1985 IROC w/ air. Rebuilding front suspension. Want to replace the coil springs during process. Stock replacement coil spring part numbers needed.
While I am asking- does anyone know the specifications of a stock IROC front coil spring?

 

88913422 Gm

 

From the lowering 101 thread the replacements from Moog are 5662 fronts, 5665 rears.

 

Are IROC springs stiffer?

 

Stiffer than some; less so than others.

Stock, new, 30 yrs ago, the OE ones were around 450 lbs/in. 5662 is a good bit stiffer than that, in the high 500s if memory serves.

The OE IROC are the stiffest ones that came on these particular cars. However there are MUCH stiffer springs that will "fit" (same OD, same end types, etc.) but came on other vehicles besides these. Just because they "fit" does not mean that you would ever want to use most of them though.

5662 is the most direct replacement available. Be aware however that the OE crap will have sagged DRAMATICALLY in the last 30 years, and because they are now SO wore out and the rears are even worse, installing them will LOOK LIKE you just RAISED the car about a foot in the front, although in fact all you did was restore it to factory-new ride height. Kinda like, people buy "lowering" springs, and I guess think that they're supposed to just open the box and pour whatever comes out all over their car and it will just magically jump itself closer to the ground; but IN FACT, many springs marketed as "lowering" will also RAISE the car from wherever it happens to be drooping to with its old wore-out sagging collapsed OE garbage.

Be warned.

Buy & install a set of either 5665 (constant rate) or CC635 (variable rate) at the same time.

5664 also fits and works, and is about 740-some-odd lbs/in.