[DMCForum] Questions for Martin....
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[DMCForum] Questions for Martin....



Question #2: Why does engine moan internally as soon as breather tube
>from air filter housing plugged? If passive shouldn't care.

It's not passive, see below. You're pressure relieving the valve 
cover/timing cover through the crankseal. Thats the sound you hear.

>If you block the breather pipe for example, the exhaust gases 
blowing into the crank case will have nowhere to go and you'll start 
blowing seals all over the place. It's not a vacuum/pressure seal, 
it's an oil seal!<<

Mate, yer doing me proud. See the post I made on the other list..

>Here's a guess. The dipstick tube goes quite far down, as already 
stated, the crank case will be under a slight pressure at all times, 
if you leave the dipstick out, you might find you get oil and not 
fumes pushed out the top. THAT's a guess.<

The crankcase needs to be ventilated, we all know that. But where 
would the vacuum come from in a normal blowby enviornment? Most cars 
has warning about dipstick sealing, it's for the PCV system.

>Question #8: Has anyone ever run their PRV with valve covers off?<

Yes, I have.

The function of the hose coming from the air cleaner to the oil 
beather is dilution air for burning the gases under the rocker 
covers. The negative pressure on that line comes from the vacuum line 
conected at the cold start tube, though a conductance limiting 
orifice.

I never said  a vacuum source wasn't connected to the valve covers, I 
said there was no vacuum under the cover. The vacuum line through the 
cold start pipe does not have the pumping speed to lower the pressure 
in the valve cover/timing cover volume, especially through the orfice 
and with all the outgassing occuring under the valve cover.

In fact, if the large hose is piped to the atmospheric pressure at 
the air cleaner, how can the volume under the valve cover be 
evacuated thorugh the smaller cold start pipe hose and orifice? The 
answer is it can't. Sure, the limited conductance through the small 
hose and orifice would eventually reduce the pressure under the valve 
cover if that area were sealed. But due to the large hose "leak" from 
the air cleaner and the outgassing occuring under the valve cover, 
the pumping speed is far too limited to accomplish this. 

Under normal circustances there is not, and never should be, what you 
would call "vacuum" under the valve and timing covers. Ok, there 
*might* be a slight negative delta P in there but nothing you could 
measure with ease and certainly nothing that would effect manifold 
pressure or engine operation. Frankly, I think the outgassing alone 
over comes the pumping speed of the line, we'll forget about the huge 
hole the hose to the air cleaner represents.

Again, does your engine falter when you remove the breathe hose or 
the entire oil beather? Come on folks, this is basic vacuum 
technology, not to mention basic engine stuff. The D isn't unique in 
this respect.







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