The carburetted versions feature an unusual Weber 28 / 30 carb ( replacing the unreliable Ford VV unit ) with a manifold vacuum-actuated secondary choke, instead of the more usual sequential linkage which opens the secondary butterfly at 3 / 4 to full throttle.
42.
Auto enthusiasts have traditionally installed additional gauges such as manifold vacuum, battery current etc . The OBD standard interface has enabled a new generation of enthusiast instrumentation accessing the full range of vehicle data used for diagnostics, and derived data such as instantaneous fuel economy.
43.
For example, the position of the contact breaker points relative to the engine angle can be changed a small amount dynamically, allowing the ignition timing to be automatically advanced with increasing revolutions per minute ( RPM ) or increased manifold vacuum, giving better efficiency and performance.
44.
The research psychologist Gary Marcus's book " Kluge : The Haphazard Construction of the Human Mind " compares evolutionary kluges with engineering ones like manifold vacuum-powered windshield wipers when you accelerated or drove uphill, " Your wipers slowed to a crawl, or even stopped working altogether ."
45.
Manifold vacuum varies depending on engine load and throttle position, and automobiles use vacuum reservoirs or " vacuum canisters " to provide a usable source under varying conditions . super charged engines do not always produce vacuum; the intake manifold is actually pressurized when the turbo is spinning above a certain speed.
46.
The white area on the left side of the scale shows manifold vacuum under normal driving conditions, the short white dash is atmospheric pressure ( engine off ), the orange scale is where there is safe turbo bar where the wastegate may be opened or a fuel cut due to knocking may occur.
47.
Let me quote a passage : " The secondary spark control diaphragm ( fig . 12 ) forces a quick, momentary spark retard while the distributor vacuum line, carburetor vacuum passages and primary spark control diaphragm are normalizing to the new pressure conditions which develop when the spark control valve closes the manifold vacuum passage in the carburetor ."
48.
Motivated by government regulations mandating reduction of fuel consumption ( in the USA ) or reduction of carbon dioxide emissions, ( in Europe ) passenger cars and light trucks have been fitted with a variety of technologies ( downsized engines; lockup, multi-ratio and overdrive transmissions; variable valve timing, forced induction, Diesel engines, et al . ) which render manifold vacuum inadequate or unavailable.
