No crankcase vacuum with K&N and flipped lid.

[BushEngineer]

So I had a rear main leak when I put on a K&N. My CDR has a little oil in it so I cleaned it with Dawn and water. With the clean CDR and K&N with flipped lid, I still see only 1/2 inch H20 at 2000rpm. It should be 2-4inches by spec. When I tried reinstalling the paper filter I saw 4-5 inches.

When you guys run a K&N or other are you not running into oil leak issues?

 

[BushEngineer]

My understanding was the crankcase vacuum was purely generated by the venturi effect since diesels dont make intake vacuum. But now my theory is the crankcase vacuum is mostly is due to the intake vacuum caused by the restriction of the air filter and more so the filter housing inlet. Only a small amount of vacuum(1/2 inch H20) is due to the venturi effect at the CDR ports on the side of the intake. While my flipped lid configuration might cause oil leak, I suspect there is a power increase. A K&N in the highly restrictive air filter housing usually results in "no seat of the pants difference".

I suspect the only way around this would be a crankcase vacuum pump. That would allow max power gains of an unrestrictive intake without the oil leaks.

Your thoughts?

 

[Sharecropper]

Interesting. I have subscribed and wondered the same thing.

 

[BushEngineer]

Since last time I only messured crankcase pressure at the dip stick, today I’ll see if I can confirm actual intake and air filter housing pressure.

 

[BushEngineer]

So just tucking the hose into the filter housing, here are the results.

Pressure between filter and housing:
0.25 inches H20 at idle
6+ inches at ~2000rpm

Pressure in filter housing with no filter:
0.375 inches H20 at idle
7-8 inches at ~2000rpm

Now I had a little brain fart as I’m comparing inches of H20 to 14.7 PSI of q ATM thinking I was leaving a lot more on the table than I am. I’m an engineer but it happens.

So 7 inches of H20 is about .51 inches of Mercury or 0.25 psi. So we’re really not costing ourselves much horsepower loss by having just enough intake vacuum to evacuate our crankcase. But that also shows how sensitive our crankcase is to leak(unless my rear main is just on its last legs anyway) and how small of a vacuum pump might be used to do the same job and allow for a freer flowing air filter housing.

 

[swinters]

When we first fielded the CUCV (I was a civilian tech rep for the Army at the time) we had a problem with the hose between the oil filler tube and the CDR getting blocked with frozen condensate during freezing weather and then the oil would blow out through the crankshaft seals and we lost several engines because of it. When they first came out the CUCVs used the standard oil filler cap so GM retrofitted everything with the tall ones you see on them now. The tall ones have a relief valve in them so that if the tube gets blocked the pressure is relieved at the filler cap to prevent oil loss and engine damage. It's not common but they do sometimes fail and open to atmosphere so that's something to at least look at.