Turbo Engine Blowby, High Load, Sustained High RPM

[Buddyworm]

Hello all, my first post here is a question that I'm hoping the experienced and knowledgeable folks here can shed some light on for me. I come at this from a drifting background so I'm hoping SWR makes his way in here to give some input as I do believe he's been involved with Frederic Aasbo's builds.

My own engine is a Twin cam 4-valve 1.8L turbo, ~8.5:1 CR making 350HP and it loves to fill catch cans while drifting. Engine still compression tests well and shows no signs of knock physically, or on my knock monitor. I've even gone so far as to cut big chunks out of the timing map at the track with no change in the amount of oil it blows out the breathers. AFR's sit around 11-11.5:1 when on the drift track. In my case this is on 94oct RON+MON/2 gas.

Interestingly, the engine does not push oil out the breathers when I'm just rowing through the gears at the road course or on the street. Only sustained high rpm and load.

It's become commonplace in the high-level, wet sump, race gas competition builds (Formula Drift) to have high volume catch cans that drain back into the pan. Some examples:


3.4L 2JZ, big "self-draining" catch can. Allegedly capable of 900hp


Boosted LS3, "self-draining" catch can


Big power 2.4L 4banger, Turbo and spray, "self draining" catch can

So what does everybody think? Are we dealing with abnormal levels of blowby for the RPM?

Are we seeing a normal level of blowby that's building up in the crankcase faster than it can vent due to the sustained high RPM? And picking up more windage oil on its way out?

Are the rings starting to flutter and we're holding them at the RPM where they do so, hence losing seal to the cylinder walls?


Thanks for the input all! Been lurking for a while now, it's nice to finally participate.

[peejay]

If you even have .5% blowby on a 500hp engine, that's 2.5hp worth of exhaust blowing past the rings.

I've seen some remarkable wind blowing from the breathers on otherwise tight sealing engines running at high boost.

[Cubic_Cleveland]

What engine are you working with and what rpm is "high rpm"?

I think you could be on the right track, crank case pressure is building quicker than you can vent it and drawing oil along for the ride. What size are the breathers and how's the baffling? There also might be some clues in sump design.

[ijames]

It's late and I'm really tired, so I'm going to unlurk a bit and suggest something off the wall - the sustained rpms when drifting fills the valve cover with oil and you are getting blow-by past the intake valves that is bubbling through that oil and sweeping it out the breathers. As theories go, it's got some good points. It's a leakage path that won't show on a blowby test, and you aren't getting any detonation which I think you would be if the blowby was going past the rings because some oil would surely be going upwards some of the time. On a drag strip it's all over in a few seconds, and on a road course you are on and off the throttle and cycling the rpms up and down constantly so there's much more time for drainback compared to drifting. Would be interesting to put separate lines to separate catch cans on the valve cover and anywhere lower on the engine that you can, to see where the oil is coming from. Even if the airflow isn't coming past the intake valve stems it must be some kind of windage and/or lack of drainback issue that gets the oil up to the breather lines so it can be swept out. Well, hopefully it's at least an amusing idea, I'm going back to lurking and learning.

[modok]

You probably need a more effective breather system.
Most aftermarket "systems" I see are very crude, and not very good.
Venting the engine:
Simple form, using a breathing location on the engine with the least oil mist naturally, your are using the engine itself as a mist filter. It can work, but as internal windage gets greater that may not be enough, then next logical step you put a baffle system in the valve cover or wherever there is room for it, and some of those baffle systems are quite impressive, and go unnoticed, until some fool puts on a aftermarket valve cover LOL, but if that isn't enough then what?
Then you make an external mist filter. Just using a "big box" is good to keep oil off the track in the event you ventilate a piston, and that's good for everybody else, but not good for you.
The difference between a barf box and a mist separator would be the separator is made to remove the mist and then drain back sto teh sump, not HOLD it, so it will have a drain, and it will have some scheme to do this. Centrifugal is a simple but useful idea. Simple form you use a tube vertically, have the vent lines from engine come in at a tangent in the middle(so it swirls), at the bottom is a drain line, at the top is the vent. There is a specific corner of engineering about cyclone filters, to work best the proportions and velocities need to be looked at, but good news is even if you are way off it still works suprisiingly well, but not as good as dyson vaccum LOL

The funny thing is, building WET FLOW intake manifolds, we want to keep the mist SUSPENDED, then build a breather we want the mist to fall out, and many of the same rules apply. The worst intake manifold ever would be a good breather box, and the worse breather box would be a good intake
Mist flow is also an issue with stills, which we use, you know, for "fuel"

[user-23911]

You'll know what's wrong with it when you pull the pistons out.

To me it's just the usual turbo problem.......knock monitors that don't work and broken ringlands as a result of it.

Catch cans are only for broken engines and compression tests don't pick up on broken ringlands, if anything the numbers are a bit higher
Checking the plugs ALWAYS works.

[Sparksalot]

So, high sustained G forces and RPM cause your engine to puke oil? Do you know about the history of racing and the evolution of engines and lubrication systems in land based racing? You have the greatest of opportunities for complete loss of oil control under your operating conditions: a wet sump and breathers as a means of "control." We learned all of this from WWI and WWII aircraft engine designs done long ago by genius designers. Study at their feet for a long while and prosper. It's all in books.

They made upside down V-12s work just fine. Get your study on. Your engine will benefit.

We made CanAm unlimited race cars with clones of those WWII engine lubrication systems and boy howdy they worked just fine thank you.

[mag2555]

Was there ever a time when the engine did not do this , like when it was making far less HP?
I think a clue resides in there !
Anyway a motor like this needs a custom made crank scraper that is lined with Teflon.
It should be set up to rub lightly and it will ware in with no issue and provide less then ,010" clearance when that has taken place!

[Kevin Johnson]

...
Interestingly, the engine does not push oil out the breathers when I'm just rowing through the gears at the road course or on the street. Only sustained high rpm and load. ...

While drifting?

[ptuomov]

Controlling oil flow and controlling gas flow are two related but separate problems.

One thing to consider is where to vent the crankcase gas out of the engine. With high g-forces, I think you have to go thru all operating modes one by one. That's what we tried to do (with a street car, no drifting there, or inverted flight!), and had some success. For example, when accelerating hard under boost, you probably want to vent the crankcase gasses out of the front of the engine. When braking hard and under manifold vacuum, you probably want to vent the engine from the back of the engine. This is because the oil sloshes to the back of the engine under acceleration and to the front of the engine when braking. Under lateral G's, you want to vent from the inside side of the turn, maybe with a two-inlet one-outlet gravity ball valve like in the piston airplane inverted flight systems.

I wrote a couple of posts on our system here. It would be completely inadequate for your use, but maybe you'll get some ideas from there:

http://rennlist.com/forums/928-forum/56 ... st13127650
http://rennlist.com/forums/928-forum/56 ... st13127650
http://rennlist.com/forums/928-forum/56 ... st13128484
http://rennlist.com/forums/928-forum/56 ... st13128486

[MadBill]

A simple system to achieve such 'switching' was credited to the Petty operation ~50 years ago. He/they built a U tube that straddled the L&R rocker covers with a tee fitting in the straight transverse portion, which was a very loose fit over a large (1" or so) ball bearing, but the curved-down ends were 1" OD so on a left turn the ball rolled to the right, sealing off the outboard cover and vice-versa.

It would be a bit Rube Goldberg, but if necessary, such a rig could be plumbed not into the rocker covers, but into a pair of similar longitudinal breathers joining the front and rear of each cover.

[peejay]

Found it.

http://www.bufkinengineering.com/Catch%20Can.htm

An interesting approach to crankcase breathing that evolved through trial and error and analyzing the situation. Went from filling a catchcan in less than one track session to nothing but a little oily water vapor.

[wyrmrider]

On water cooled VW Vanagon we stuffed stainless scrub pads in the vertical oil breather tube to slow down the velocity, sorta like the materiel in an old bath air cleaner, figured it turned little drops into big drops which would then run down
do you have a baffle under your breather hose hole

[Kevin Johnson]

He is waiting for Bjorn. I PM'd him.

[ptuomov]

A simple system to achieve such 'switching' was credited to the Petty operation ~50 years ago. He/they built a U tube that straddled the L&R rocker covers with a tee fitting in the straight transverse portion, which was a very loose fit over a large (1" or so) ball bearing, but the curved-down ends were 1" OD so on a left turn the ball rolled to the right, sealing off the outboard cover and vice-versa. It would be a bit Rube Goldberg, but if necessary, such a rig could be plumbed not into the rocker covers, but into a pair of similar longitudinal breathers joining the front and rear of each cover.

You don't need to do that in the front-back direction, I think. I think you can just use manifold vacuum to went from the back and compressor inlet to vent from the front of the engine. The manifold vacuum is there during deceleration and the compressor inlet vacuum is there during WOT. Left vs. right side venting could use that ball valve in an inline engine, I think.