PCV?

[68chargerboy]

Hi,  i was wondering if i need to use the pcv off of my valve cover to my carb.  ive heard i dont need to and ive hear i should.  what do you guys think.  thanks,  Zach

[8WHEELER]

Run it to the carb, a street car needs it. If it was a race car then there are other options  .

Dan

[dodge freak]

I have been using mine for the last 3 years on my rebuilt engine but did not have one before then. I too have heared that the motors "need" them but they only been around for around 40 years. In the 50's there was no such thing, the engines had a draft tube. Would like to seen more info on that but it was so long ago . Does anybody use a electric vacuum pump? I know there something for headers but hear its only for open headers.

[Silver R/T]

would be possible to just run air breathers?

[71charger_fan]

Road draft (or draught depending on manufacturer's literature) tubes were very simple yet effective devices. At road speeds they performed the function of today's PCV. On my '59 Coronet it came out of a breather fitting on the back of the passenger side valve cover and went down the back of the engine to within a few inches of the road. It used the property of pressure and velocity being inversely proportional. As your vehicle gained speed the velocity of air passing over the end of the tube increased thereby causing the air pressure at that same location to drop and, essentially, sucking the vapors out of the engine. You can see the same exact principle at work on drag cars that have their breathers plumbed into the headers. If you were going to sit in traffic the road draft tube was a smelly pain in the a$$. For a modern street car, the PCV is a much better answer. The PCV was a more environmentally friendly way to accomplish what the draft tube was doing.

[grouseman]

Yes, run PCV.  You don't want to see what the inside of an engine looks like without one. 

[68chargerboy]

would i be able to just run brether caps off of my valve covers like Silver R/tT said or not?   Thanks

[dodge freak]

Sure you can run it that way but the pcv may keep the motor cleaner inside, unless you drive full throttle most of the time, which I doubt, pcv only works when vacuum is high. Thats why drag racers don't have them, Moroso makes a pulley vacuum pump, looks a little like a power steering pump that sucks the engine vapors out, the faster  the engine spins the more vacuum, not cheap $ 400 or so.

[TylerCharger69]

PCV.....meaning...positive crankcase ventilation.   Yes...use it!!!    Some folks use a pcv valve on BOTH valve covers.   I would definately recommend one though.....for a street car or daily driver that is....

[68chargerboy]

ok thanks now that i have heard all of this i will definitly use my pcv on my car.  i am just trying to find out little tips to add hp to my 383 so i can smoke some ricers.  i was also wondering if i should use the vaccum advance on my distribter or not. thanks


           P.S. if anyone has some ideas to get my car moving faster with upgrades please tell me, thanks alot.

                                   Zach

[grouseman]

  i was also wondering if i should use the vaccum advance on my distribter or not.

Gawd YES use the vac advance!  Otherwise you're wasting money and losing part-throttle response, among other things. 

[dodge freak]

If you have light springs in the dist. so the advance comes in by 2500 or so using the vacuum advance could give the motor to much timing, however if using the stock heavy springs so the advance is not all the way in till around 4000 then the vacuum advance could be useful. I have 3.91 gears in back and the engine does not ping even in third gear taking off from a stop, I have a manual valve body in my "automatic" trans. If I use the vacuum I can feel it firing too soon, when in park you can see the engine shake and hear it slow down. If your motor is mostly stock and you have 2.73-3.23 gears you most likely will not be able to use the light weight springs in the dist. and the vacuum advance would most likely help out.

[Chryco Psycho]

  i was also wondering if i should use the vaccum advance on my distribter or not.

Gawd YES use the vac advance!  Otherwise you're wasting money and losing part-throttle response, among other things. 

I disagree , by not using the vacuum you can run more initial timing & a shorter curve so it wil not over advance at high rpm  & increase both power & milage under virtually all conditions

[grouseman]

Each of initial, mechanical, and advance timing plays a crucial role in an engine's performance.  I'm guessing that 68chargerboy has a basically stock engine and drivetrain, not a 1/4 mile trailer car.  He needs to coordinate all three types of timing for maximum performance; you can't just dial in more/less initial/mechanical without any vac advance and have it run it's best.  You can adjust each one for maximum performance.  Too much initial will be hard starting.  Too little will give you no low-end response.  Coordinate your max. mechanical advance with your vacuum advance to eliminate pinging.  Remember that all Mopar vac. cannisters are adjustable to sensitivity to vacuum.  There are different mechanical advance plates for amount and type of curve, and the springs can alter the rate.  The number of degrees advance is stamped on each plate (but multiply by 2 to get crank degrees). 

At part throttle/high vacuum conditions, fuel burns more slowly so it needs more advance timing.  It's up to you to adjust it to keep it away from 'rattle', and to set your mechanical for low vacuum WOT conditions.  To do this properly, you need either a dial-back timing light or a degreed balancer, tachometer, and a vacuum gauge.  Graph out the timing curves vs RPM and also vs Vacuum, and you'll get a sense of where things need to be adjusted. 

[mikepmcs]

  
Love to see a video of all that being done. 

I got the dial up and all and have mine tuned pretty good.  I have the vac advance plugged ...only ... to see if there is a difference in power since i advanced it to 36*.  I ran it without vac advance but haven't plugged it up to run it with yet due to rainy days here in maine. I just want to see if i can feel a difference.  If so i'll try and dial the vac advance in.
I still think my carb is too small though, 600 eddy perf/eddy perf mani/484 MP cam.l
v/r
Mike

[firefighter3931]

I don't run one myself. As long as the crank case is vented then you won't have any problems. The pcv valve is a pollution device and takes oil vapour from the crank case and sends it back ito the chamber to be burnt/consumed. This dilutes the incoming intake charge and will impact on peak performance. I don't want oil in my combustion chamber...just air, fuel and spark 

A breather on each valvecover is sufficient should you decide to delete the pcv valve.

Ron

[mikepmcs]

Thank you Firefighter, you answered a question I had on that.  I pulled my PCV one day and was like hey, isn't that oil gonna get back in my chamber.  I'm gettin an air breather today!! 

[grouseman]

I don't run one myself. As long as the crank case is vented then you won't have any problems. The pcv valve is a pollution device and takes oil vapour from the crank case and sends it back ito the chamber to be burnt/consumed. This dilutes the incoming intake charge and will impact on peak performance. I don't want oil in my combustion chamber...just air, fuel and spark 

A breather on each valvecover is sufficient should you decide to delete the pcv valve.

Ron

The air drawn in through the PCV valve is part of total carb air that is metered against fuel during idle and high vacuum conditions; it's not diluting anything or harming performance.  Fumes are sucked into the PCV due to the port being below the throttle plates and getting a high vacuum signal.  The amount of oil vapour going into your combustion chamber is nothing to worry about.  At WOT, there won't be a high vacuum condition below the throttle plates, so the PCV is 'not in the loop' so to speak.  Besides capturing oil and combustion fumes, it also puts a slight vacuum in the crankcase, which also helps some other stuff, I forget what now (ring seal?).  There is no good reason or need to disconnect it on a street car.  A race engine is not a street engine, and just because a race engine doesn't have something is not enough reason to delete it from a street engine thinking you're gaining some performance. 

Oh, and my apologies for hijacking an ignition topic onto a  PCV thread. 

[firefighter3931]

I don't run one myself. As long as the crank case is vented then you won't have any problems. The pcv valve is a pollution device and takes oil vapour from the crank case and sends it back ito the chamber to be burnt/consumed. This dilutes the incoming intake charge and will impact on peak performance. I don't want oil in my combustion chamber...just air, fuel and spark 

A breather on each valvecover is sufficient should you decide to delete the pcv valve.

Ron

The air drawn in through the PCV valve is part of total carb air that is metered against fuel during idle and high vacuum conditions; it's not diluting anything or harming performance.  Fumes are sucked into the PCV due to the port being below the throttle plates and getting a high vacuum signal.  The amount of oil vapour going into your combustion chamber is nothing to worry about.  At WOT, there won't be a high vacuum condition below the throttle plates, so the PCV is 'not in the loop' so to speak.  Besides capturing oil and combustion fumes, it also puts a slight vacuum in the crankcase, which also helps some other stuff, I forget what now (ring seal?).  There is no good reason or need to disconnect it on a street car.  A race engine is not a street engine, and just because a race engine doesn't have something is not enough reason to delete it from a street engine thinking you're gaining some performance. 

Oh, and my apologies for hijacking an ignition topic onto a  PCV thread. 

Well,as they say everyone has an opinion.    I'll disagree on the oil vapour issue because i've seen how much can make it's way into the combustion chamber. If you're curious to find out; try running a clear fuel filter inline between the pcv valve and the vacuum source and see how much oil accumulates. 

Or just run tubes from your breathers into a remote (vented) catch can and see how much oil you have in there. 

Back in the day, breathers simply drained towards the ground via hoses.....worked fine back then.


It all boils down to personal preferance, inmo. Do what makes you feel comfortable. I prefer not to have oil vapour polluting the cumbustion process in my engines. On a mild or stock engine that was primarily for cruising, i would probably consider running one where performance wasn't the main focus, but for anything that will be stepped on hard....no pcv for me. 


Ron

[dodge freak]

I used to run 3/4 heater hoses on both sides down to the ground before I had my engine rebuilt, It work great. Now I don't have much blow by so I run one but sometimes wonder if it be better off without one. If I was young or was driving it flat out on the freeway everyday it be gone.

This gas is so clean now maybe some oil in the combustion chamber might be good. Replaces the lead that used to in it. Spark plugs might get dirty but if you have a strong spark should not be a problem.Thats why I love my MSD 7 al box and coil, wasn't cheap but was well worth it.

The biggest problem with a pcv is that when the engine is working hard-low vacuum the vapors have no where to go-if its only for a few seconds so what but if you have a lead foot it matters.

If your cam has low vacuum at idle I would get rid of it, just a vacuum leak you don't need thats why I still have mine, if I ever got a big cam for it I would throw it away.

[grouseman]

If you're getting THAT much oil going through your system, you may have other issues.    The amount of oil vapour, relative to the volume of air and fuel going through an engine in good condition, is tiny.  How much oil does your engine go through between fill-ups?  My Olds uses about a litre between oil changes (3,000-5,000 km).  And most of that is from a drip around the front crank seal.  But remember, I'm talking a street engine here, not a race engine with low-tension rings and lots of clearance and blow-by.  

Maybe you don't recall what the roads used to be like before PCV became almost ubiquitous; LOTS of oil coating the center of the lane, and I'm sure that was the cause of many accidents as tires when through that greasey section during emergency braking.  PCV is a good thing that doesn't hurt performance or foul spark plugs.  

But, as always, this opinion is worth what you paid for it!  

[mikepmcs]

I got 2 breathers today and i'm gonna check it out( if the rain ever friggin' stops ) , what the heck cost me 12 bucks for 2.
thanks for all the responses though, I learn so much from this place, it's priceless.

oh and I don't have a vac monster for a cam either.
v/r
Mike

[68chargerboy]

i have changed my mind to my original thought.  after hearing about the oil vapors in the combustion chamber i decided to put on two breathers.  thanks alot for the info.

                      Zach

[dodge freak]

What is so bad about oil? I even add a little to my gas, helps keep the valves from sticking and lubes the walls , I would rather have the lead back in the gas but thats gone so its oil for me.

I use trans oil or 2 stroke engine oil just a few oz to a tank of gas, all gas is is a lighter grade of oil gas comes from oil and this gas today has less "oil" in it than it used to part of this clean air stuff.

[firefighter3931]

What is so bad about oil?

The crankcase has dirty oil in it, not clean "virgin" oil. Agreed, a little (clean) oil wouldn't hurt but a lot will foul plugs, create a lean condition and affect performance. The crankcase doesn't care how it's vented....just as long as it is vented. 

Where the oil vapour ends up is the difference between a pcv valve and a breather that just releases it into the atmosphere. What's good for the environment isn't necessarily good for your engine. The pcv valve is nothing more than a pollution device designed to recycle vapour back into the engine to be consumed rather than directly released.

I'm not advocating that everyone go and rip out their pcv valves, just merely explaining the pros & cons of running one. On a daily driver ; no problemo.....on a weekend warrior/performance build ; no way. 


Ron