Hilltop Workshop | Vacuum advance discussion. Factory ported vacuum on a 1961 T-bird.
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- āđāļāļĒāđāļāļĢāđāđāļĄāļ·āđāļ 3 āđāļĄ.āļĒ. 2021
- No biggie, but just demonstrating that ported vacuum has been the way for many, many cars for decades, from the factory.
I sincerely hope you guys find this useful. ð - āļ§āļīāļāļĒāļēāļĻāļēāļŠāļāļĢāđāđāļĨāļ°āđāļāļāđāļāđāļĨāļĒāļĩ
There were exceptions of course! but your guy was right, ported vacuum from around 1971 USA was to lower Nox emissions at idle . ..that's a fact! Manifold vacuum has the most history.
Good video. Ported vacuum WAS used for ignition advance on many cars as early as the 40s. The thunderbird uses ported because its set up to use ported. Part of the "set up" is a dist that has the correct springs/weights for ported. Full manifold requires a faster advance in the dist. Picking some year like 1969 and claiming thats the cutoff from "performance" with full man vac to "emissions" with ported is a gross over simplification. Also, copy pasting other people's comments into this line of dialogue is cheap chicanery. Keep up the good work on explaining vac advance for dummies.
So the EPA or whoever forced car manufactures to use ported vacuum for vac advance timing because at idle in the city the mixtures/ emissions where too high in city/traffic driving conditions. (Manifold vacuum had too rich mixture at idle in their opinion) so they leaned it out at idle by adding more air. (less NOX) But these changes raised idle rpm to aprox 3,000! rpm compared to the standard idle timing/rpm settings. So to fix that what did they do? They Retarded the timing. For example 10-15 degrees BTDC to just TDC. (check any workshop manual of the day.)
These changes, modifying the vacuum advance system etc, is why they switched to a timed/ported vacuum source on the carburetor instead of manifold vacuum, for our distributors. So vacuum advance only operates above the throttle blades off idle.
And our cars performance suffered because of this along with lowering the compression ratio! Thank you EPA!
I just noticed, that engine isn't running vacuum advance, the hose is cut off.. Lol
You mean, the hose that I temporarily disconnected to attach my gauge?
Take a breath, brother... :/
Take a closer look. Thats the normal tbird metal tube coming from the ported vac advance port from the passenger side of the venerable autolite 4100 4V right in front of the choke. That port is not full manifold vac. Come on!