair of 140s sitting here

Think I have said this before but lets try again You have the 140's why not throw them on there and see what you get? Easy enough thing to swap out.

I think you already know this but just for a refresher. I have 110's in my heap at 2800, had 120's in the Valiant at 3470 and the old Duster had 110's at 3050. The Vega has 90's if that matters

My Challenger weighs about 3300lbs with me in it. I just changed the springs from 150 to 110. It did sit the rear down some but the car seems to work better. The car would unload the tire before and now it doesn't. How old are your springs is it possible they are sagging because they are old?

I'd say 130's, or 125's with xtra preload. I run 120# Eibachs with 1" preload. My Dart wieghs 300# less then your car.
Spring, shock and TIRE must be tuned to work with each other

All springs are not created equal...The spring rating may vary especially after time. I noticed you have them on an angle too which affects the rate as well. I agree you should 'try them'. Also, by raising the rear height you will decrease the bias front to rear. I'd just be careful to not top-out the shock now. Using the single adj. shock, I foresee suspension movement in your future.

I have Koni DAs on it and am well within the setting limits. The springs are the original Koni's and the angle is by design as it is an Alston CEII 4 link. Everything is planned out - it's the weight rating of the spring I'm thinking about.

I think I have said this a few times before but once more wont hurt.

ALL this stuff is just THEORY, be it suspension engine what ever. The only way to KNOW what will happen is to try it. You have the springs, toss them on and give it a try

140's will work fine. Listen to Al. Mike

I might make a suggestion, clean all of the suspension
points to make sure they arent binding. The 140
will be to stiff but try them since you have them.
This stuff isnt theory its math, the one thing that
I dont know on your car is the angle of the shock
to calculate that in ... the closer you get to 45*,
the closer you get to doubling the spring pressure

Well while I will agree that math plays a role in this equation there are no absolutes to it. That is one place you will certainly have an issue with the math theory. I have read Morgans book and sometimes it is just as simple as math. I consider the math a good starting point that will get you in the ballpark. After that you have to try different things to see what is optimal for your car.

Having a little more intimate knowledge of the car in question I think the 140's are worth a shot no matter what.