Crankcase breather, blowby, windage

[mdburchette]

Good rings will not generate significant blow-by, the small ring gap should 'choke' under high pressure and not flow at all. Engines tend to breather more at low load. If you want very low blow-by all the time, use Total Seal rings.
GC

I've decided to show my fancy breather just to attest to Guy's response to Total Seal rings. This is after 2 1/2 years of running around town and running the engine at 8000 rpms while autocrossing. As you can see, not much blow-by.

[Infectus-Guy]

I've also been pondering this subject whilst tidying the plumbing under the bonnet of my integrale evo. I've decided to fit a catch can to reduce the amount of pipes, but i've also heard that enough oil vapour will actually lower your octane rating. I'm not really bothered if this is true or not, but it'll be nice not to have the oil return hose looping back round the front of the engine again. Not sure how this fares as far as MOT's go, but i'm sure we all know at least one sympathetic tester!
Guy

[Evodelta]

The integrale Evo 16v already comes equipped with a catch tank - very efficient it is too! It's the 8 valve model that is not such a good design.

[Infectus-Guy]

The integrale Evo 16v already comes equipped with a catch tank - very efficient it is too!

yes it does the job, but as i said there's too much plumbing there for my liking. The oil return hose had split right open and had been dripping oil all over my gearbox for what looked like a very long time. I'm after the type where you tap off the oil when you see it on the level and has a filter to get rid of the gas. With integrales you have a couple of choices where to vent it, i'll probaby just vent it near a bonnet vent because i've ripped out and blanked off the heater.
I'd always wondered what racing teams do with their crankcase breathing and Guy perfectly answered my question.
Guy

[Os7213]

Hi

Like always interresting thread
I have think about oil fumes and I was wondering if the breather hose can be bypassed in a modifed oil cooler to keep a little bit more pressure in the crankcase?

I've start some research and suppose that the small cooler can be place at the front, use fresh air to cool oil fumes (Not sure yet if oil fumes can leave more particles due to air temp variation this can be a major problem...but the temperature can be "controled" by adding a plate) and oil cooler internal shape to keep stable pressure, for now I cannot find any infos on it but I have a spare transmission oil cooler I will "test" with compressed air to see what happen!

Since I dont have too much knowledge about the subject I "suppose" It can work..
What do you think about it?

Thanks everyone
Hugo

[7t5-27]

Temp does have role in how many particles a given sample of air will hold. Whether (or more correctly how) this will effect the oil in the crankcase vapor would have to be seen, but you can look at it like this, in the morning with cooler temps the air holds more moisture (humidity) up to the point of saturation (dew point, if temp falls below dew point you get fog, common in england?) as the day goes on the moisture content will drop as the air temp increases due to solar heating. With this in mind then it might actually do better to keep it warm. As for pressure (in a closed system) as the temp rises so does the pressure, again maybe warm is better than cool. HTH

Greg

[Os7213]

Ok

Thanks a lot Im now understanding correctly the effect of air temp...
I just begin to read about the effect so any help is appreciated!

So I will ask the same question if I stay with a small oil cooler, placed anywhere else then at the front to keep more pressure with warm air, do you think the cooler alone can help to keep more pressure due to the internal desing?

Thanks again
Hugo

[7t5-27]

If maintaining a given pressure in the crankcase was the goal run the breather hose to a presure relief valve preset at a given value. Above the value the pressure is released below it is maintained. Should work (works in theory any way). hope that helps, Be Safe

Greg

[sumplug]

High crankcase pressure = lost power.
I know in F1, they have a complicated crankcase relief pressure system that gives them more power.
I remember on the old Fiat 128 type SOHC engine, we ran the crankcase hose to atmosphere, and it seemed to help power!!

Andy.

[Kevin Johnson]

Lowered sump pressure allows you to run light tension rings which reduces a large amount of friction + more power available. Significant gains available. You'll need at least a steady 5" Hg drop in the engine crankcase to activate them.

Optimal level for sub-F1 level engines appears to be 10". At say 17K rpm even small amounts of atmosphere can cause significant losses. The figure I heard was that about 8% return on peak engine power was available in F1 -- expensive to achieve that, though, but very believeable. NISMO reported that the mere presence of the girdle structures in the KA24DE and SR20 created a 5% windage power loss.

Reduced atmosphere means reduced windage effects which will also reduce parasitic losses (ala the Nissan engines above).

Better oil condition -- less entrained air.

David Vizard commented on the exhaust extractor systems -- they work well at full throttle but not partial openings. Insufficient mass and velocity of gasses to generate a good Bernoulli effect. Also, this is probably unwise with light tension rings as many engine blowups occur when the gas is let off -- this will also be a condition to allow oil to pass by the rings (lowering octane rating) and encourage detonation in highly tuned engines. Just spoke with a top level builder here and many guys are using the aux vacuum pumps from old BMWs. I don't know what the longevity is in months or years of steady running in oil vapor rich environs is but for the racer -- heck, why not. I was surprised they could draw enough volume given blowby percentages but I think we are talking professionally built engines with very low percentages of blowby.

Of course all this is specifically illegal in some classes precisely because it does work.

[Georges Fonso]

Yes, depression will help a firing cylinder because the piston is forced down by the pressure differential between combustion region (high P) and crankcase (much lower P), and a piston on the intake stroke. But what about a piston that is trying to evacuate the cylinder on ex stroke, or compress on the firing stroke. Will it hold it back? Well, it would tend to wouldn't it?

I would suggest that the pressure differential between combustion region and crankcase will not affect power because of "sucking down" or "pushing up" the pistons. Let's not forget that, for every piston "sucked down" on its way towards BDC another piston tries to go up towards TDC, so one cylinder's gain is the other cylinder's loss and vice versa -- in other words, the crankcase pumping effect nets to mere nil...
The way I see it, crankcase depression *might* be a good thing because:

1. It *might* reduce hydrocarbon oil contamination because it gets rid of fuel vapor in the crankcase before it has enough time to mix with the oil
2. It *might* help the rotating assembly to throw away the oil from its surface a bit faster that normal (even though i'd say that such a claim is probably overstretching the point :?: )
3. It *might* reduce oil frothing in the sump :?:

However, I' m convinced of one certain benefit, occurring during the induction stroke, especially on engines with poor sealing: that is less contamination of the incoming charge with oil vapor. This means better Volumetric Efficiency (if one has improved the engine to such and extent that it will show any power gains due to this) and, of course, less reduction of the fuel mixture's octane rating.

G.F.

[Guy Croft]

I'm easy on this issue.

But certainly the answer to an engine that has high blowby - is rebuild it.

GC

[Kevin Johnson]

I would suggest that the pressure differential between combustion region and crankcase will not affect power because of "sucking down" or "pushing up" the pistons. Let's not forget that, for every piston "sucked down" on its way towards BDC another piston tries to go up towards TDC, so one cylinder's gain is the other cylinder's loss and vice versa -- in other words, the crankcase pumping effect nets to mere nil...

Nil if there is a vacuum, otherwise bay to bay pumping losses are still present. The mention of wrist pin issues sometimes emerging at 15" means that oil spray patterns from the rods and mains are reverting to their ideal. This indicates windage is not dispersing the oil to the side walls of the cylinder in sufficient quantity to lubricate them via the scraper rings. This suggests 15" is a practical limit for most race engines, F1 excluded. For wet sump engines you must also remember the effect on the oil pump.

The way I see it, crankcase depression *might* be a good thing because:

1. It *might* reduce hydrocarbon oil contamination because it gets rid of fuel vapor in the crankcase before it has enough time to mix with the oil
2. It *might* help the rotating assembly to throw away the oil from its surface a bit faster that normal (even though I'd say that such a claim is probably overstretching the point :?: )

Per 2., depression reduces the pressure differential that forms around the rotating assembly. This releases oil drawn into the cloud -- this effect is orders greater than the surface adhesion of oil. This because oil entrainment rises as a function of crank rpm. Less atmosphere leaves less working mols for pressure differential formation. Conversely, forced induction engines generally have higher atmosphere levels and so higher windage effects.

3. It *might* reduce oil frothing in the sump :?:

Definitely.

[Georges Fonso]

-Kevin,
Hi! I say you've got some points, there...

The mention of wrist pin issues sometimes emerging at 15" means that oil spray patterns from the rods and mains are reverting to their ideal. This indicates windage is not dispersing the oil to the side walls of the cylinder in sufficient quantity to lubricate them via the scraper rings. This suggests 15" is a practical limit for most race engines, F1 excluded

Could you please expand a bit more on the above, never heard about that sort of wrist pin issues before...
Thanks!

-GC,
A rebuild is most definitely the solution, but what do you do when a new customer comes to you with a freshly built and expensively paid for engine, and a breather which is smokier than a two-stroke scooter? Yet, the mysterious lot of expensive parts and ubiquitous machining/ "blueprinting", puts out some rather decent power... For the moment, the owner skips on the case with fresh "heavyweight racing oil" and a quart of honey-like "no-smoke" oil additive -- I want to slap him for this, I bet you'd like too...

G.F.

[Guy Croft]

Well,

re what I do when I see such a case (and keeping within my own strict Protocols) I would not 'slap him'. Metaphorically perhaps, no more than that. But I can tell you I do handle a LOT of such cases.

My answer is always the same. 'You should have got me to do it'. The answer is always the same, 'I wish I had'. I then say 'you better get it up here'. They sometimes do and Flex-Hone of correct type, coupled with the most diligent detergent cleaning regime and re-ring would be the norm.

I would simply not give any other advice , ever, to anyone who had an engine breathing in the manner you describe.

GC