Well this where the ignorance sets in. If the engine liked 25/35 at idle, it will be
making more HP [ because idle speed went UP ] at idle. The rpm will increase, the idle speed can
theeeeeeen be lowered to a value [ often lower than it was idling with 12* initial ] to provide a better idle with more vacuum. The trans can now be put into gear at a lower rpm...& with less rpm drop.
Vacuum is an indicator of idle engine efficiency at low rpms. Every wonder why that big cam will not idle under 1100 rpm......but the factory cam idles at 600 rpm....& with more vacuum?????
Increasing timing at idle from the nominal 12* increases vacuum.
Many GM cars had MVA from the factory & had well over 20* at idle with stock cams. My GTO left the showroom with 26* at idle & cam that had under 200* @ 050 on the intake.
Chrysler missed the boat.
Read this & learn:
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