I've read a bit about the PCV mod here and other places regarding the LS1 and have some questions. The PCV mod appears to both restrict air/oil flow through the PCV system and trap some small amount oil before it can re-enter the throttle body. This has the reported benefits of:

(1) Reduced oil consumption.
(2) Reduced fouling of the intake, plugs, etc.
(3) Reduced knock/ping due to oil not being burned in the intake.

Before I think about doing this myself, I do have some questions that I don't believe have been answered here or elsewhere that I've found. My questions relate directly to the benefits above:

(1) Reduced oil consumption.
I've read some reports about oil consumption going from a quart every 2000 miles to almost nothing. This would imply that a quart of oil was being burned every 2000 miles because it was entering the throttle body through the PCV system and being burned off. If oil consumption is reduced (in cases where ring blowby is a problem), where is that quart now? The reports seem to indicate only a teaspoon or so of oil in the filters after the mod is made so to me, this means that a quart of oil that *was* being taken up and burned by the PCV system is now just creating a quart of [potential] sludge in your crankcase. In other words, if you had a quart of oil being blown by the rings and consumed by combustion before, that quart is now "recycled" into your engine oil. Is this something you really want? Is this really better than burning it?

(2) Reduced fouling of the intake/plugs
This would be the only reason I am considering this mod. My 99 doesn't burn much (if any) oil so the problem is not a big one for me, but I can't argue with keeping the intake clean.

(3) Reduced knock/ping
Ok. Let's assume that your car burned 1 quart of oil per 2000 miles before the mod and now burns none except maybe under hard driving. If you only got 20 miles per gallon, you are talking about burning 1 quart of oil with about 100 gallons of gasoline. That's 1/100 (.01) quarts per gallon, or the equivalent of taking a gallon of gas and dumping just under 2 teaspoons of oil into that gallon of gas (a gallon is about 768 teaspoons). Is that enough to cause knock? Maybe. I doubt it. But maybe. The only problem is, I think adding oil to gasoline actually *increases* it's octane rating because it makes the gas burn more uniformly/slowly. Also, at full throttle, the PCV system is only pulling in a very small fraction of what it pulls in at part throttle because the throttle plates are open and very little vacuum exists there... so I'm assuming the pink/knock we are talking about is part throttle knock? For those getting knock/ping that goes away with the mod and comes back without it, is it possible that the knock goes away as a side effect of the PCV mod and not the fact that your engine is physically burning a small amount of oil? Basically, this mod is simply blocking the flow of oil back to the intake. It's obviously not just trapping it somewhere else otherwise you'd have a quart of oil to collect from somewhere after 2000 miles instead of only a teaspoon full or so. What this means to me is that you are simply blocking/restricting the flow of the PCV system so that it is no longer sucking as much air into the intake. Could it be that by doing this, your car simply doesn't pink/knock as much any more because the MAF is now metering a greater percentage of the intake air? With a free flowing PCV system, you've got some percentage of air that is being fed back to the intake, upstream of the MAF that measures air. By blocking that, you get more metered air passing the MAF and will get a little richer mixture as a result. THAT could be the reason that the pink/knock disappears! If so, you could probably also get rid of your ping by just installing a MAFT and richening your mixture a tad.

Thoughts? Comments?

Mike

 

The pinging is probably due to the carbon deposits left on the piston crowns as a result of the oil being burnt. These deposits increase the compression ratio and causes pre-ignition. Thats why the GM top cylinder cleaning solvent fixes (maybe temporarily) pinging. The oil consumption issue is probably a combination of poor ring seating and/or incorrect factory installation, and PCV oil pull-thru.

 

I've had that PVC mod in for about two months and in the end after a bunch of drag race runs, lots of street miles a total of ONE DROP of oil in one of the filters and nothing in that catch can.
So for me the PVC had zero issue with my knock and my engine is not only clean but also does not burn any oils.
I yanked the two filters out and inlarged that funneled coupling to increase venting.

My pings are almost only within the 2,000 RPM range and about zero when in WOT. In below 80 degrees weather knock is gone.

I also use 1 can of 104+ octane booster for every three tanks of gas and that stuff assures pistons are kept clean.

John

 

Your pinging is from not enough Octane.

I add 2.5 gallons of high Octane 109 unleaded (blue) with every fill-up. This brings my Octane up to 95.

This is a sure fix for pinging or detonation.

I keep 2 five gallon tanks at home and every fourth fill-up I have the 2 five gallon tanks replenished. It's not that expensive and not that much of a hassle to eliminate detonation. Make sure it's blue and not purple fuel. Purple fuel is leaded and you never ever want to use leaded.

Zona. :seeya

 

My main concern about the mod is this:

The original creator of the mod claimed that his car burned about a quart of oil in 2000 miles before the mod and almost none after the mod. This means that 1 quart of oil fumes were being evacuated from the crankcase prior to the mod. If after the mod is done, you only get a teaspoon or so out of the filters and your car isn't burning any oil, that means that the quart of oil fumes (minus a teaspoon or two) is now staying in the crankcase rather than being evacuated. You've done nothing to change the amount of blowby fumes in the crankcase, so you'd have to assume that if the same amount of air was being drawn from the crankcase, you'd "lose" the same amount of oil (1 quart) whether it was burned or existed in one of the filters. Bottom line is, as far as I can tell, all this mod amounts to is putting a (big) restriction in your PCV system so that it no longer sucks nearly as much air.

Is this really what you want to do to your engine?

Mike

 

If I understand you correctly, your concern is basically the potential impact of the reduced PCV airflow. This has been discussed before, and the only potential negative that I've heard is that it will cause the oil to become "dirty" sooner. In order to look into this, I took an oil sample at my last change. I got the results back today, but I'll start another thread to post the results.

 

As you reduce the flow, the vapor residence time increases resulting in greater absorption by the oil. Reduced flow also hampers contaminant "burn off" that occurs at elevated oil temperatures in the presence of adequate ventilation.

It is important to recognize that there is a proportional relationship between PCV flow and oil contamination. You cannot simply say that if there is flow, it is OK. I would be very interested to install a flow meter in series with/without the various mods.

I second mchaney's comments about the octane vs. carbon deposition theory.

I appreciate the spirit behind the SMH modification, but Fuel filters are grossly inappropriate for this application. The media and physical configuration do not lend themselves to effective demisting, flow, or drainage. A thick coalescing media should be used in an orientation where the resulting liquid is captured away from the bulk of the flow and without restricting the media. Look at a good quality air compressor demister for some good design ideas (but I think they would be too restrictive for this application).

So I am not providing criticism without suggestion:

I guess we have to define our design goals - do we wish to remove the majority of the vapor, or just the droplets and liquid? I am using a sealed Jaz can with no media to capture the liquid flow in the line as well as the larger droplets. It meets my goals by capturing a significant volume of oil with little or no restriction.

If you want to capture the majority of the vapor as well, you have to go a step further. A free-flowing media is required in the catch can to demist and coalesce. Media could be squeezed into the Jaz can, but the inlet and outlet are not well positioned for greatest media vapor exposure (flow across the top rather than forcing it through the majority of the volume). The same goes for the artful Greddy can. Ideally, the inlet needs to be near the bottom, but above the liquid level. The exit needs to be at the top. This forces flow across most of the media while benefiting from gravity to pull resulting liquid away from the outlet.

It may be possible to fashion a little tube on the inside of either can to force the flow inlet to the bottom of the filter, but the challenge is to do so without reducing the tube diameter. I guess you could relocate the inlet as an alternative.

While I am sure that we can find a commercial coalescing media that would be ideal, lightly packed stainless or plastic "scrubbie pads" could be used. (no soap coating of course)

As an alternative to modifying either of the catch cans and adding coalescing media, experimenters (or the budget minded) may want to experiment with fabrication from PVC pipe. Try a 3" x 8" PVC pipe, lightly packed with media and capped at both ends. Insert a barb at the top for the outlet and a barb about 2" from the bottom for the inlet. A petcock in the bottom can be used for drainage. You probably will not find one in my engine compartment, but I think this will give very good results for the experimenter or budget minded. And you don't even have to name it after me.

OK Jaz and Greddy, can you build us something appropriate for this application? I think I will email this thread to them and hope they realize how many of use are seeking a solution like this.




[Modified by C5 Tweaker, 3:13 PM 9/8/2001]