PMS Question - Is a VC breather better than a line back to the intake?

So check this out. I just got done building my 325 stroker and I have the ford racing tall valev covers on it right now. I hooked up the tube from the throttle body and have it going into the valve cover via a grommet. When my car is running and I pull the dipstick out it creats a huge vacuum type suction sound, very very loud! That is scarey I think I need to vent the crankcase So I am goung to try and plug the tube now and run a breather and see if this changes things.

$uperstang said:

So check this out. I just got done building my 325 stroker and I have the ford racing tall valev covers on it right now. I hooked up the tube from the throttle body and have it going into the valve cover via a grommet. When my car is running and I pull the dipstick out it creats a huge vacuum type suction sound, very very loud! That is scarey I think I need to vent the crankcase So I am goung to try and plug the tube now and run a breather and see if this changes things.

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Do you still have the pcv in place? Most likely that is where the air is being pulled out of the crankcase from.

vristang, FYI I read sigs.

blackcloud50 said:

My thought on this issue are as follows:
With pcv still connected and using a breather, any unmetered air that gets into the combustion chamber and causes a "leaner" condition would be quickly addressed by the ECM's ability to adjust and correct a/f ratio based on feedback from the O2 sensors (O2s would see a lean condition). Otherwise no since in having O2s. Now if one is using a tuning device, a/f ratio can be adjusted to compensate for what would have been a very temporary leaner condition caused by using a breather with pcv still connected right from the start.

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Although this maybe true in closed loop, it doesn't apply to open loop (usually WOT) because at that point the computer does not look to the 02's for information.

69clark said:

Although this maybe true in closed loop, it doesn't apply to open loop (usually WOT) because at that point the computer does not look to the 02's for information.

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That is correct. But with regards to the "unmetered" air scenario making for a lean condition when using the stock pcv setup and breather (when in vacuum), WOT wouldn't be an issue because at that point the pcv valve is shut, therefore can no longer pull in any unmetered air from the valve cover breather.

So basically my understanding:

1. Using the pcv valve setup and open breather may let in some unmetered air but not enough to affect a/f ratio where the ecm can't compensate by adding more fuel once it gets feedback from the O2s for a lean condition....unless one has already gone past the limits of the ecm's adaptive capabilities. Getting tuned via a chip, piggyback to stock ecm, or standalone fuel management unit will take care of issues where the stock ecm has reached its limits.

2. WOT and unmetered air entering the combustion chamber is not a concern because pcv at this point is non-functional, therefore no unmetered air can be drawn in from it.

Running the pcv with breather and concerns of unmetered air entering the combustion chamber, I think, has been hyped up to be much more of a problem than it actually is.

Just a quick thought here

Some say CL conditions will, or may effect OL conditions

soooooooooooooo

Things here may not be as one thinks

This is something that takes some time or a long term thing btw

I'm not sure myself

I try to not set myself up for things such as this and that way I hope to avoid potential probs.

Grady

blackcloud50 said:

2. WOT and unmetered air entering the combustion chamber is not a concern because pcv at this point is non-functional, therefore no unmetered air can be drawn in from it.
.

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Not exactly true.
You are thinking that the pcv works on intake plenum vac, but in reality it is the pressure differential between the intake vac and the crankcase pressure.
At wot there is very little vac signal (if any at all), but wot will create more crankcase pressure, which will unseat the pcv valve (this will be especially true at higher rpms).

My point of view is this.
Maybe the computer can compensate for an open breather, but why would you force the computer to guess at what is really happening in the motor.

The whole reason I purchased a tweecer is so that I can tell the computer that I no longer have 24lb injectors, and a stock maf/tb. The computer will be able to do its job better, if you feed it better data.

jason