327 Not Breathing Right?!?!

[Slick67]

Originally Posted by Hubscrub

i hear ya on cutting them but if it will make it "more right" its worth it to enjoy it.

Yep. I hate it, but it is saving the more important part........the engine!

Originally Posted by fleetsidelarry

slick67, what is under the yellow tape on the valve cover closest to the firewall?

it looks like a hole in the valve cover. or are these just temporary valve covers?

It is a pcv hole with a grommet in it that I just taped up. But these are just temporary till I get my breathers in today and installed.

[Slick67]

Here is something that doesn't happen too often, an actual update to a problem from the past. I did have to drill the vc's in the back but it was not bad at all. 5 holes total, 2 for the bolts and 3 for airflow on each. It seems that it took care of that problem, but I still show high oil pressure on my gauge in my cluster 75 at idle and 10+ while driving. I will have to buy an aftermarket gauge and test it on the front of the block to see what it is reading and compare it to the original in the cluster because the gauge may just be reading wrong. Although, I have gotten a little oil sepage at the front of the intake it may be from pcv in the valley. We will see!!!!

[67cheby]

where is your pcv ?

[Slick67]

Originally Posted by 67cheby

where is your pcv ?

What pcv? I am pulling from the oil filler cap which I have been told by several very savvy engine people that my setup is more than adequate for proper breathing. Still not feeling the warm fuzzies when I see a little oil at the front of the manifold. When I say a little oil, it is just a drop if that, but still it bugs me. Could that be from my previous issue and now the gasket is leaking just a tiny bit?!?!

[Slick67]

ttt

[jlsanborn]

I know this is little old and you've already installed valve cover vents but I thought I would share in case anyone else stumbles across this in their searches.

I also have an early 327 and will also run the script valve covers. Fortunately, I have the block mounted PCV connection. If I didn't, I would drill and tap the back of the intake manifold and fab a baffle to keep oil out. By simply installing vents you've eliminated the crankase pressure that would lead to oil leaks but you have not provided any fresh air circulation to combat the sludge issue. Ideally you'd want fresh air entering one side or one end of the engine with the exit being opposite. I would also suspect messy oil film/mist around your vents as they are the escape way for all the crankcase gasses.

EDIT- Just noticed that you do have a connection to vacuum, but no PCV? I'd think that would be drawing a lot of air (most probably right from the vented filler cap) giving you a lean condition?

Nice truck man!

[Slick67]

Originally Posted by jlsanborn

I know this is little old and you've already installed valve cover vents but I thought I would share in case anyone else stumbles across this in their searches.

I also have an early 327 and will also run the script valve covers. Fortunately, I have the block mounted PCV connection. If I didn't, I would drill and tap the back of the intake manifold and fab a baffle to keep oil out. By simply installing vents you've eliminated the crankase pressure that would lead to oil leaks but you have not provided any fresh air circulation to combat the sludge issue. Ideally you'd want fresh air entering one side or one end of the engine with the exit being opposite. I would also suspect messy oil film/mist around your vents as they are the escape way for all the crankcase gasses.

EDIT- Just noticed that you do have a connection to vacuum, but no PCV? I'd think that would be drawing a lot of air (most probably right from the vented filler cap) giving you a lean condition?

Nice truck man!

Thank you!!! This is the type of info that I was searching for. So I do have a lean issue but it is very slight. The oil looks good so that leads me to beleive that just a slight change in the routing of the vacuum lines may do the trick. Although the truck runs fine it does bog on quick acceleration, but not too bad.

I am going to look closely at all of my alternatives and pursue the best option.

[cleszkie]

If I'm not mistaken, the whole purpose of the PVC valve is to control when crankcase gases are introduced into the carb. At wide open throttle, or under loads, the manifold vacuum drops dramatically. Sometimes all the way to zero inches of Hg. This drop in vacuum prevents the PVC valve from openning, and thus the carb is only fed clean outside air during these times of heavy load. The PVC valve only opens during cruising speeds when the engine is producing enough vacuum (15 to 20 inches of Hg), and there is no big load. The engine can then consume the crankcase gasses without noticeable impact on performance or power.

By not having a PVC valve between your oil fill tube and the carb, you are feeding your carb crankcase gasses all the time, and this is affecting your wide open throttle and under load performance/power. The engine designers knew what they were doing when they introduced the one-way vacuum controlled PVC valve system. I suggest installing an in-line PVC valve between your oil filler tube and carb.

[Slick67]

Originally Posted by cleszkie

If I'm not mistaken, the whole purpose of the PVC valve is to control when crankcase gases are introduced into the carb. At wide open throttle, or under loads, the manifold vacuum drops dramatically. Sometimes all the way to zero inches of Hg. This drop in vacuum prevents the PVC valve from openning, and thus the carb is only fed clean outside air during these times of heavy load. The PVC valve only opens during cruising speeds when the engine is producing enough vacuum (15 to 20 inches of Hg), and there is no big load. The engine can then consume the crankcase gasses without noticeable impact on performance or power.

By not having a PVC valve between your oil fill tube and the carb, you are feeding your carb crankcase gasses all the time, and this is affecting your wide open throttle and under load performance/power. The engine designers knew what they were doing when they introduced the one-way vacuum controlled PVC valve system. I suggest installing an in-line PVC valve between your oil filler tube and carb.

That is exactly what I was thinking. I appreciate you explaining this in detail and taking the time to explain other issues. You guys are awesome!!!

[jlsanborn]

The PCV (positive crankcase ventilation) valve is normally open at zero manifold vacuum (engine off). At idle you have high manifold vacuum that nearly closes the valve. Combustion chamber blow-by is low at idle, so you don't need that much flow anyways. At idle you will have minimal "un-metered" PCV air entering the intake. Under load, vacuum drops and allows the valve to open. Blow-by increases under load but now there's an open path to the intake. At higher revs the amount of "un-metered" PCV flow is minimal in comparison to the "metered" air.

Without a PCV you basically have a big vacuum leak. At idle or low RPM that vacuum leak is substantial in comparison to the "metered" air and will cause the lean bog or hesitation when you open the throttle. Once the revs come up, that vacuum leak becomes small in comparison to metered flow.

The filler tube with the hose barb on the side and the non-vented cap are available on E-Bay. I'd check them out. I bet a PCV cures your lag and you'll rest easy knowing there's a clean breeze keeping that motor cleared out!

My sketch is not real accurate. I'll re-draw that tomorrow for clarity.

[jlsanborn]

Originally Posted by Slick67

That is exactly what I was thinking. I appreciate you explaining this in detail and taking the time to explain other issues. You guys are awesome!!!

See, I haven't done mine yet so I'm hoping YOU get it all sorted out and I'll just copy you . Just like the two-tone scheme on Cloud 9's grille that I'm going to copy!

[northern 85]

Great info guys!

[TBONE1964]

Maybe I can help a little.

PCV as in Crankcase Ventalation. As it imply's, vents the crankcase. Anything that rotates in an inclosed space surronded by oil builds pressure. This pressure needs a place to go or it will blow out seals and gaskets. That is the primary function of a PCV valve and the vacumn helps it by sucking it out of the crankcase and into the intake ports (in most cases) so it will burn off any gases that are in the oil. If you look at a rear end housing or any transmission, they are vented to relieve pressure build up and prevent seals from failing and blowing out.

Crankcase pressure and oil pressure have nothing at all to do with each other. The reason that PCV's were invented is because the old style down draft tubes would allow oil to leak and not only make a mess on the ground but had the potential to start fires.

[jlsanborn]

The PCV was invented to reduce emissions. All crankcases and gear boxes are are vented. Not just blow-by but thermal expansion also requires it. The road draft tube was invented to "draw" fresh air through the crankcase to combat the condensation/acid/sludge thing. The end of that tube was at a low-pressure area under the car (when it was at speed) and was connected to the back of the block. This created a pressure differential between the end of the tube and the vented filler cap, which in turn caused an airflow from the vented (somewhat filtered or screened) filler cap, through the crankcase and out the road draft. Even though there's a baffle in the lifter valley, the car spewed unburnt fuel and yucky oil mist stuff. The PCV enabled that air flow to be directed back into the combustion chamber where it could be fired again. The beauty is that the PCV is "load sensing" and will nearly close as not to lean out your motor at idle/low speed but will "pass gas" almost un-noticed while the motor is swallowing lots of air.

If you're not all that worried about the planet or oil spots on the driveway then the road draft would be better than nothing. Who want's nasty-gas or oil in their combustion chambers anyway? I think the PCV system is cleanest and can be accounted for on the power-mode calibration of the carb/fuel map.

[jlsanborn]

Here's a better illustration of the PCV valve. The blue flow arrows show flow direction towards the intake from the crankcase. You can see how it's nearly closed at idle (high vacuum) and won't cause a lean condition.

[Slick67]

Originally Posted by jlsanborn

See, I haven't done mine yet so I'm hoping YOU get it all sorted out and I'll just copy you . Just like the two-tone scheme on Cloud 9's grille that I'm going to copy!

Hey Everyone! This is some really great info for everyone to use. I have learned alot just from reading and re-reading these last few posts. This weekend was full so I was not able to run the in-line PCV valve, but I will do it this week or coming weekend and let everyone know if there was a noticeable difference.
Check out Mike's Cloud 9 valve covers, he waited to make sure it worked for me and then did the vents at the back of his.....so I am a guinea pig and proud of it!!! If anything that I did helped anyone out I am proud of that!!!

[jlsanborn]

Man you've got a sweet truck and details like this would go un-noticed by most people. What you have now is an attempt at crankcase ventilation but is causing you a big vacuum leak at low-speed. You have three options....

1) Pull that line between your filler cap and carb and plug both ends. Vacuum leak is gone and you've got three crankcase vents (both valve covers and the filler cap). You won't blow gaskets but all three vents are going to be greazzy and you're not ventilating (fresh air) your crankcase.

2) Change to a non-vented cap and a filler neck with the hose barb and install the inline PCV. This will kill the low-speed vacuum leak and draw fresh air from the vents you installed in the valve covers.

3) This is what I'd do.... Fix or replace the script valve covers (no leaky holes like they oughtta be). Drill/tap/baffle the intake manifold (if you're sure your block dosen't have those provisions already) and install a PCV valve between there and one of the the big vacuum ports on your carb. Get the non-vented filler cap and the filler tube with the hose barb so you can run a line from there to the air filter housing. This will get you the best of all worlds! - no holes script valve covers, fresh air cross-ventilated crankcase, finely filtered ventilation air (your air filter as compared to the crappy screen/mesh in you valve cover vents or vented filler cap) no oil drippy vents or draft tubes = CLEAN. Who dosen't like clean?