As I recall Plus 4 Black Springs are 160 in/lbs
Plus 8 Blue Springs are 140 in/lbs
4/4 Eisbach springs are 120 in/lbs
To confuse You more Plus 4 Black Springs were used on +8's as well as +4's
The Blue Spring came on late model +8's and Roadsters. Many of these +8's were converted to the Black Springs for better handling. I have used the blue springs on My +8. Now using the Suplex kit. On My '61 DHC with Zetec engine I am using the Blue Springs. Zetec is lighter than orig TR engine. The 4/4 spring is a little longer than the +4 and +8 springs and a bitch to get into place even though that are softer springs.
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