MIKE H

When I last refreshed my engine my builder installed a PCV valve on it and I have a question concerning the install.

I have a 540 big block to start. Between the carb and the Dart intake I have a 3/4" four hole spacer, under that it has a 1" single hole spacer. I have Imco Rocker covers with the four 4" vent stacks, two stacks on each. We drilled about a ½" hole in the back centre of the lower spacer and installed a hose nipple in it, the hole lines up under the cross that is formed by the four holes in the upper four hole spacer. A hole was also drilled into one of the vent stacks on the rocker covers and the PCV valve was installed into the vent stack with a hose connected back to the nipple in the spacer.

My question is should I seal the tops of all four vent stacks so as to create a vacuum in the block, or should I leave one or all four of the stacks vented to create an air flow through the block.

Thanks in advance for all opinions

FindMe

Wow.... Well 1st of all, the pcv valve must be installed as to pull through the valve from the source of vacuum... in your case from the spacer. Make sure the valve closes when you blow in the direction of the nipple in your valve cover (can't blow through), and is open (can blow through) when blowing towards the spacer. A pcv valve size and flow rating is important because it can severely affect your fuel mixture, or the sealing of your motor (blows gaskets out & leaks oil) so selection is tricky. Also, you have to have a source of "filtered" air for the pcv to draw the vapors out of the crankcase, but open vents is not only overkill for a pcv system, but the air going into your motor is not filtered (or not keeping the big chunks out). K&N makes a great breather/filter for that purpose that goes in the valve cover.... Most boats, especially Offshore boats do not use a pcv valve because of the amount of pressure created by the mass of moving parts in the motor, but then it is crutial to make sure to get at least 160 degrees in the motor at all times to vaporize the condensation and blow it out the breather tubes you have. What you described will not work properly... it's either a correct pcv and an adequate breather for a source of air intake, or no pcv at all, replaced by breathers like you have. The LAST thing you want to do is seal off the motor by plugging the vent tubes or breathers, or the motor will suck the gaskets in, instead of blowing them out.... Are we havin fun yet?

MIKE H

Thanks for your reply.

Originally I asked if the valve could be installed so as to get rid of the smell that was coming from the engine while at idle or slow speeds. I had over heated the engine when I blew the main water feed off and had some blow by. The engine has since been rebuilt so the problem probably does not exist any more but I thought that I might as well install the PCV valve while the engine was out because the smell was not enjoyable to me. I don’t know if it bothered anyone else as they were always just thrilled to get out in my boat and go for an 80 mile per hour blast.

The engine was dynoed after the install of the valve but as with all controlled situations for dynoing it was tested at 160 degrees, the most I get in temp on the water is about 125 degrees so the engine is running quite fat. The plugs run almost black all the time, idle is very good though. I have not been able to re-jet yet. Ran out of season up here. The engine has an oil thermostat and I do get the oil temp up to about 180 degrees, so moisture has not been a problem. The Vent towers on the rocker covers all still have the sponge filter installed so the problem of filtering the chunks out is non existent as the PCV valve is into the sponge filter.

I feel that the boat ran faster before the last set up, so I was considering removing the valve and putting the carb back to the original set up.

bobby daniels

Hey just block the vents on the side the valve is on so that it pulls air in only through the other valve cover !!
Its not any big deal !! ,,,,block around the pcv so it can't pull air around it ,they do great ,great on boats they keep the condesation down and smell out and have been used for 20 plus years on boats for that reason ,,,great idea to have it !!!

Johno

In the process of re-building a HP 500 with Imco valve covers with no breathers on the valve covers. I have the PCV valve in the Intake manifold up to the bottom of the carb. Do I have vent my valve covers?
Thanks John

Dennis Moore

Don't make a big deal out of the PCV. It works of off intake manifold vacuum. As soon as the throttle is opened the manifold vacuum drops and the PCV becomes ineffective (it is spring loaded to close). It really only works at an idle on a marine engine (depending on the spring tension). The idle adjustment screws will recalibrate a carb after the PCV installation.

Venting the valve covers to the atmosphere will work but to be the most effective (at high speeds) the valve covers should be connected to the flame arrestor with hose. The flame arrestor vacuum (from the carb) will help pull some crankcase vapors from the valve covers at high speed.

Drag racers run a hose from the valve covers to the header collectors to pull vapors and pressure from the crankcase.

Sincerely
Dennis Moore

HOTROD2

Why not use an air pump to e-vac the presure from the crank case like we do on race cars ? You can return the air/gases to the air cleaner or vent thur hull and eliminate the smell from the engine compartment. We have an electric pump that draws 4-6 inches constant that works well up to approx. 600 hp.

bobby daniels

The pcv needs to be in a valve cover and the other cover needs a vent installed !!! Then it ca.n work

And air /vacum pump is great just expensive !!!!

turbo2256

On my engines I usually try to pull PCV from the intake manifold valley (most carb Chevy motors do this) and when possible install a valley pan. I then install one breather in each valve cover. I f the PCV is mounted to the rear of the manifold the breathers should be in the front of the valve covers. If the PCV valve is in the front the breathers should be at the rear. What is happening is that pressure/vacuum is building between bulkheads in the engine crank case. The pressure between bulkheads can very because oil, rods, crank cheeks block comunication. Thats why a lot of new engines have passages under the water jacket dedicated help to comunication. On our old school engines it is importent to locate a position for the PCV valve that will promote pulling the crankcase vapors from the crankcase. Some setups flow the path of least resistance. Say like a PCV in one valve cover and a breather in the other might not even pull a anything from the crankcase instead just from one valve cover to the other. One of my cars pulls PCV from a modified front cover were the fuel pump was mounted. A closed PCV system just has a tube running to the air filter instead of filters on the valve covers. That keeps emissions down a bit and keeps the outside of your engine cleaner.

BAD-HABIT

I belive there was a write up a few months back on just the same topic..I belive it was in F&PB Magazine. If I remember if done right it was actually good for most marine engines.....

Bad-Habit