The best replacement for manifold is ported vacuum.

The best alternatives to manifold are rated as following:
★★★★★  ported vacuum
★★★★  headers
★★★★  header
★★★  ported vacuum advance
★★  manifold
★★  arcgis
★★  false bottom
★★  head gasket
★★  braid
★  many fold
★  skunk2
★  exhaust manifold
★  arcview
★  non manifold
★  air in head
  steel braid
  ported vacuum for advance
  skunk2 intake manifold
  thorley headers
  gasket
  b16 manifold
  tubular manifold
  inlet manifold
  qgis
  ported vacuum for vacuum advance
  ported
  tubular
  d16y8 manifold
  ls1
  equal length

Your alternative for manifold is not listed? Suggest!
Speaking about manifold, one probably shouldn't forget about catalytic converter.

Other search terms related to manifold and their ratings are:
★★★★★ catalytic converter
★★★★ egr
★★ pex
integrated catalytic converter
You have in mind a companion for manifold and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of manifold in all years. Click on graph for more.
manifold
ported vacuum
headers