[Nova Research Project]

Short version for the record:

69 L78 HD F40 had BK coded 5 leaf springs 100 pound rate(Listed as RPO on the spring calculators)
69 L78 Special Purpose F41 (springs and shocks only) had BG coded 4 leaf springs 125 pound rating (listed as HD on my spring calculators on my site)

In 70 they renamed the Heavy Duty F40 to Special Suspension and the F41 was called Sport Suspension and added the rear swaybar late in production, however they were the same springs as 69.

But yes springs were computer selected base on weight and options. That is why the LT1 used the BK 5 leaf as its F41 Sport Suspension vs the stiffer BG 4 leaf. The lighter block yielded over all less weight and required a lighter rated spring.

Both the 69 and 70 spring calculators are on the projects section of chevnova.org.

Greg