4AGE crankcase pressure - whats normal?

[Vertigo]

Im about 3000km in on my rebuilt smallport, and its runnig exceptionally well - really stoked, it appears I did things right!

The only thing I need to sort out is that it seems to have fair bit of crankcase pressure. Taking the oil cap off results in fairly vigorous wind being generated, as in, a piece of paper over it gets blown up pretty forcefully. The breather port in the intake manifold was blocked off by previous owner for Reasons of Boost, so Ive routed the cam cover outlet to a catch can via a length of mediocre piping. I intend to redo this before boosting to my target.

Anyway, what is actually normal for a 4AGE smallport? Especially one with only 3000km on it.

Also, whats normal for one boosted to 15psi?

Have my rings not seated properly? Worth noting that the engine does not use oil. Valve stem seals?

[iOnic]

Do a leakdown test. I would be doing one at this point after a rebuild anyway.

[jondee86]

Anyway, what is actually normal for a 4AGE smallport? Especially one with only 3000km on it.

Another one of those questions for which there does not seem to be any sensible answer.
So, in the interests of science, I shall conduct some experiments I have a smallport in
my car; one which has done something between 90 and 100,000 km, and appears to be in
good running nick whith no known problems. Just have to think of a way to measure blowby ?

And blowby is minimum at idle, increasing with engine load and rpm. Boosting the engine
to 15psi should close to double your power, and that will most likely double your blowby. It
is very common to see high power 4AGE engines running two intake side cam covers and
two vent hoses to a catch can. That's an simple way to get double the vent capacity.

The original smallport cam cover vent went to the side of the intake manifold, and then
ran via an internal channel thru the throttle body and exited in front of the throttle plate.
There was a small pinhole vent from the internal channel into the intake manifold, but
I don't know its exact function. My intake manifold has been cut-n-shut which renders the
internal channel vent null and void, so I currently vent to atmosphere which makes it easy
to know how much blowby I have.

Cheers... jondee86

[Vertigo]

Would appreciate it! Would it be worth coming up with some kind of venturi effect inches-of-water device to place over the oil cap or breather port?

[jondee86]

A made a small video as scientific testing is not so easy...
https://www.youtube.com/watch?v=kZNlBJi ... e=youtu.be

Engine was fully warmed up and idling around 950 rpm. Even at idle they flick
a bit of oil out the filler so I wasn't keen to be revving it up !! You can see that
the filler cap bobbles around when sitting loose... that is normal as far as my
experience goes. The ping pong ball, being lighter, bobbles around a bit more
vigorously, but does not hit roof.

When you put your hand over the filler you can feel the air pulsating until the
palm of your hand is about 300 mm from the filler opening. After that there is
just a tiny breeze feeling. Same with the cam cover breather that I tested last,
except that the pulsation can no longer felt when your hand is 150 mm away.

The pulsation is very evident, as you can hear when I hold the ball down with
my finger And it is possible to mistake the pulsating air for a strong constant
flow. But it is not. Those are pressure waves riding on a very small actual
airflow. If the airflow was really high the breather hose would blasting my hand
much further away than 150 mm.

While it is true that blowby will pulsate as each cylinder fires in turn, I think
that it is very possible that air being pumped around in the crankcase by the
movement of the pistons is the major contributor. Sure, as two pistons move
up the other two move down, but the energy required to get the air to "jump"
from cylinder to cylinder will also cause a pressure fluctuation throughout the
whole of the engines internal volume.

I've never seen any real explanation for the pulsation, so that is my homegrown
theory. If anyone has a better one... post it up

Cheers... jondee86

PS: All the rags and blocks of wood were to catch the oil and make a wind break
to stop the breeze from the fan blowing the ping pong ball away !!

[Vertigo]

Oh my god, the ping pong ball is a great idea. We can totally make this a standard measurement, lmao.

Ill come up with some sort of DIY thing that can be made very easily. Will also try as you have done to compare, ill post a video too.

[whynot]

Simple idea. Use a clear tube which the ping pong ball fits down. Use an easy to obtain size. Then drill a line of holes a set distance apart going up the pipe say 4mm holes 10mm apart over a 300mm length. Should be easy enough to make and really cheap as well.

This should give a repeatible indication of blow by and ignore the pulsations generated by the pistons moving. Any other ideas guys?

[RomanV]

I've got a spare map sensor for datalogging purposes hooked up to my ECU.

I plumbed a vaccum line into my catch can and found that although there was flow through it, pressure build up (or pressure drop) was nil through the whole rpm range etc.

I didnt measure directly from the crank case though, but it seemed a non issue.

You could maybe get a spare oil cap, drill a hole through the middle and hook it up to a manometer (fancy word for a big pipe filled with water) and see if there's any pressure gain or loss when the cap is on.

Just dont suck the water down the cap haha.

[jondee86]

Just dont suck the water down the cap haha.

In the video the ping pong ball bounces quite violently from time to time
when it hits the edge of the oil filler opening. But in the odd second when
it is relatively stable, you can see that it sits well down in the opening.

The bouncing is caused by the ball actually being alternatively pushed out
and then drawn back into the filler neck... a result of the pressure variations
from the pulsation. When it is drawn back into the opening and hits the side,
it pings off at an angle, eventually escaping from the filler neck.

If the ball could be restrained from moving horizontally by some loose fitting
vertical wires forming cage, I would expect the ball to sit quite close to its
"seat" in the filler opening, and oscillate up and down by a few millimetres.
The mid-point of the oscillation measured from the position that the ball
sat with the engine off, would be a measure of the blowby volume.

How to calibrate that in terms of cfm, l/min etc would be another question

Cheers... jondee86

[RomanV]

Doesnt need to be transferred to another unit of measurement, if "mm of pingpong ball travel" verifies the problems and can show you changes for better or worse if you try to fix the issue.

mm of Pingbong ball travel might already be a standard unit of measure in Thailand, but you might not want to google that while at work

[Stu-]

^Gold.

[jondee86]

Aparently these women are graduate engineers....



... because I believe that this guy was after the same information

Cheers... jondee86