Quote:
Originally Posted by flatjack9
Engines used to run with full vacuum at idle. As emissions laws came in to effect, vacuum was changed to ported to help lower emissions.
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Some engines did. Some didn't. Ford always used ported didn't they? All the OEMs basically changed to ported though, when federal emissions laws were enacted, to reduce NOX. Retarded ignition timing, late valve timing, compression reduction. A real goat roundup.
They did make a concession and used a temperature solenoid to revert to manifold vacuum after it overheated, which wasn't uncommon because ... the ignition timing was retarded. LOL! (Never mind that the engine is now probably roached).