racerender intake manifold pressure object

Compared to consumer-grade instruments, a professional-quality mechanical vacuum is accurate, responsive and produces repeatable results. Intake manifold vacuum can be measured with a mechanical gauge, electronic pressure transducer, or through the engine management system via a diagnostic scan tool. In most cases, highly efficient, electronically controlled engines produce a slightly higher vacuum reading than do mechanically controlled engines. Most, for example, advance the spark timing and lean the fuel mixture to the point of misfiring at idle speeds. In most cases, fuel economy would improve because the carburetor’s power enrichment system, which normally begins to open at 6.4 to 8.5” Hg, remains closed with the higher vacuum achieved by precision tuning.Įlectronic engine management systems essentially follow the same strategies, but with much tighter parameters. To adjust the idle air/fuel mixture, the technician would adjust the mixture screw to achieve maximum intake manifold vacuum and then open the adjustment screw one-quarter to one-half turn more to compensate for temperature and barometric pressure changes. In many cases, a skilled technician armed with an accurate vacuum gauge achieved optimum spark timing by advancing the spark timing into misfire and then retarding several inches of mercury to achieve a smooth idle. In the heyday of the mechanically managed engine, skilled mechanics carefully adjusted spark timing and air/fuel ratios to balance the highest vacuum reading against the smoothest idle quality. Similarly, the air/fuel mixture reduces intake manifold vacuum when it varies from a stoichiometric mixture to a rich or lean mixture. As the cylinder reaches maximum compression, the rate of combustion increases because the compressed air/fuel molecules ignite very rapidly. The base spark timing is normally advanced to allow time for a flame front to propagate from the spark plug into the combustion chamber. Complete combustion of the air/fuel mixture is achieved when the fuel mixture is ignited a few crankshaft degrees before the piston reaches top dead center (TDC) and before maximum cylinder compression pressure is reached. Due to the volume of air flowing around the throttle plate to maintain idle speed, the sea-level pressure differential or “vacuum” is normally reduced from 29.5” Hg to about 18” to 22” Hg at idle on a well-tuned engine.Īt the most basic level, peak cylinder pumping efficiency, idle speed power output and combustion efficiency go hand-in-hand with peak intake manifold vacuum. When adjusted correctly, the throttle plate will allow the engine to idle at a base speed of about 500 rpm.

With the exception of electronically controlled valve train systems, the idle speed of all other fuel-injected spark ignition engines is managed by a precision-machined throttle plate mounted in a precision bore. Since local weather conditions may cause atmospheric pressure to vary from standard, the current reading is usually referred to as “barometric pressure” or “baro.” Atmospheric pressure at sea level will also support a column of liquid mercury (Hg) 29.92” in height. A more current term refers to the pressure inside the intake manifold as Manifold Absolute Pressure or “MAP.” As currently used, the terms “pressure differential,” “MAP” and “intake manifold vacuum” refer to the difference between atmospheric and intake manifold pressures.Ītmospheric pressure is about 14.7 pounds per square inch of pressure at sea level. Technically speaking, the intake manifold must contain enough liquid fuel and air to support combustion, so what we have is not a complete vacuum, but an atmospheric “pressure differential” between the inside and outside of the intake manifold. Intake manifold vacuum analysis can be a little tricky because the conventional term “intake manifold vacuum” is a technical misnomer.

Racerender intake manifold pressure object