PCV Valve ratings
jamyers
09-18-2008, 08:34 PM
Does anybody know where I can find info on how various PCV Valves are rated (vacuum opening and flow rates)?
Blue Bowtie
09-21-2008, 12:06 PM
RobertShaw has detailed information about the calibrations of their PCV valves designed for various applications.
I worked at a plant where pintles and housings were manufactured for their PCV valves, and the component parts required constant SPC testing to assure the assemblies were within the allowable tolerance for PCV flow at specific vacuum. The flow is NOT linear. There is relatively low flow at moderately high vacuum (about 18-20" Hg), higher flow as vacuum decreases closer to 10" Hg (engine load increases) and flow tapering back toward zero as vacuum drops even further (below 7" Hg). The starting point for flow was also critical.
Whether RobertShaw would release that information is a completely different question.
I have encountered situations where an engine has had a non-stock cam lobe profile, altered valve timing, larger than stock intake runners, enlarged valves, and oversized throttle bodies. These factors can create a need for a non-stock PCV flow and different starting flow rates. Right or wrong, I have had moderate success installing PCV valves intended for smaller displacement engines. These valves commonly allow for adequate flow at medium vacuum to help capture blowby gasses under load, but still flow less at high vacuum so that idle is not affected as much. Stock PCV valves tend to flow too much at idle for a modified engine and make fuel trim at idle a real challenge.
I worked at a plant where pintles and housings were manufactured for their PCV valves, and the component parts required constant SPC testing to assure the assemblies were within the allowable tolerance for PCV flow at specific vacuum. The flow is NOT linear. There is relatively low flow at moderately high vacuum (about 18-20" Hg), higher flow as vacuum decreases closer to 10" Hg (engine load increases) and flow tapering back toward zero as vacuum drops even further (below 7" Hg). The starting point for flow was also critical.
Whether RobertShaw would release that information is a completely different question.
I have encountered situations where an engine has had a non-stock cam lobe profile, altered valve timing, larger than stock intake runners, enlarged valves, and oversized throttle bodies. These factors can create a need for a non-stock PCV flow and different starting flow rates. Right or wrong, I have had moderate success installing PCV valves intended for smaller displacement engines. These valves commonly allow for adequate flow at medium vacuum to help capture blowby gasses under load, but still flow less at high vacuum so that idle is not affected as much. Stock PCV valves tend to flow too much at idle for a modified engine and make fuel trim at idle a real challenge.
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