usually the TiAL spring rates coincide with engine idle vacuum.... so figure out where your engine idles at and buy the corresponding spring...
Engine Vacuum Reading / Color Use Spring
Between:
- 22 and -23 in/Hg -12 Psi (-24 in/Hg )
- 20 and -21 in/Hg Pink -11 Psi (-22 in/Hg )
- 16 and -19 in/Hg Un-painted -10 Psi (-20 in/Hg )
- 12 and -15 in/Hg White -8 Psi (-16 in/Hg )
- 8 and -11 in/Hg Black -6 Psi (-12 in/Hg )