Quote:
Originally Posted by Christ
It's not really a problem, that I've ever seen... this is why we have catch cans, oil separators, and vacuum valves (they're like BOV's, but in reverse).
Catch can keeps fluid oil from venting to atmosphere, oil separator keeps vaporized oil from venting to atmosphere, and vacuum valves will automatically close when vacuum reaches a specified level, e.g. 5", if that's what you want.
Simple A/C clutch would stop the pump (if belt driven, as on NHRA engines) from removing atmosphere until the vacuum valve opens back up. Poppet closes, vacuum pump shuts down, poppet opens, vacuum pump clutches up and turns back on. This would keep you closer to your required vacuum level in the block, easily.
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I get to hear about these problems all the time. Catch cans are not all created equal, that's for sure. Oil separators are easily overwhelmed by foamed oil -- this includes dry sump tanks if the system is not designed with enough reserve. Vacuum relief valves obviate the need for the Mad Max clutch -- though that would be cool. Make sure the relief valves draw in filtered air. Try to draw the vacuum from a properly baffled port in the block versus the valve covers. This is not always practical, of course.