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Blow By Meter
A Blow By Meter can tell you exactly how much blow by is occurring inside your engine. The flow meter allows you to measure blow by from any engine speed, all the way from idle to wide-open throttle. A blow by test measures the volume of gases that are entering the crankcase past the piston rings.

Blow By:
What is blow-by? Blow-by occurs when the explosion that occurs in your engine combustion chamber causes fuel, air, and moisture to be forced past the rings into the crankcase. Your engine’s rings must maintain an excellent fit in order to contain the pressure. As rings and cylinder liners wear away they are less capable of maintaining this seal. Consequently, as a car ages the amount of blow-by that occurs could increase. Soot and deposits left over from incomplete combustion that collect on the rings can also inhibit their seal worsening blow-by.

Blow-by inhibits performance because it results in a loss of compression. When the expanding cases slip past the rings, they cannot as effectively push the piston down and make the vehicle go. This will result in less horsepower and a loss of fuel economy.

Detergents and Molybdenum
When the fuel, air, and moisture slip into the crankcase, they contaminate and dilute the oil in the crankcase. Among the many gasses in your compression chamber are unburned fuel, moisture, sulfur dioxide, and soot. Once these gasses slip into your crankcase they can dilute into your engine causing great damage. The detergents and Molybdenum Disulfide work together to clean the soot and deposits off of your rings allowing them to better seal the combustion chamber. The Moly fills the crevices in the cylinder walls providing a better seal.

J-TEC blow-by meters
J-TEC blow-by meters provide all the advantages of vortex shedding flow meters, in a design that is perfect for rugged applications, such as engine dynamometer testing. The VF563 is the flow meter of choice for measurement of crankcase blow-by gases in engine emissions testing applications. Measuring the flow rate of blow-by gases as they flow out of the crankcase vent is an effective way to monitor piston-ring sealing, lubricant performance, and crankcase ventilation systems. The J-TEC design incorporates a small strut, which offers minimal flow restriction, for high accuracy over an extended range. Each meter is individually calibrated to NIST traceable standards. J-TEC blow-by meters have no moving parts, so they are rugged and trouble-free.

Blow-By Test
A blow-by test requires a blow-by meters. The meter measures airflow, and is attached to either the crankcase vent on the valve cover breather or the PCV valve fitting. On a V6 or V8 engine, the opening on the opposite valve must be temporarily blocked so all the airflow from the crankcase will flow past the meter. When the engine is running, all blow-by that leaks past the rings will flow through the crankcase, out the valve cover opening and through the blow-by meter sensor. The meter outputs an analog voltage signal that ranges from zero to five volts. The display can then be converted into units that show you the volume of airflow per unit of time. Most engine builders typically display the reading in cubic feet per minute (cfm), though heavy-duty engine builders more often use cubic feet per hour (cfh). One supplier of blow-by meters said contrary to what many people think an engine typically has more blow-by at idle than at higher rpms. As the speed goes up, the rings actually seal better and blow-by stops.

How much blow-by is normal for an Engine?
Dividing an engine’s maximum horsepower output by 50 ill give you a ballpark estimate for how much blow-by you would normally expect to see. For example, a street performance engine that makes around 500 horsepower will typically have about 10 cfm of blow-by with conventional piston rings and ring end gap tolerances. Higher performance engines that are built to tighter tolerances will usually have less blow-by, as might those with gapless piston rings. Less blow-by means more usable horsepower. Being able to baseline the actual blow-by in an engine means you can then go back and try different ring configurations, ring types (conventional or gapless), different end gap settings and cylinder wall finishes to see which combination gives the best seal and least amount of blow-by. Measuring blow-by has been on of the best kept secrets with performance engine builders because it allows them to see how well the rings are or are not sealing. It also allows them to detect any ring flutter that may be occurring within a particular rpm range, and to then change to mass or end gaps of the rings to minimize the problem.