Crankcase Pressure Q.

[pyrOman]

There being crankcase pressure in any engine but more so in a stroker and/or a wornout one, is there a practical way to actually measure the pressure to determine what is "okay" versus it being too much?


I'm looking for an actual psi figure besides the obvious puking oil all over the engine!
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[fivelugshortaxle]

Do a leak down test on rings. If they're good them you're good. Strikers need more breathing....stock breathing won't do it.
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[nsracing]

Why don't you hook up a pressure gauge and see what pressure the oil starts to climb out.

[modok]

Sure. hook up a map sensor and data log it or use oscilloscope.
You should be able to see the individual pulses.

But, since nobody else ever does that, I don't know what you will find or if it's normal or not. I don't seem to have a problem with it so you can come over and measure mine for comparison

To measure the blow by volume you can use a fixed orifice on the breather and measure the case pressure. That's done on large engines sometimes but rarely on cars. Once again, it would have to be comparative tho. (no specs for it)

[modok]

Far as 'case pressure"....it's not that simple.
There are multiple things at work

-Windage, due to the moving parts creating airflow inside, which will create an oil mist as well as general chaos inside. The air needs to move around in the case to account for the pistons moving, so that's internal air FLOW

-volume change, due to the rod ratio, at half stroke the internal volume is smaller that at TDC/BDC. This creates pulses, and the pulses and can induce harmonic pumping of some form in the breather system at certian RPMS.

-blow by, which I don't have to explain

[chrisflstf]

You can get a pretty good feel just by putting your hand over the breather cap. Hard to measure with more than a relative feel. Changes with rpm also.

[pyrOman]

[chrisflstf]

U need to invent something to measure it

[pyrOman]

[66brm]

Just use one of those carb sync snails..............
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[jason]

I’d think not much air is from moving parts. As one piston moves in one moves out. Mostly back and forth. 10% leakdown on an 86mm piston is less than 10% of a 94. Do the math. I’d say do a leak down.

[chrisflstf]

It would be nice to know if there is a correlation between poor leakdown numbers and excess crankcase pressure. We can measure 1 but not the other

Maybe a MAF sensor?

[slalombuggy]

[mikedjames]

And another inverse correlation with the total area of all crank case breathers.
And effects from how the breathers are filtered or connected to the air intake system or to outside air.

Which will be different on every engine except for totally stock.

It is probably a measurement you can make on your own engine when it is newly built and then measure it changing..

But the measurements at the source of the leakage are more repeatable - compression/ leakdown tests can be performed and more easily measured with a single connection to each spark plug hole - and it tells you which cylinder has the problem.
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