Crankcase breather, blowby, windage

[Georges Fonso]

Always metaphorically speaking, GC, for sure!

Speaking of FlexHone I'm tempted to veer a bit off topic, please advise if I should open a new one in the General Discussion Forum.

[Kevin Johnson]

-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!

G.F.

Some builders have run into this problem. Many engines do not have dedicated piston squirters or direct gudgeon pin oiling provisions from within the piston rather than from the skirts/scraper-rings.

Assuming pin oiling has heretofore never been a problem for whatever hypothetical engine is in question, the drawing of a heavy sump vacuum can lead to this surprising result. I think it is easy to remedy and so just something you need to be aware of and plan for.

The easiest solution for common rods that I know of is to create vertical slots in the side faces aimed straight up the beam. This is an old trick for cooling the underside of pistons in aircooled motorcycle engines. Sometimes you see these same sorts of slots in OEM rods aimed at the thrust bearing surface of the cylinder.

[Guy Croft]

I can tell something about the issues referred to above.

1. The reason for having pin-oilers (fed from the oil control ring) on racing pistons (most do) is to feed the wrist (gudgeon) pin. That oil lubricates the pin bore in the piston and the rod. Although production cast pistons may not have these drillings (and to be honest would be weakened severely if they did) they do seem to survive perfectly well on 'splash' and draining oil (pulled off by the 2nd, scaper ring) around the underside of the crown. Hot oil readily works its way along the pin to where it is needed.

2. I can tell you with a fair degree of certainty that oil spray to piston underside is used on production engines to prevent detonation (n/a and turbo engines) and to control piston temperatures in the upper section and thereby also contribute to reduced emissions. Moreover if the piston runs cooler (thereby) you can also run tighter bore-piston clearances, giving a quieter engine. Although this may seem odd achieving low drive-by noise levels is extremely critical to car manufacturers and every little really does help.

3. I don't much go for third party info, but in this case I have reliable evidence from a reputable race engine builder very well-known to me, who has done back-to-back dyno tests on this very thing. He told me that on normally aspirated 16v 2 liter Ford he had built for oval and was testing (highly tuned, too) that using oil sprays to the piston underside gave definite power loss. He removed them.

Surprised? I was. I suppose to be 100% certain, you would have test individual engines to prove that one out, really. But it would make me very circumspect about recommending to get a power gain! When I worked on F1 engines (Hart) they had oil sprays, but in those cases if there had been none, there would have been almost no bore/pin lubrication at all, so well evacuated was the crankcase by the advanced, high depression dry-sump system.

4. As far as bore/skirt oiling is concerned you can definitely run an engine (I have done it) with no spray oiling to the cylinder walls at all. I am not saying this is ideal, but when I ran my own race engine like that (highly tuned 1800 TC Fiat) for over 3 years there was no ill-effect whatever. I'd know. This is because there is tons of oil throw in there from the crank (and my engine was dry-sumped) and vapour that will do the job fine. you can spot a bore with poor lubrication a mile off, vertical scratches all over the bores and on piston skirts, shiny/glazed bores with all the cross-hatch gone...

GC

[Kevin Johnson]

3. I don't much go for third party info, but in this case I have reliable evidence from a reputable race engine builder very well-known to me, who has done back-to-back dyno tests on this very thing. He told me that on normally aspirated 16v 2 liter Ford he had built for oval and was testing (highly tuned, too) that using oil sprays to the piston underside gave definite power loss. He removed them.

Surprised? I was. I suppose to be 100% certain, you would have test individual engines to prove that one out, really. But it would make me very circumspect about recommending to get a power gain!

The decrease is probably in large part from windage losses due to the extra oil being caught up around the rotating assembly. This is also why crank scrapers are common place in Formula Ford and are (now) also restricted by the SCCA as power adding devices. Typically there is a 2% to 3% gain on a NA engine. In fact, the SCCA now specifically prohibits the use of scrapers in the Zetec engines. But allows any stock pan or windage tray -- this is just silly. The stock Zetec trays have scraper louvers in them -- and the Zetec E sump has them as well as advanced piston bay segregation baffles -- ala F1. Oh well.

Porsche tried adding oil squirters to the 928 wetsump engine and had to withdraw them because of the extra oil in the windage cloud as with your engine builder's experience. If you can quickly extract the oil after it has performed its cooling duties they are an advantage. For engines sitting on the edge windage-wise, like the 928, they could be a problem.

To give an example of how deleterious windage losses alone can be, the Nissan SR20 and KA24e/de are interesting. The mere presence of the girdle in both these engines causes a 5% power loss. Source: NISMO.
[Edit: I just finished some windage control parts for the QR25. This is when it gets really interesting at least for a nutter like me ;-) -- you can see the influence of previous engine designs and how they try to work through design problems, in this case the heritage from the SR20 is very clear.]

Scrapers and dry sumps generally have no effect on the radial and tangential spray patterns other than to let them revert closer to their ideal. In fact they increase oiling to the bores at least orthogonally to the crank axis because they both help disrupt the pressure differential that would draw oil into it rather than let it fly away. This happens in the upper two quadrants (roughly) whereas scrapers and dry sumps scavenge ports are typically present in the lower two quadrants.

There are some nice piston oilers in the NA 2.0 Porsche 924 rods. People that have mis-installed their bearing shells and blocked these holes report the rapid destruction of the engines from heat.

If your engine is tuned to take advantage of the additional heat transfer a net gain can result. I just had to convince a customer in NZ to leave in the piston squirters in his Honda B18C5 and I am normally all about reducing windage losses.

In the case of the Honda and a number of other engines, I think NVH is secondary to longevity since otherwise comparable engines in their lineup lack the squirters. F22 versus H23, etc.

[Guy Croft]

Kevin, hi

re:

Scrapers and dry sumps generally have no effect on the radial and tangential spray patterns other than to let them revert closer to their ideal. In fact they increase oiling to the bores at least orthogonally to the crank axis because they both help disrupt the pressure differential that would draw oil into it rather than let it fly away. This happens in the upper two quadrants (roughly) whereas scrapers and dry sumps scavenge ports are typically present in the lower two quadrants.

Could you please describe this more simply? You inhabit this world so I am sure you know what you are talking about and I think I understand what you mean, but many will have no idea at all, thanks.

Interestingly, on the subject of windage losses (basically aerodynamic drag from crankcase gas/oil) in the crankcase, I heard (from a retired F1 engine designer) that a lot of effort - well, to be frank - a lot more effort - is now put into 'cleaning up' the inside of the crankcase and other internals to reduce windage. I imagine - though I don't know for sure - that this is to reduce turbulence, eddies, vortices et alia generated by the media around sharp corners. If they're doing it in F1, you can be sure there is a reason. Mind you, for most folks that kind of internal radiusing and polishing is very time consuming. I did actually polish the inside of a TC unit once, took weeks.

In the 'old days' (readers of the late 'Car and Car Conversions' magazine will know what I mean - I grew up on it!) it was commonly said that polishing internally 'improved drain-down', ie: the recovery of oil droplets/liquid back to where it belongs - the sump. Whether anyone realised the added influence on windage (reduced losses) at that time (20 plus years ago) I don't know. I guess some did.

It might be worth my mentioning some frictional characteristics relating to engine losses. These figures are typically cited in the more advanced books. As % of power loss :

pistons 25%
rings 19%
crank 12.5%
rods 10%
oil, water pumps and ancillary drives 22.5%
valve train 6%
windage 5%
The contribution of the crank seals alone can account for as much as 20% of the overall crank friction.

The astute reader will be able to grasp readily the reason for citing these basic things. A powerful race engine will be the result of the sum of the parts, no one thing will bring anything like that end result on its own, however easy it may be to fit/do.

GC





GC

[sumplug]

There is a firm yes or no about using 'knife edged' cranks. I am a firm believer in them. Some say they do not work. What do you guys think?
Also, balancing the whole bottom end as one unit to zero, makes power and reduces pressures, as does knife edging!.

Andy.

[Guy Croft]

Yes, knife edging.

Well, we can, of course, engage a top firm like Arrows to make a steel billet race crank for us, should we need to, and of course some engines need them. The TC 2liter Fiat, for example, absolutely does not need one, it already has an En40B forged one. A crank of unsurpassed provenance. And if Arrows do the crank they will doubtless ask if the feature of knife-edging (aerodynamic shaping of webs and counterweights) is called for. This is usual.

But for clubman tuning, which, in all conscience is what this site is about, there is an absolute scale of importance for tuning mods that willl put cost v benefit things first. On a scale of 1-100 things to do to make an engine powerful and reliable, the knife-edged crank is firmly in the 90-100 region. I am so deeply involved in costings ever day that I can tell you, that whether this is boring or generalised, it's true and my methodology for tuning is well-defined and much copied. It puts the budget (which is never enough) precisely where it belongs and I have not yet had the phone call from a prospective client, however well informed, that has not led to his part or full re-appraisal of how the engine build should be 'properly' undertaken.

Balancing is totally another matter and belongs in the critical 1-10 bracket. Or is actually number one if the flywheel has been machined/modified in any way or swapped. failure to expedite this op can be life-threatening. You all know that I have done more TC engine prep than most will do in a lifetime, but I have never undertaken knife-edging. Lightening of counterweights, yes, but knife edging, no. Mainly I think because injudicious removal can easily make the crank unbalanceable & thus scrap, and for me, as a professional race engine builder, if that risk exists, it is definitely not 'cost-effective' to undertake.
What the private individual does is his own affair, if you all the time you want and spare parts handy, cool, but I will not recommend it as a tuning option at all here.

GC

[Kevin Johnson]

I will jump in here before responding to the previous post. David Vizard did some careful dyno testing of aerodynamically altered and lipophobically coated (oil shedding) cranks provided to him by Scat; coatings by Calico. I think you could probably safely do a rounding or chiseling of the leading edge of the counterweights without throwing off the balance to the extent that Mallory metal is needed for Clubman tuning. I do not have a Fiat crank sitting in front of me as I write this so I could not say if that profiling is already present (there are a couple out in the shop, though).

http://www.circletrack.com/techarticles ... index.html

I mention this specifically because I have run into at least two meanings of the term knife-edging. Some mean taking material off the sides of the counterweights -- a much more involved process -- and some mean modifying the leading swept surface.

Probably still in the 90-100 region.

Yes, knife edging.

Well, we can, of course, engage a top firm like Arrows to make a steel billet race crank for us, should we need to, and of course some engines need them. The TC 2liter Fiat, for example, absolutely does not need one, it already has an En40B forged one. A crank of unsurpassed provenance. And if Arrows do the crank they will doubtless ask if the feature of knife-edging (aerodynamic shaping of webs and counterweights) is called for. This is usual.

But for clubman tuning, which, in all conscience is what this site is about, there is an absolute scale of importance for tuning mods that willl put cost v benefit things first. On a scale of 1-100 things to do to make an engine powerful and reliable, the knife-edged crank is firmly in the 90-100 region. I am so deeply involved in costings ever day that I can tell you, that whether this is boring or generalised, it's true and my methodology for tuning is well-defined and much copied. It puts the budget (which is never enough) precisely where it belongs and I have not yet had the phone call from a prospective client, however well informed, that has not led to his part or full re-appraisal of how the engine build should be 'properly' undertaken.

Balancing is totally another matter and belongs in the critical 1-10 bracket. Or is actually number one if the flywheel has been machined/modified in any way or swapped. failure to expedite this op can be life-threatening. You all know that I have done more TC engine prep than most will do in a lifetime, but I have never undertaken knife-edging. Lightening of counterweights, yes, but knife edging, no. Mainly I think because injudicious removal can easily make the crank unbalanceable & thus scrap, and for me, as a professional race engine builder, if that risk exists, it is definitely not 'cost-effective' to undertake.
What the private individual does is his own affair, if you all the time you want and spare parts handy, cool, but I will not recommend it as a tuning option at all here.

GC

[Kevin Johnson]

Kevin, hi

re:

Scrapers and dry sumps generally have no effect on the radial and tangential spray patterns other than to let them revert closer to their ideal. In fact they increase oiling to the bores at least orthogonally to the crank axis because they both help disrupt the pressure differential that would draw oil into it rather than let it fly away. This happens in the upper two quadrants (roughly) whereas scrapers and dry sumps scavenge ports are typically present in the lower two quadrants.

Could you please describe this more simply? You inhabit this world so I am sure you know what you are talking about and I think I understand what you mean, but many will have no idea at all, thanks.

In a straight four like the Fiat the principal pumping action is between cylinder pairs 1-2 and 3-4. This gives a lateral or sideways component to the whirling tornado of air around the crank. So most oil caught in the cloud will be whirling around and back and forth about the long axis of the crank. This suction will draw in much oil right as it leaves the bearings -- certainly from the mains and from the rods as they sweep through about 270 degrees of their path. This force is orders greater than gravity. However, gravity still perturbs the equilibrium of the system and so the bulk of ejected oil from the system will be downwards towards the sump.

A scraper operates in different ways at varying rpms. At high rpms it helps to disrupt the pressure differential holding the oil around the crank. More oil will be thrown to the sump floor or shunted by the scraper blade but because of the weakening of the entrainment of the oil, proportionately more will be released in the region plus or minus top dead center, i.e. into the pistons and cylinders. So, a net oiling increase.

The action of a dry sump -- that is to say a dry sump with suitable restricted venting so as to create a depression -- is even more direct acting. The reduced atmosphere reduces the pressure differential; a simile might be a dust devil versus an F3 tornado. More oil is free to follow its normal path of radially -- like spokes on a wheel -- and tangentially -- like dirt flying from the tread of that same wheel. These paths collectively describe discs in three-space that are perpendicular to the crankshaft lengthwise.

The underside of the piston and part of the cylinder bores are exposed to these discs -- a more concentrated bath of oil. Since the thrust face of the cylinder bore receives even more -- being in the handed path of rotation -- that is a bonus. But the sides of the cylinders receive less so that is a negative and this is the area that provides "scraped oil" for the wrist pins. A squirter shooting straight up the beam or a passage drilled along through the beam provide direct oiling to the interior portion of the wrist pin 100% of the time.

Most higher end dry sumps include a scraper to direct oil to the scavenge ports. The Formula Ford ARE sump I have sitting here has this as well the TRD Toyota Atlantic pan I am working on.

Interestingly, on the subject of windage losses (basically aerodynamic drag from crankcase gas/oil) in the crankcase, I heard (from a retired F1 engine designer) that a lot of effort - well, to be frank - a lot more effort - is now put into 'cleaning up' the inside of the crankcase and other internals to reduce windage. I imagine - though I don't know for sure - that this is to reduce turbulence, eddies, vortices et alia generated by the media around sharp corners. If they're doing it in F1, you can be sure there is a reason. Mind you, for most folks that kind of internal radiusing and polishing is very time consuming. I did actually polish the inside of a TC unit once, took weeks.

Another area of windage research is in high speed computer disk drives. In F1 the grip of the chassis is hugely important. Under 2 or more Gs of lateral acceleration oil is moving sideways and so compartmentalization reduces incidental losses from adjacent bays. Used in Winston Cup too.

In the 'old days' (readers of the late 'Car and Car Conversions' magazine will know what I mean - I grew up on it!) it was commonly said that polishing internally 'improved drain-down', ie: the recovery of oil droplets/liquid back to where it belongs - the sump. Whether anyone realised the added influence on windage (reduced losses) at that time (20 plus years ago) I don't know. I guess some did.

I am certain that some did. Directional screening predates that. You could probably find more evidence by looking at advanced motorcycle engines. The straight six built by Honda back in the 60s was certainly F1 level.

It might be worth my mentioning some frictional characteristics relating to engine losses. These figures are typically cited in the more advanced books. As % of power loss :

pistons 25%
rings 19%
crank 12.5%
rods 10%
oil, water pumps and ancillary drives 22.5%
valve train 6%
windage 5%
The contribution of the crank seals alone can account for as much as 20% of the overall crank friction.

The astute reader will be able to grasp readily the reason for citing these basic things. A powerful race engine will be the result of the sum of the parts, no one thing will bring anything like that end result on its own, however easy it may be to fit/do.

GC

I think the windage percentages would rise markedly for an engine in motion. At present the technology does not exist to accurately model changing velocity vectors for a physical engine mounted to a dyno (tilting isn't enough) -- same idea as F1 losses from oil flying sideways. The figure I heard kicked around for F1 was 8%.

Also, there are different sorts of dynos in use. A steady state dyno will not show the improvements that reduced mass will allow in acceleration like an inertial dyno can. Windage is highly complex in the technical meaning of complex.