k80rum Posted January 28, 2008 Share Posted January 28, 2008 Can someone give me a quick sanity-check of my understanding regarding breathers in dry sump applications. People are asking for the camcover BB and I don't want to give duff information. From the searches I've done in the past, in a K-series application at least, the DS tank should always vent to a catch tank anyway. Opinion's divided on what's best for the camcover - you either a) have no breathers (running a sealed system) which advocates say have advantages and detractors say can put oil seals under more pressure. b) breathe the camcover to a catch tank (running the system at atmospheric pressure) which gives you an extra pipe run but no other downsides. It's down to personal choice, but if you want to play it safe and already have a camcover breather it's probably worth keeping one on the head (you don't need two on the camcover) Is that a fair summary Darren E K80RUM Website and Emerald maps library Superlight R #54 Edited by - k80rum on 28 Jan 2008 08:03:52 Link to comment Share on other sites More sharing options...
davef Posted January 28, 2008 Share Posted January 28, 2008 Mine is setup as a) - both breathers on the cam cover are sealed. b) would be incorrect - as the scavenge pump creates a partial vacuum within the crankcase, potentially unfiltered air would be flowing from the catch tank into the engine. Dave Link to comment Share on other sites More sharing options...
martinwhitcher Posted January 28, 2008 Share Posted January 28, 2008 Mine is as follows: cam cover is vented to pace oil tank which is in turn vented to the catch tank. as advised by Oily and Pace. Martin MW 51 CAT Superlight No.171 now known as:Superlight DVA 250 Link to comment Share on other sites More sharing options...
k80rum Posted January 28, 2008 Author Share Posted January 28, 2008 Thanks Dave & Martin Darren E K80RUM Website and Emerald maps library Superlight R #54 Link to comment Share on other sites More sharing options...
MartinWoodham Posted January 28, 2008 Share Posted January 28, 2008 Hi Darren, there's a;lso option c which is to vent the cam cover to the catch tank via a non-return valve. This prevents unfiltered air being sucked in via the breather, but allows excess blow-by gases to vent, if it gets so bad that the scavenge pump(s) can't cope. FWIW race cars tend to run sealed. Martin supersported ex-Roadsports B Link to comment Share on other sites More sharing options...
Casbar Posted January 28, 2008 Share Posted January 28, 2008 Mine as per Martin Whitcher, cam cover breathing to catch tank Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 28, 2008 Share Posted January 28, 2008 Davef, The concern about potentially unfiltered air in option b) is wrong (and a little bit paranoid). The net flow in the system is outward; breathing is the method by which piston blow-by gasses are expelled from the engine. Other than blow-by, a vented dry sump system just displaces air/oil from one cavity (the engine crankcase) to another (the dry sump tank) - the total volume remains the same and the only in-flow is the result of thermal effects on engine shutdown - you admit more "unfiltered air" than that when you remove the cap to check your oil level. Darren, The biggest concern with option a) stems from the scavenge pump becoming less effective as a vacuum is pulled in the crankcase. Pumps cannot suck in a vacuum. The gas pressure in the crankcase has to push the air/oil mix from the pickup to the scavenge pump. No pressure means no push. In the case of a sealed engine, piston blow-by becomes a significant factor which *helps* the scavenge pump. there's a;lso option c which is to vent the cam cover to the catch tank via a non-return valve. This prevents unfiltered air being sucked in via the breather, but allows excess blow-by gases to vent, if it gets so bad that the scavenge pump(s) can't cope. More paranoia, confusion and good old claptrap. Extra complication of a non-return valve which essentially means the engine is running sealed. "[Allowing] excess blow-by gases to vent, if it gets so bad that the scavenge pump(s) can't cope)"... a situation that occurs when your engine is already dead; if your scavenge pump can't cope, your engine is dead. If your blow-by is so massive your scavenge pump can't cope, your engine is dead. I'm going to take Martin Whitcher's description and change it subtly to emphasise the direction of flow of gasses: Pace oil tank is vented to both catch tank and cam cover. In the above setup there will be a significant, consistent flow from the oil tank to the cam cover (note direction). The flow to the catch tank will be equal to the volume of piston blow-by gasses. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 28, 2008 Share Posted January 28, 2008 If your oil tank only has one vent and the cam cover has two vents, you can use the cam cover as the junction point for the breather system... ... the oil tank vents to the cam cover ... the cam cover vents to a catch tank If you have only one vent on the cam cover, then you can use a tee-piece in the vent from the oil tank to the cam cover to expel blow-by volume via a catch tank. Link to comment Share on other sites More sharing options...
MartinWoodham Posted January 28, 2008 Share Posted January 28, 2008 Darren, FYI Peter's view is not the only one. Read around the subject and form your own opinion. Martin supersported ex-Roadsports B Link to comment Share on other sites More sharing options...
k80rum Posted January 28, 2008 Author Share Posted January 28, 2008 A big thanks once again to Peter, Martin and Casbar. Point take Martin. I think this is why discussions on the subject tend to run and run. Peter - What you say makes sense to me. It is how my system is currently set up: DS tank vent & camcover vent are connected, 2nd cam cover vent then leads to catch tank at atmospheric pressure. Since my DS tank only has one vent, and a replacement camcover would only have one vent, I had indeed wondered whether a T-piece between the two, to the catch tank would be a solution for me and it sounds like it will be. Subscribing to the train of thought that the direction of gasses pass from tank to camcover would mean that in the new T-piece setup, both catchtank and DS tank are being 'sucked from' in equal amounts by the crankcase vacuum, just as they are at the moment, BUT through half the area of hose as there's only one entry point to the camcover. Therefore the vacuum effect should increase very slightly. This could be mitigated by moving the T-piece as close to the camcover as possible. Darren E K80RUM Website and Emerald maps library Superlight R #54 Link to comment Share on other sites More sharing options...
Englishmaninwales Posted January 28, 2008 Share Posted January 28, 2008 Help!!!! I currently run CC's DS system on a 1400 forward facing supersport system and I simply left the cam cover vents as they were (front one to throttle body, rear to plenum chamber and the swirl tower vents to the catch tank). Seems to work ok,is this OK? Sorry for the hijack! Malcolm Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 28, 2008 Share Posted January 28, 2008 Subscribing to the train of thought that the direction of gasses pass from tank to camcover would mean that in the new T-piece setup, both catchtank and DS tank are being 'sucked from' in equal amounts by the crankcase vacuum, just as they are at the moment, BUT through half the area of hose as there's only one entry point to the camcover. The catch tank is *not* 'sucked from'. Both the crankcase and the catch tank are at lower pressure than the oil tank. The crankcase will not have a large vacuum. If, as it should be, the breather inlet to the cam cover has a large bore, the crankcase will be at or around atmospheric pressure. By definition, the blowby gasses need to be expelled, so there will be a pressure differential causing flow out to the catch tank. If the crankcase has a partial vacuum, there will always be an excess of pressure in the oil tank more than sufficient to make this up... ... "both catchtank and crankcase are being ''blown into' in equal amounts by the excess pressure in the DS tank" Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 28, 2008 Share Posted January 28, 2008 I currently run CC's DS system on a 1400 forward facing supersport system and I simply left the cam cover vents as they were (front one to throttle body, rear to plenum chamber and the swirl tower vents to the catch tank). Seems to work ok,is this OK? The throttle body vent is at atmospheric pressure. The plenum is at lower than atmospheric pressure (intake vacuum). The dry sump tank has a greater volume pumped into it (air and oil) than the volume pumped out of it (oil only). In your current set up, the only place that excess gas/air delivered to the dry sump tank can go is out of the catch tank. All of the gas/air pumped into the dry sump tank will exit via the catch tank. The gas volume in the engine needs to be replenished and it will do this by inhaling through the breather piped to the throttle body (atmospheric pressure). There will be very little flow at all through the breather to the plenum. Essentially what you have is a through draught of fresh, filtered air entering the engine at the cam cover front vent and exiting via the dry sump tank and catch tank. This arrangement tends to see a lot of oil vapour exit the catch tank. It can be a good idea to use this sort of arrangement for very highly tuned engines using Vandervell VP2 bearings which suffer from attack by acidic combustion by-products. You could... ... block off the vent to the plenum, as it does very little, if anything or ... ... re-route the dry sump tank vent back to the cam cover front vent ... block off the throttle body vent ... re-route the cam cover rear vent to the catch tank ... block off the plenum vent ... *but* be sure to drill out the cam cover vents to full diameter - one of them is a restrictor at the moment Link to comment Share on other sites More sharing options...
Englishmaninwales Posted January 28, 2008 Share Posted January 28, 2008 Thank you, Peter C I can confirm the extra venting from the catch tank. This is vented under the car and causes no problem. Im probably being dim, but is there really any need to change the setup? Is it causing harm or detracting from performance? Malcolm Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 28, 2008 Share Posted January 28, 2008 The only thing to watch for is excessive oil consumption. If you don't have issues with oil consumption, don't change a thing. Link to comment Share on other sites More sharing options...
Englishmaninwales Posted January 28, 2008 Share Posted January 28, 2008 Peter C Malcolm Link to comment Share on other sites More sharing options...
Nifty Posted January 28, 2008 Share Posted January 28, 2008 Confusion reins ❗ Why do CC set up the dry sumped cars with a "sealed" system if they could have a better system for the want of tuppence halfpenny of rubber pipe and a T piece. Mines a CC dry sump system with the usual two rubber blanking caps on the cam cover breather pipes. It's been working Ok. What vaccuum pressures are actually measured in the crankcase that might reduce scavenge pump performance dangerously. As the oil/air mixture is acting to pump air from the engine out through the catch tank, producing the said "vaccuum", then that means there is less air in the system to combine with the oil, and so it's a self regulating system surely Keep off the straight and narrow 😬 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 29, 2008 Share Posted January 29, 2008 and so it's a self regulating system surely You of course know that use of the word "surely" is a red rag to this bull... 😳 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 29, 2008 Share Posted January 29, 2008 It depends on whether you consider piston blow-by and seal leakage to be sound, calculated design elements for the critical matter of ensuring oil delivery. Caterham do it because a fair few people have got away with it over the years and it has become part of the body of knowledge formed from "that's how they do it in race cars". Good design allows a margin for unforeseen circumstances. Sealing a dry sump engine installation removes a degree of that margin. ... when I first ran my 250bhp engine on track, I ran it with closely controlled rev limits looking closely at all engine parameters on the datalogging. I started running it sealed. I also ran it with an Apollo tank to mitigate any oil delivery issues that might ensue. The datalogging showed a drop in oil pressure at sustained high revs. With no other changes, opening up a filtered breather in the head eliminated this oil delivery issue. There are other potential reasons why my engine may have been susceptible to marginal oil delivery. What I am certain I observed is that the use of a properly ventilated crank case removed a constraint on the oil delivery system, providing a greater margin of safety. Link to comment Share on other sites More sharing options...
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