Are early coil springs shorter then later. I'm try to stuff a 76 SB w/air springs into a 71 frame and they seem long. Help?

 

My tock small block springs were 15 1/2 inches free length and measured 287 pounds per inch.

 

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Are early coil springs shorter then later. I'm try to stuff a 76 SB w/air springs into a 71 frame and they seem long. Help?

GM produced thousands of spring heights and ratings. In 71 four different ratings were produced and there was also a heavy duty rating for F41 suspension. By 76, Corvette still had four offered for base but the ratings were heavier because the cars got heavier. There was also FE7 which had its own set of HD springs.

Longer springs meants lighter rating...while heavy rating meant shorter springs. Tell me your options and I can give you a rating you can use to figure out where your going. What happens when one guesses is that the car is too high or too low.

Suspensions were engineered precisely and than adjusted for curb height with very specific heights. Hope this helps.

 

The car is a BB 4-speed convertible. I added alum. heads. I was thinking that I could use SB with air should be the same.

 

Your original springs were rated at 284 pr 325 lb/in or a sprung curb load of either under 777 lbs per wheel or over 777 lbs per wheel resp. A big block with A/C was probably the later (325 lb/in).

In 76, the ratings were different. You can see base started at 760 for a smallblock in contrast to the under 777 lbs for the big block spring. A smallblock with A/C would have bumped it up but without the specs...I'm not sure how much. Look at the stiffest spring offered in 76...936 lb/in! Pretty hefty. This is due to added weight from emission equipment, rubber bumper supports and shock units and other safety equipment.

A 76 AIM would give you specifics how to calculate...alum heads reduce the factor as you indicate. Your original springs were stiffer than what you planning to put in.

I've never done this but kits are usually engineered to provide balance to a suspension upgrade.

Under 760
761-800
801-845
846-935
Over 936

It's a tough call. You can try it or find someone locally that can assist you with the calculations to figure out if it will work for you...speed shops I guess should be able to calculate the differences. Let us know how it works.

 

Look at the stiffest spring offered in 76...936 lb/in! Pretty hefty. :eek: :eek: