PCV Bypass

[Logical1]

Hey, Did several searches around this thread and the others but didn't find a clear answer. I'm putting in a oil catch can and then a filtered vent on it to the atmosphere for the crankcase output. Not sure what to do about the inlet 1 way PCV valve on my intake.. it draws air now and there isnt much diff when i plug it with my finger but was curious about advantages/disadvantages of blocking it or throwing a filter on it and just letting it suck in clean air... I have the L20b with Dual Su's at the moment and most likely not going to change that soon for cost reasons...

[72240z]

Letting it suck clean air would be a bad thing, better to plug it.... and even better to just use it the way its designed.

 

I personally would not vent the catch can to the atmosphere and instead run it to the pcv. You maintain the pcv's function and you don't suck in any oil, win, win.

Edited August 6, 2009 by 72240z

[hang_510]

and just letting it suck in clean air...

 

Positive Crankcase Ventilation, it doesnt suck, it blows :lol:

 

X2 on the can vent back to the PCV

[datzenmike]

Hey, Did several searches around this thread and the others but didn't find a clear answer. I'm putting in a oil catch can and then a filtered vent on it to the atmosphere for the crankcase output. Not sure what to do about the inlet 1 way PCV valve on my intake.. it draws air now and there isnt much diff when i plug it with my finger but was curious about advantages/disadvantages of blocking it or throwing a filter on it and just letting it suck in clean air... I have the L20b with Dual Su's at the moment and most likely not going to change that soon for cost reasons...

 

There is no reason for removing or plugging the PCV system. None! The valve cover end should be connected to the air filter so that only filtered clean air enters the motor. A small air filter on the end is ok. I believe race cars have to have this end connected to a catch can to contain oil in the event of a blown motor but for the street this is a ridiculous waste of time. The pipe and hose exiting the driver's side of the block should remain connected to the PCV valve on the intake.

 

Here's why:

All engines produce burned and unburned gasses, water vapor and oil fumes that push past the rings and enter the inside of the crankcase. If left they will condense when the motor cools and collect in the oil pan. This reduces the life of the oil and dilutes it reducing it's effectiveness as a lubricant. Unburnt gas will collect as a white paste in the bottom of the oil pan. Moisture will cause rust.

 

The PCV system uses a small amount of intake vacuum to draw these fumes out of the crankcase and burn them in the motor. In normal operation as the fumes are drawn out of the crankcase fresh air is pulled in through the vent in the valve cover and air filter to replace it. Under hard throttle there may be too much blow-by and the extra volume will reverse out the valve cover vent and be drawn into the carburetor. If you have a small air filter on the valve cover hose you may notice a smell from this extra blow-by so having it connected to the stock air filter is best.

 

The PCV system has ABSOLUTELY NO effect on performance and has everything to do with keeping the inside of your motor clean and rust free, and your oil clean and doing it's job.

[Charlie69]

Thank you Mike and the other Ratsoners' for clearing this matter up. I for one thought it is peter to use the pcv valve than to filter the hose. In my opinion the filtered hose on a street driven vehicle looks like the owner did not know where the hose went so he stuck a filter on it or even worse yet a bolt in the hose.

[Logical1]

Awesome post Mike, Truly informative! I pulled the filter off and ran it back to the Intake and all is happy (not that it wasn't..... YET) I picked up one of the really nice Catch cans that has the stainless mesh maze inside to re-condense oil fumes and so I'm sure the gasses heading back into the intake are nice and clean :) On a purely academic note: I'm curious about air intake there... If cold air intakes, Ram air ect, ect.. increase the available o2 that is passed into the combustion chamber in there own various ways and the pcv system is pulling burnt gasses, oil & water vapor back into the combustion chamber would that not be including useless/harmfull gasses? if the small amount of o2 increase from a cold air intake increases the power of the combustion, then if the engine were only pulling fresh cold air in be maximum effective burn? and thinking about the pcv system 'cleaning' the crankcase of those harmful vapors and a breather line is not enough. Could you not hook up a small 12v vacuum pump on the outlet of the catch can to make sure the proper amount of suction was provided to rid the case of those vapors? I understand this is all abit crazy but I my mind really works in strange ways ;) and like I said purely academic!

[72240z]

We're talking minuscule amounts. I think your delving into this negligible subject too far.

[HRH]

The catch can can be vented just fine, but if the PCV system is operating correctly, it should still suck all the gases back into the manifold to be burned. I have an open air breather at the valve cover, and the lower block vent goes to the pcv valve.

[south of reno]

So, bottom line...what do you think of a catch can ridiculous or not is it a good thing to have?

Cause i got one lying around and was wondering if it's worth the effort installing.:huh:

[DanielC]

DatsunMike has it right about the PCV system. One more advantage about it. It creates a slight vacuum in the crankcase, and this helps to reduce oil leaks.

[datzenmike]

So, bottom line...what do you think of a catch can ridiculous or not is it a good thing to have?

Cause i got one lying around and was wondering if it's worth the effort installing.:huh:

 

If your engine is a good runner then oil spray out the vent is negligible. Oil spray is pushed out the valve cover vent by excessive blow-by. If you have this problem then a catch can will keep that oil from coating the inside of the air filter or dribbling all over the motor if you choose to use the funny little blue air filter. Catch cans were designed for, and in some cases required, for racing where ultra high RPMs are common with lots of oil mist created. They are required as a back up to catch oil as a result of a blown engine and to keep it off the race course.

 

 

Bottom line... If you need one, use one. If you don't need one you can use it or not, but it's there for show if you do, sort of like a spoiler or hood pins.

[south of reno]

I see, ok then, sense i have one no harm in putting it in.

I'll get that poser look lol

[Spades]

Thank you Mike and the other Ratsoners' for clearing this matter up. I for one thought it is peter to use the pcv valve than to filter the hose. In my opinion the filtered hose on a street driven vehicle looks like the owner did not know where the hose went so he stuck a filter on it or even worse yet a bolt in the hose.

 

I have a filter on the end of my valve cover vent...because there is so little clearance between my NAPS Z24 and my hood, a hose is out of the question. It really doesn't matter, it is like Mike said, as long as there is a filter on it, the worst you can get is some smell(which I don't have). The rest of the PCV system NEEDS to be there on a street driven car...period.

[yellowdatsun]

Why would you want a catch can on a normal L-20 with SU's???? Answer yourself this first. There's no reason for it. in 95% of all cases, people put them on for the bling factor, "Ohhhh, shiny aluminum can". In my opinion, it's just un-neccesary extra crap in the engine bay. A hot turbo motor would be a different story. As Datzen pointed out, a properly functioning PCV system is actually a GOOD thing, and does NOT hamper performance.