Originally Posted by neverending
I know there's been countless posts and I've read most. However it seems crazy to me, I have what amounts to one of the most common set ups in rodding. TH350 /350 290HP /600 holley. Your entry level basic motor albeit a wheezy low compression duff cam motor. I have managed to make it almost fly considering what it is,but I have one or two unanswered problems. Everyone has an opinion and I'm looking for the definative answer to this question. Currently running open breathers on both rocker covers, venting to atmosphere. Introduce PCV and the carb is naf. Cant use exhaust evacuation , too much back pressure. Yesterday the guy I bought the engine from said run pipe from both sides and T into the air filter. Does this sound ok?
Are you driving on the street or racing this?
Basically a new 290 horse 350 should not have so much blow by that crankcase venting is a problem, at least for the street. If this is pressurizing the crankcase to a point a force can be felt when the vents are covered with your hands or to where oil smoke is issuing, then one needs to consider an internal failure.
For the street PCV is the way to go, it insures that combustible gases present int he crankcase are cycled into the combustion chambers and burnt. Venting one side back to the air filter insures both that the crankcase gets clean filtered air to replace the fumes draw out by the PCV and that for a street engine that occasionally sees WOT, where the PCV doesn't function, that there is an alternative path to eliminate crankcase vapors via being sucked into the carb's air horn.
Street engines with Positive Crankcase Ventallation systems far outlast those without. PCV systems are extremely good at getting rid of vapors that left to condense in the crankcase cause considerable corrosion damage to intenral engine structures, and develop sludge and varnishes in the lubricating oil.
A vacuum exhaust system is only required on a competition engine or a super charged engine where the crankcase is under so much blow by pressure that there is not other way to provide sufficient amounts of venting without also putting a pump on the crankcase. Such systems require an oil separator to trap liquid coming out with the vented gases.