Today I installed a new valve cover breather which has the PCV built in, I was not expecting the engine to respond differently to this change. I fired her up, and the idle was far better than ever before, even the exhaust tone sounded far better. If anyone has read any of my other threads I was having trouble with oil ingestion, this new PCV/Breather has almost completely removed the blue smoke, proving that I must have been sucking in oil through the PCV! Here's where it gets confusing though, If can hear the PCV ball jingling as the engine is idling, everything is amazing, my idle is actually 300rpm's higher! So now, when my engine is all up to temp ill pull the throttle quickly and hear one single pop, like a pencil tapping a wood table, but no hesitation, and it does not seem to be coming from the carb as far as I can tell. At this point blue smoke, though not much, will appear from the driver side exhuast and the idle will settle down 300rpm's lower than before, and the pcv/breather wont be making a jingling noise. With a couple more tries with the throttle ill begin to hear the pcv/breather jingling again, and at this point the idle will return to 300rpm's higher than normal. It's also interesting to note that when I turned the ignition off while I was in the cab, I heard the same pop again and it seemed to be from the passenger side of the engine (where my new breather is). None of these noises existed BEFORE I installed this new breather, but with the old setup my idle was 300rpm's lower and I burned much more oil. I have my theories, but I want to see what everyone else thinks first, hopefully if we can find the answer, this thread could be great help to others. The usual much needed Info: 1952 GMC P/U Rebuilt SBC 350 decking and rebore likely. Unknown very lopey cam 8in vac @ idle. Aluminum Street Dominator Intake. Holley 600, Mechanical Secondaries, Mechanical Choke. Rebuilt 462624 heads (crack-prone) decking and larger valves likely. PCV/breather passenger valve cover / K&N breather driver side.
The typical valve will cut most flow from the crankcase at idle. At part throttle or cruise with a drop in vacuum the valve opens more allowing more flow for better ventilation of the crankcase. This requires a breather on the other VC or if an older intake through the oil fill tube. A low vacuum at idle will not produce enough difference to pull the valve mostly closed. This will then create an uncontrolled vacuum leak. If the oil baffle in the VC is missing or damaged, this will allow oil/oil mist to be ingested into the engine, rather than just ventilating gases. If you have a PCV valve that is designed for a 'large cam' low vacuum idle you should be fine. Otherwise you will have an un-metered vacuum leak.
ohhhhh MAD MIKE I think you just hit it right on the button, I did not know that! I will begin my search for the correct PCV valve. thanks!
You may want to look at some factory hi-performance engines from the muscle car era that had lumpy cams and PCV valve. Possibly the '70 370HP 350 from a Corvette? See if that PCV valve is any different from the more 'mundane' 300HP 350 found in the '70 Impala.
I am unfamiliar with a combination breather/pcv valve. Who made it and what does it look like? I don't get it. Alden
http://www.jegs.com/images/photos/800/865/865-4284.jpg link to a picture, it's a Spectre 4284, just got it yesterday thought it was a cool design, makes the engine bay look a tad cleaner in my opinion
The purpose of the PCV valve and breather are to evacuate gas build up in the engine/crankcase from blow-by. Unlike a road tube or pair of breathers the PCV valve connected to engine vacuum acts as an active scavenging system which also helps with ring sealing. It's not just an emissions device, but can aide in performance. Dry sump oil systems have a similar effect on ring sealing. The added benefit is a cleaner engine, breathers and road tubes tend to leave a mess on the engine and car. Heh, I actually have that Spectre breather/PCV valve setup on an OT car. Works pretty good.
I had the exact same symptoms with my 302 Ford. rough idle(OK at upper RPM's),The PCV rattled at idle. Replaced the PCV valve, idle smoothed out and exhaust quieted down a bunch. Was basically a vac leak at idle.
I don't see why you have to get rid of it. The valve itself is a typical 60's-80's PCV valve design. You can replace that piece. Just need to find a unit with a softer spring that will work better with the lower vacuum. I thought Mr Gasket sold a unit that was more suitable for lower vacuum applications.
Yes if you add a PCV valve to a running engine that does not have one, the controlled vacuum leak (PCV valve) will require the adjustment of the idle mixture screws to richen the mixture for the idle.
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