Miata Turbo Forum - Boost cars, acquire cats. - Another oil catch can thread

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baller. many thanks, sir.

Quote:

Originally Posted by JasonC SBB (Post 574594)

Has anyone actually measured blowby flow and pressure? Examined the blowby routing in the cam cover baffles? I have.

With my old tired 2000 motor the pressure was too high - 20" water at mid RPMs.

I opened the valve cover's baffles and added plastic kitchen scrubbers. I discovered that all the blowby passed through a tiny hole (3/16" IIRC) connecting one chamber to another. I enlarged this hole to a pair of 1/4" holes. This mod reduced the crankcase pressure to about 10".

Before this mod I'd also discovered that the fittings and hoses to my home-made catch can was worth about 7" of pressure loss. Larger fittings helped a lot. The scrubbers reduced the rate at which my catch can filled up.

The problem I was trying to solve was turbo seals weeping when the car was driven hard. The above mods reduced it a lot.

Just for comparison, a stationary turbo diesel setup crankcase pressure spec is <5" water. IIRC aftermarket turbo manufacturers recommend <10".

On my new 2001 motor I measured blowby FLOW and it was a bit over half of what a healthy motor shows. However at redline and full power the crankcase pressure is around 10-15" water. This motor has a stock valve cover. So the pressure is marginally high despite the tight ring seal.

What this all tells me is that the tiny hole that separates 2 chambers in the baffling of the valve cover is too small for when you turbo the motor. Blowby is proportional to power production (and ring condition of course). If you double or triple the horsepower, it stands to reason the that said hole may need to be enlarged. If I now get weeping out of my turbo seals with my new motor at the track, I'm gonna do the same mod I did before.

The reason turbos may weep with high crankcase pressure, is that this same crankcase pressure can cause the oil drain line to back up. If anyone wonders why some turbos don't weep with high crankcase pressure, perhaps it's due to variance in how the drain is routed. In my car, the drain hose has a very slight uphill portion where it passes under the a/c compressor.

Yes I was going to put a big hose on the breather side Then opened it up and realized how tiny the two holes in the baffling of the valve cover were for the breather. If that is the only passage for evacuating blow by then I could really see the dip stick getting blown out with crank case pressure. You cant evacuate pressure fast enough through that small of hole.

The stock breather baffles are kind of cool the way they work. It is designed to where oil condensation will pool up and with pressure pulses and in vacuum situations the liquid gets sucked back into the head while gas can escape.

The baffles on the port that attaches to the PCV sort of suck for doing oil separation. And I think Oil will slosh into it especially during hard acceleration in a left hand uphill turn. I am pretty sure turn 5 and 6 at Laguna were causing oil to pump out that side and fill my catch can.

My current plan is to enlarge the holes in the breather side baffles So it is equivalent to a -8 AN line and route it to a VTA catch can breather. What was the PCV port in the valve cover will be connected by a hose to the pan above the oil level. This line will be routed through a swirl pot/ oil separator of some sort wit an additional line hooked up to the VTA catch can breather as well. Probably use all -8 lines but with a -10 line down to the pan.

Now I just need to figure out what will work for the swirl pot/oil separator to keep the liquid oil that splashes from the PCV port and the pan port from filling up my catch can breather.

Bob

Quote:

Originally Posted by levnubhin (Post 574625)

Update: It's been almost 2 weeks and everything is working perfectly. I think the biggest help is having that crank case vent.

Dam it now I am thinking I want to add that port in a 1.8 block. Just drill and tap it some how. I’m thinking that must work much better than going to the pan It is high enough it must non be getting too much oil slosh in it. It is also big like 5/8” so it should really keep pressure from building up in the crank case.

Bob

just got this http://www.summitracing.com/parts/SUM-120108/
i will give it a shot.

I don't see why adding a vent to the block is better than a vent in the cam cover ... ?? Especially by modifying the existing baffles. The holes that connect the block airspace to the head airspace are huge.

EDIT:

Quote:

Originally Posted by bbundy

I think what happens if you only vent the valve cover and vent it well, as in better than what you can get from a PCV system, is the pressure and gas flow from the bottom end generated from blow by has to go back up to the top of the head through the oil drain back passages if it gets too much it will impede the oil trying to drain back from the head to the pan and basically cause much of your oil to get stuck in the top of the head where it can slosh up into the upper vents or even possibly cause an oil starvation issue.

I thought of that too but it seems a stretch.

Quote:

Originally Posted by JasonC SBB (Post 574698)

I don't see why adding a vent to the block is better than a vent in the cam cover ... ?? Especially by modifying the existing baffles. The holes that connect the block airspace to the head airspace are huge.

EDIT:
I thought of that too but it seems a stretch.

Because the pressure can't get from the crank case to the cam cover quick enough. You end up blowing out seals instead.
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BTW a good motor will have a blowby cfm that is 1/50th of the hp output.

A 300 hp motor will have 6 cfm. That's not huge. I have a flow gauge and I can blow nearly 15 cfm with my lungs. I can't imagine that blocking the oil drainage given the head flow rate, and the size and # of holes in the head. Think about the tiny oil hole that supplies the head and the # and size of drains.

Quote:

Originally Posted by levnubhin (Post 574708)

Because the pressure can't get from the crank case to the cam cover quick enough. You end up blowing out seals instead.

Think FLOW not pressure. Pressure loss comes from the flow resistance of the holes.

I happened to measure crankcase pressure 2 ways: by attaching a hose to the cam cover PCV hole, and by attaching the hose to the dipstick. Same pressure read. In both cases the blowby was flowing out the hotside cam cover vent. This says that the holes between the block and the head aren't restrictions to the flow.

When I blow through the tiny hole in the baffles I mentioned, the resistance I feel is huge.

Do you have pics of your baffles? stock and modded?

Both of mine have openings on them this size:
http://i158.photobucket.com/albums/t...t/IMG_2061.jpg
which is far larger than the vent exits at the cam cover. And there's at least that much area around each baffle when installed in the chamber.

Quote:

Originally Posted by JasonC SBB (Post 574698)

I think steady state average flow rate and the turbulent pulsating flow as seen in the crank case due to the pistons going up and down will produce significantly different behavior in how the oil drains back from the head.

Bob

When I pour my Hawaiian Punch, I make sure to punch a vent hole.

Quote:

Originally Posted by m2cupcar (Post 574739)

Do you have pics of your baffles? stock and modded?

Here is the idea but I took the foamy thing out (too restrictive) and switched to plastic wool.

http://pages.sbcglobal.net/jcuadra/c...er/stuffed.JPG

I have to go find the pix of the hole.

Quote:

Originally Posted by devin mac (Post 574641)

so, to summarize: you vented the blocked off port on the passenger rear of the block to a small'ish catch can, ported the two standard VC vents out to larger (-10AN equiv) openings, and ran both of those to a second, larger catch can. no internal mods (aside from porting out the vents) to the valve cover baffling or valve cover itself, correct?

I'm looking to get my car up and running again and i know i was struggling with some crankcase venting issues at 17psi when i put it away, so i want to get it right the first time, this time.

Does anyone have a pic of this port on the back of the block? I'm going to set up a catch can on my car, and was just going to port the two valve cover outlets to a breathable catch can.

In my 69 Buick, the big block is known to have oiling issues. The oil drains from the head to the block are too small from the factory. It's standard procedure to open these up larger. I wonder if our motors would benefit from the same treatment. Would it help the head oil drainage reducing the effect of the added blowby pressure?

Quote:

Originally Posted by cueball1 (Post 580775)

I just drilled and tapped a 1/2" pipe thread hole in the side of my block it comes out just behind the oil squinter on #2 same location that some of the early 1.6l blocks have a breather boss cast in from the factory I attached a -10 hose to it.

I am feeling not much steady state flow but there is defiantly pretty good pressure pulses even at idle. This is on a stock motor with good compression numbers but boosted. This goes back to my theory that pulsed flow even at low average pressure difference and flow rate contains so much more energy than steady state flow that it crates quite a different behavior in how it will push liquid around in a gaseous environment.

I was going to hook the line to the side of the block it to an oil separator of some sort then to a VTA catch can but right now I just have it hooked directly to a VTA catch can. It seems to collect mostly water vapor so I think this location in the block works pretty good as a vent without getting much oil.

Bob

I stumbled on this pretty good document on blow-by and breather systems.

http://www.106rallye.co.uk/members/d...hersystems.pdf

I still think I’m going to stay Vent to atmosphere but I plan to engineer the system well. I want to make a volume separator to fit in line before a Vent to atmosphere catch can.
I think the big problem with the stock system is it just dosnt work well when you making several times the stock hp.

Bob

So would tapping the pan on a 99 engine not be a good idea? I have my engine out right now to reseal the oil pan so I was going to make a return for the catch can. I think thats how the MSM is setup from factory as well.

Quote:

Originally Posted by cryogenic (Post 581566)

I think The MSM runs the return below the oil level all the way to the bottom to make sure it is submerged in oil. Works good as a return but not so much as a vent I would think.

My experiance is there is a lot of oil slosh in the pan with hard cornering and braking. My port in the pan high and just below the alternator didn’t work so well. In some situations it would pump oil out. I assume it would slosh up covering the port and pressure pulses would give it enough momentum to shoot oil all the way up the hose. Maybe there is a better spot in the pan that would work I do not know.

Interesting I found this site which sort of describes the breather system on an Escort RS or Sierra Cosworth. Again breather port up high on the block. I think the early 1.6l GTX in European rally trim came with a similar setup and it was cast in the block.

http://www.wrc-cosworth.org/howto/br...separator.html

Bob

The pressure pulses in one end of the crankcase may be the pulsing from the nearest cylinder. Remember that air pumps back and forth between cyl 1&2 under the pistons because they alternate, and between 3&4. This is why it is recommended to enlarge the holes in the webbing in the block near the main bearing caps, between 1&2, and between 3&4. These holes are much smaller than the bore diameters.

In the cam box, there would be less of that pulsing.

AFAIK the WRC Escort Cosworths had a venturi device connected to the turbo and the crankcase then venting into the exhaust pipe. Under load the turbo blows into the venturi device thus creating vacuum in the crank case. The goal is to create vacuum in the crankcase and the turbo cars can achieve it without a separate mechanical pump - just use the turbo to do the work.
Most likely the current WRC cars use similar systems

Quote:

Originally Posted by bbundy (Post 581571)