thinking about blowby

[sle2115]

One of the other issues and reasons that this nets such gains on a race engine is RPM and windage. By keeping a negative pressure on the crankcase of an engine spinning 7-9000 RPM's, windage is reduced...windage screens are used as well as crank wipers to keep the "stirring" of oil to a minimum on these apps. While I'm guessing our cranks prolly stir the oil, the net result on an engine turning 3500 RPM would be much less than one turning 2 to 3 times that. That's not to say that evacuating blow-by might not be a good idea.

Since diesels in general don't make much intake vacuum (open intake plenum versus a throttle plate on a gasser) I don't think plumbing directly into the intake would do much unless it's done in a way that air flowing over the "port" would cause vacuum such as the angle cut crankcase evac system plumbed into the exhaust where the flow of exhaust causes a low pressure as it flows over the pipe, thus creating vacuum.

Also keep in mind that a positive crankcase evacuation is as much a form of emissions control on a gasser as it is to benefit the engine. They would rather draw the vapor into the intake and run it through the combustion process than vent to atmosphere as they did in the old days. Anyone else familiar with the old V8 SBC engines and the "slobber tube" system they used to use? It was a slant cut pipe that ran from the intake valley to down just below the engine, as the car moved down the road, the air flowing under the car created the same negative pressure as the pipe in the exhaust, thus producing postive crankcase evacuation.

 

[DeepRoots]

thanks Sle, I was hoping you'd come in.

I'm gonna try hooking it up when I get home just cuz.
The only other part I would need would be some sorta restrictor/breather on the valve cover to limit air flow through the engine so I don't loose power brakes.

 

[RLDSL]

If you get too much vacuum on the breather system it will suck the oil right out of the crankcase, baffles or no baffles. If you get to pulling too ******* it, it messes up the balance and instead of drawing off vapours, you start drawing off condensed droplets and you can begin to empty an oilpan pretty quick without realizing it. It's that balance that the factory engineers beat their heads over for weeks at the dyno designing the factory breather system to get.

 

[DeepRoots]

I encountered that RLDSL when I used the stock ATS turbo breather area. Lost a quart of oil every 100miles.

Getting the air from the timing cover seemed to solve the problem as I can drive 10k miles with no oil loss of significance.

 

[oldmisterbill]

Anybody have a flexa straw.
On a serious note this is quite interesting.

 

[david85]

Negative pressure in the crank case is definately a good thing to have. If nothing else it prevents oil leaks. But doesn't the CDR only restrict flow at higher RPMs as relative vacuum from the engine intake increases?

I don't suppose any one has actually measure crank case pressure before?

 

[DeepRoots]

I have indeed. I can't recall what it was, but International has a spec.

Basically you block off the CDR and measure the pressure with a Manometer at the dipstick.
I bet Icanfixall has the specs.