I'm replacing the coil springs on my sm block 68 coupe. I will also be lowering the car 1" for better handling. The question is, should I buy 620# or 550# springs. Would like to hear some opinions. :scratch:

 

1"=620#

 

I used these and am very happy with the ride. You get the best of both worlds, a softer spring over those little bumps and a stiffer spring when you lean on the car diving into a corner. These are best used with a stiffer shock, KYB gas adjusts or even Koni shocks if you have the extra cash.

https://www.pro-motorsports.com/stor...il-springs.asp

 

go for the 1" drop 620 springs. just my .02

Richard.

 

I got the 720's and they are fine with GR2s
they are even better than the stock rusty springs!

 

DOES ANYONE KNOW WHAT THE SPRING RATE WAS FOR THE ORIGINAL COIL SPRINGS?

 

depends on the car, sixor v8, standard or auto, with ac or not, with ps or not, gt or base model, etc.etc etc.

generally anywhere from about 400-450 or so.

 

i JUST THOUGHT i'D ADD A FEW COMMENTS SINCE i JUST ABOUT COMPLETED installing 620 springs and tubular control arms, uppers and lowers. For the 620's, I believe you will want to replace the spring perches(saddles) as the originals are different. Also, if the bushings are old in the upper and lower arms, this is the time to do all of it. All very easy to remove, replace ball joints, etc. Even better though, you can get a template to relocate the upper stock A-Arm 1" lower. This won't affect the ride height as much as it will improve tire contact with the road. If you want to reuse the stock A-Arm, you can install a negative wedge kit which angles the ball joint to keep it from binding. All very easy. Nuts and bolts stuff. This is the Shelby mod. You sinply bolt the template into the existing upper control arm mounting holes, punch the new locations, and drill.

Jay B

 

Sorry, forgot to mention. I used the Global West kit. However, negative wedge and templates available from pro-motorsports.com as mentioned by a previous responder.

 

i put 620 1" drop on my 65 and i love them. made a huge difference. your mustang is heavier so it may be a lil differernt, but i thought i would give an opinion anyways.

 

I went with the 550# on my coupe. Great handling and I'm not beat up while just cruising. The actuall rate of a 550# spring is 480# and the actuall on the 620# is 580#.

There is an insert in the Mustang Plus catalog that outlines all the factory spring rates and actual verses advertised rates of springs.

 

I used 620 1" drops coils up front and 1' drop leafs in the rear on my 72 Grande Coupe and was very pleased. Waiting for it to get back from the shop after the alignment and tranny rebuild now. I have not driven it a lot since installing the new springs hope to know better how it turned out later this month.