GT-RZ

Well you may not be too far from the truth in one respect... I have not checked but how big are the standard oil drains in the 20 compared to the 26? Generally enlarging the returns in 26's would probably prove enough relief, the extra line from the rear of the head just provides an additional channel. If the RB20 has the same size returns as the 26 then it is clearly better setup to allow movement of oil/gas around the engine since the RB20 has smaller cylinders which in a volume sense given the combustion volume would produce less blow-by if both engines were fed the same boost and had equal wear... Most of the later discussion was to do with blow-by which really only affects higher performance engines (or not if badly worn out) as they deal with more boost but it would not hurt to be set up for the worst? low pressure or low vacuum in the crankcase is clearly beneficial to everyone. If it's needed or not given the particular setup is a different case.

8-10inHG is about 5psi They only recommend more vacuum pressure in high RPM situations where obviously more blow-by is being created. Which leads me to believe they are talking about the actual 'suction' of there vacuum system not the atmospheric vacuum pressure in the crankcase. Because if you could maintain the same atmospheric vacuum regardless of RPM then there would be no need to increase the atmospheric vacuum. However given that they only have one point of 'suction' the faster the rate positive pressures climb within the crankcase then the faster they will have to 'suck' it out. So 5psi of vacuum that the machine is pulling with would mean allot less than 5psi atmospheric vacuum within the block at that time depending on the blow-by load. The patent i read and posted earlier recommoneded around -0.15psi of atmospheric pressure within the crankcase, i assume you would measure this with a seperate gauge attached to the block somewhere, which this system lists in there patent. How much vacuum the 'device' must create to achieve this is not our problem. The only advantage a LOW vacuum could have for rings that i can see is rather a reduction of pressure on the lower rings due to little or no atmospheric mass interfering with the piston rings (pushing against them) on the downward stroke, which we've talked about earlier just not directed to rings. But like my example above (my last post) if you start to create high negative pressures then you replace the positve force on the rings with a negative force and have the same problem as before. I would not say that vacuum is good for the rings but rather low resistance is good for rings which would be sufficient at zero pressure / very low vacuum I'm glad to see the article documents issues with oil feeds under stronger vacuum, that was a given. It is also a given that if you want for some desirable reason 'high' vacuum' in your crankcase you will have to upgrade ALL of your seals to something stronger because vacuum is the opposite to boost!! Previously your problem may have been oil trying to bust it's way out of seals, now the problem is air trying to bust your seals from the other side. I think this is all very straight forward. there is no special power behind a vacuum. If you have positive pressure of 20psi in the crankcase @ 5000rpm before and you introduce a vacuum that keeps the pressure at a steady rate of 0psi @ 5000rpm then you have a 20psi drop in pressure which everything will benefit from. If you increae the negative pressure to -20psi then you just went and welcomed some old problems back in plus some new ones. Because vacuum and boost are equal and opposite. they put the same FORCE on an object. Id like to mention that the ONLY benefit a really high vacuum could have would be un-noticeable change in atmospheric mass in the crankcase which could help an un-noticeable amount with the rotation of the crank (which is why the shape of a crank can be important, the more aerodynamic it is the less you worry about this) But anything at zero atmospheric pressure or slightly lower is more than enough and any gains are to be made by removing the Positive pressure. As soon as you introduce higher vacuum pressures you add the problems with negative forces acting badly on the pistons/rings and oil/seals etc etc. Plus yea id love a dry sump as they already use a vacuum and have plenty of advantages in the first place but too much $$$ that i'm willing to spend.

I'm sorry to drag this off topic but saying -15psi is the same as zero atmoshpheric pressure is completely wrong. ok i'll start with the basics. Negative pressure (vacuum) and positive pressure (boost or blow-by in this example) produce the same FORCE. The only difference is that that operate in different directions. In saying that zero pressure is the same as -15psi is like saying 15psi is the same as zero pressure. it is not. My previous posts were my best effort to keep things in to a simple perspective and allow things to be understood easier for lots of reasons. first of all were you under the impression that zero pressure or absolute pressure as it should be reffered to means there is Zero mass within the crankcase? i tend to think so from your comment and you have been mislead. vacuum is measured in air molecules per cc and the higher the vacuum the lower the count there is no absolute vacuum on this planet that contains absolute zero mass. psi is simply used for a blind rounded figure for comparsion when dealing with vacuums. Back to the pistons that go up and down. you have already explained that you understand when a piston comes down from combustion it must fight the resistance of positive pressure (a force that is pushing against the underside of the piston). So with that understanding it must be clear that given a vacuum in the crankcase when a piston rises it must fight the resistance of vacuum (a force that is pulling on the underside of the piston) So given that you do not like high pressures within a crankcase you should also not want high vacuumes either. Think about this for a second... Zero pressure or as close to possible would be the ideal then wouldn't it... because then we have a 'neutral' zone where we have neither push nor pull on the pistons from extra mass and a minimal amount of mass for the rotating assembly to dance in. Also to think that a high vacuum pressures would not have there own problems is nieve. vacuum on earth unlike space, on this planet has a source of 'suction' in our example it can be thought of as a pipe out the block. Considering high vacuum pressure is pulling towards this one point then surely you can clearly see the implications with oil pressure/seals. In response to your earlier post regarding ring seals. as you will know rings are fitted with a tolerance, that is too allow for heat and expansion etc etc the specifications are provided as the result of extensive testing. a ring is simply a seal designed to compress mass and create pressure. having a negative pressure on one side and a positive pressure on the other side will not force the rings to seal better! In an exaggerated example lets say a ring had a failing pressure of 200psi and our combustion produced around 160psi and we increased the vacuum in the crakcase (which for this example will be measured with psi) to say 40psi. the ring now has 160psi pushing down and a further 40psi of vacuum pulling it, we now have a failed ring. To think that negative vacuum pressure from the crankcase would do something special that the positive pressure from combustion did not (like seal a ring better), seems illogical as BOTH FORCES act in the SAME DIRECTION. however if you have some information regarding your statement i'm interested to read it. i'm not sure what you are trying to say about n/a and combustion. it has nothing to do with this topic. nor is it true. a slight vacuum is used inside the crankcase to remove resistance which aids in making HP due to lots of reasons including reliability. a vacuum is created inside the cylinder when a piston moves down the cylinder, the greater the vacuum the larger the volume of air needed to fill the pressure gap and the bigger the bang. Forced induction just relies mainly on the opposite and shoves more mass in there to increase the pressure and the bigger the bang. plus vacuum pumps or vents to atmo are mainly needed in turbo or supercharged applications only because generally there is a larger tolerance in the rings and pressure being forced in the cylinder rather than only 'sucked' which results in more excess gas (blow-by). Never known of a vac pump used in the crankcase to 'pull' in more air through the rings... is this what your suggesting?

Well i'll take your word for it with the rings, but don't forget the rings will not be expanding much and where one gap is filled another is made. If i was to have standard atmospheric pressure inside the crankcase @ 14.7psi then the piston on the way down must fight this positive mass (it must compress or move the mass to make room) however lets not forget that as one piston moves down another one goes up so we have a balance with gasses jumping from cylinder to cylinder. All the while the crank and moving components also must deal with the same positive pressure. Now if i remove the atmospheric pressure down to zero. we have hopefully zero atmospheric mass to fight against when the piston moves up and neither does the rotating assembly. Now if i increase this vacuum to -15psi. when the piston moves upwards it must fight against -15psi once again we have created a situation where pressures switch between cylinders. As for the rings what you talk about may happen at some degree but if you increase the vacuum too much you simply increase the load on the piston rings and there seal will fail at some stage. i don't know when, not to be predicted. Then again unless it's perfection you seek then standard atmospheric pressure (vent to atmosphere) from the block would be sufficient? If you plan on leaving the vent through the head breathers i think it would be a good idea to install the rear hose to the head to allow pressures and oils an easier ride. Or you could just do both and never worry I still don't think the vent on either side of the block would matter as long as both sides are above oil level and remain parallel to the crank (make use of the venturi affect). They will do the same job. Equalise pressures and allow oil/air to move around easier. Anyone got a pic of the m speed engine yet? i would like to see where they plumbed the return in. as if they are using the crank the produce a venturi affect i believe it will be offset to the centre of the crank, lower than centre on the exhaust side and theoretically higher on the intake although that might not be practical.

My emphasis on the oil pickup as stated was only in a sealed system with no blow by as an example. I never realised it was utilising venturi effect i only looked at the first picture but that makes it all the better, some real examples of what i was trying to say. Lower pressure in the block reduces resistance that the oil has to deal with when returning as well as the cranks rotating mass and the pistons down stroke. Too large a negative vacuum would infact decrease piston ring seal, it would help 'suck' through air as it is compressed in the chamber above. The idea is no resistance. nothing more. Think about it, if you had a massive vacuum on the crankcase then sure the downstroke of the piston would be in heaven but the compressive cycle would have the opposite. pulling against vacuum is the same as pushing against a force. zero pressure or a tiny vacuum in the crankcase is the perfect situation as there is almost zero atmospheric mass to deal with. How you deal with removing this pressure is up to you there is a million ways to do it. direct from the block using a pump, ventrino effect or through the head with the same options. The block would be the best option imo but that does not say through the head would not work. bbl!

very nice pik. they simply appear to be venting from the block via the head rather than directly. would be intersting to see how the breathers are rigged up. would show if they use a vacuum or just outside atmospheric pressures to lower the block pressure. Given the way nissan does it the only restriction in return flow is the small channels from the head to the block (excluding the rear two) this would just add another channel like mentioned before. imo plumbing this in to either side will not change things too much. so long as they are both above oil level. looking at how nissan places its returns in the block. paralell to that of the crank. the vortex airflow from the crank indeed flows straight past the returns and most definently uses a 'ventrino' effect within the block to aid return. imo this would be exactly the same either side of the block providing they are located correctly etc look at the oil return from the turbo. It is slightly offset lower than the centre of the crank. this eliminates almost all airflow travelling horizontally causing any restriction only the airflow travelling down the side of the block would cause any kind of partial vacuum for this return. Food for thought, pics of that car would be nice

Very interesting read! thanks. i only skimmed through it but was that a crankcase pressure of -10psi? or was that what the pump was sucking out? if the crankcase pressure was -10psi that's allot of negative pressure though i think optimum would really be anything slightly under zero, the aim is to reduce resistance. too much neg pressure and you will create problems of the opposite nature!! ie, help blow-by escape and hinder oil flow due to stuffed oil pressure!!! The patent i read earlier did not give much away but it did say it recommends around -0.08 to -0.15psi!! which is a big difference if you consider the 'adopted' normal atmospheric pressure to be around 14.7psi. Which is what your crankcase pressure would be if you have a vent to atmospehere directly from the block. And most likely even higher without. I suppose a real solution would be a vacuum pump with a regulator to try and keep things in check.

What i was saying is ideally a negative pressure in the block is desired. If there was no blow by and no increase in heat then a completely sealed system would work. As the only extra pressure in the head would be that of displacement from the block as oil is removed from the sump. it would work in a continous cycle. I think if the cam cover breathers were blocked completely you may have a high build up of hot gas in the head which is why they were most likely placed there from nissan. It is important to remember that the higher the atmospheric pressure (within the block) the higher the atmospheric mass which when heated would in turn create higher pressures in the head. The vacuum is simply aimed to provide a relief in resistance for that of returning oil and also the crank and piston assembly. Too much vacuum and you could end up with oil pressure issues but that would be in an extreem circumstance i would think. Having a relief/vacuum directly from the block simply aids in removing the pressures directly from the source rather than making the head deal with return problems etc etc as a result from blow-bye raising pressures. The way nissan set it up from factory (re circ with BOV) sucks all excess pressure out the head and block which in turn achieves the same result but may be pushed to the limit under more extreem conditions (more blow-by, higher heat etc) as all the gas pressure can only be equalised by using the oil returns.

lol i didn't realise that badge was your only problem. i'n the silvia it hit the front belt cover. oh well that's an easy fix for you!!!

I was going to say. setting up to make your own cast engines is big $$$ i look forward to seeing this aluminium cast engine. would have to be very thick imo to deal with twisting stresses alone.

Gary i think the crank would create a partial vacuum but not an atmospheric vacuum more just a vortex of air possibly aiding in oils return to the sump once it's journey from the head is complete. I say this simply because given that the vortex air stream from the rotating crank does not extend to the head is simply churns around air within the block. I still think that the key solution would be to maintain a slightly negative pressure in the block or at least a noticeably difference in pressure in comparison to the head. and i don't think the perfect solution would be a vent to atmosphere (catch can or alike) although this would certanly lower pressures to the atmospheric pressure but a slightly negative pressure would be desired? When looking at the factory system i think you will notice something clever. the factory setup vents any excess gasses in to the intake which prevents any release and keeps emissions happy. It would also aid in creating a pressure drop. As obviously a slight 'venturi effect' would be created.(airflow rushing past sucks air from the breathers) this again makes the factory BOV especially important when running the factory re-circ setup. The only other way you could create this would be to plumb it in the exhaust, however emissions and heat problems would be much harder to overcome. A better way for race applications would be perhaps attach an external vent from the block (above oil level, intake side) to the intake with inline filters/seperators and probably quite importantly a one way valve (especially important when off the throttle with no BOV) To achieve the 'venturi' effect it is especially important to join the vent in the direction of the intakes airflow for obvious reasons. The only other way would be to go out and setup some sort of external vacuum pump attached directly to the block which would be better because that way any pressure drop would be instigated through the block and not the head, which would maintain a higher pressure in the head which imo is desired. As everyone knows any sort of slight vacuum would be very beneficial for the crank/pistons as there is less pressure restistance on every stroke/rotation, which would most likely lead to a slight power increase/response but certainly less stress on components. With that said i think it's safe to say the external drain/vent can do no harm and would infact help drainage in the right circumstances. And given that gary has a vent from his dipstick and dirt has a vent from the sump (which most likely will be above oil level when under load) and that they both vent to atmospheric presure they will be achieving minimal raising pressures in the block but almost certanly never achieving a vacuum. Obviously gary has shown neutral pressure via his vent coupled with an additonal drain/vent on the rear of the head prove sufficient. Dirt's setup seems to show maybe neutral pressure in the block alone is enough (for the circumstances hes tested in) adapting the vents to one of the 'vacuum' setups above would definently further increase positive results but it may not be neccissary. i Did some research and found a patent similar in ideas listed above which states: "Ideally, the pressure within the crankcase should be maintained at a low negative pressure level, as for example from between 1/16th to 1/6th psi, which equates to a vacuum level of approximately a negative 0.08 to a negative 0.15 psi." As for the argument of the rear 'hose' being a drain or a vent i think it's clear it is BOTH. depending on the relationship of RPM and blow-by of the engine

Post 448 has a picture of dirts engine and sump attachment. Any return from the head would be ideally placed above oil level which yours most likely will be when running, but imo placing it at the height of the factory turbo drains would be optimum.

I always was led to believe the heads in VL's cracked due to radiator placement and air getting trapped in the head causing hot spots...

looks like that due to the oil colour. maybe the gasket is fine and when the rebuild was done the head was slightly warped and not re faced?? Generally i think most alu heads need a skim. maybe if you know details of the build?

noooo save the head! hah. it's a shame we could not get hold of nissan engineers reports. would have been tested in all kinds of situations!

the blow by is additional pressure though. If you were to fill up a tank of water and suck some water out through a hose the resulting pressure inside the tank would get lower. And if you were to do the reverse and add water the pressure would increase. If you were to punch a big hole in the top of the tank (breather) and suck water out (oil collector in sump) the lower pressure inside the tank (block) would be balanced as the higher atmospheric pressure rushes in from outside the tank (head). In an engine when oil is sucked up from the sump there would be a pressure drop, however almost simultaniously in an engine the negative pressure would be equalised from air/oil from above. this reaction would literally be sucking air/oil back in to the sump. Blow-by simply reduces any pressure decrease produced by the oil being sucked out and would lower the return pressure. making the whole process less efficient. Given that, the pressure in the head would always be slighly higher than below due to oil constantly displacing air (displaced air escapes out the breathers). unless there is some severe blow-by. also the return pipe on the rear of the head may not necissarily act as a drain only for oil that's why i said oil/air. it simply allows faster flow, be it air or oil as pressures are attempting to equalise.

So really the only difference between your views is which side to have the return on. I'v been thinking though... Forget about excess gasses getting through the rings for a second and pretend they are sealed perfectly, for now. you have the block/sump and the head which are only connected by channels. When oil is 'sucked' up the intake from the sump it creates a pressure drop in the block/sump and simultaneously as the oil arrives in the head there is a pressure increase in the head. If there was no blow-bye or escape route via vents in the head this would leave a very nice system as the lower pressure from below would work together with the raising pressure in the head and force air/oil down the drains in attempt to equalize the pressure. Now if the drains were inadequate the solution would be to add more drains or enlarge existing ones. But the problem with preventing this perfect system is obviously blow-bye. That is, rings allowing some gasses to escape past them in to the block. This in turn however slowly would raise pressure in the block which must be released to keep the lowest pressure in the block, so Nissan carefully placed vents coupled with a divider to minimize oil escape and allow the excess pressure to escape. Unfortunately the downside to this is that we loose almost all our pressure increase in the head leaving only the lower pressure from below aiding transport of the oil/air back down below. However another downside is that as blow-bye/rpm increases the pressure in the block will be rising resulting in oil/air returning at a slower rate. Given this then we do not want a ven't on the block/sump (unless this vent is actually creating its own pressure drop which atmospheric pressure will not be sufficient) as this will only help neutralise any pressure drop that is naturally occuring. The only way to add any extra vent would be in the head which does not do much for the block/heads oil/air return channels flow, that is again as the rpm increases the stronger blow-bye and the smaller the pressure drop in the block/sump resulting in less 'suction' on the oil/air in the head. So if we deemed enlarging existing oil/air returns inadequate there is a need for another escape for the oil/air. This could be achieved by adding an external return from the head (must return above oil level). It simply allows an extra route for oil/air to return through as with the natural pressure drop geting weaker with higher RPM due to more blow-bye the oil/air relies less and less on partial vacuum and more on gravity, hence the larger surface area it can return through the better. Going from that then the vent/return could be placed anywhere but the rear of the head seems logical as thats where the largest returns are from the factory given that under forward acceleration oil will flow in that direction. (unless we can have some physics to back up oil going forwards at 70* angles) Hope that made sense i tried my best to get my thoughts across. This does not mean a sump drain could not be used that connects directly from atmospheric pressure to the block providing the drain is submerged under oil which is far denser than air and should not cause any problems. like dirts: In short what needs to be achieved is lower pressure in the block and higher pressure in the head with adequate returns to allow the higher pressure in the head to continuously attempt to equalize that in the block whilst moving sufficient oil down low. which is not a problem until we take in to account blow-bye. The less of that the less problems full stop. what's these no-gap rings someone mentioned??

or go to U-pull it and rip out an RB30e check it out and if no good pull another out and pay 80bucks for a block like i'v done twice now. sleeve it if you want but probably no need when you can just refresh the bores in the usual manners. build it as strong as you like. perfect square ratio. drag racing then you could have it grout filled or leave it be and enjoy the extra torque. i don't see the big deal with harmonics, only as good as your balance and balancer. then the only issue is how strong your rods are. as obviously the longer the stroke the higher the piston speed at the same RPM. Not really an issue with forged rods. anyway sorry i'v drifted OT again

I agree in that it's the same engine no matter what forum. if it's going to be pushed you cannot ignore oil starvation in the bottom end. unless you like rebuilds. end of the day this is not supposed to be a heated debate but just a discussion on the best ways to deal with it. the more facts and real world examples the better. I can clearly understand garys point of view as it makes sense. excess oil in the head and accelerating forwards would require drains at the rear of the head (like factory) plus one more for extra drainage that plumbs in the exhaust side to make use of some vacuum pressure (like factory turbo drain does). makes sense even to the layman. Dirts side and the other 'unkown' engine builder mentioned obviously have strong beliefs in airflow through the oil returns as the root cause. according to 'unknown' the oil in the head under high acceleration acutally moves forwards against g-force and allows excess air pressure to escape up the rear 'vent'. this concept is not easy to understand but not necissarily untrue, so we will have to wait for dirt's air pressure findings or some other factual evidence that arises. To add to this we do have only one example; r33 racer who relieved his catch can oil overflow problem by using garys mod. has anyone used a block/sump vent to cure there issues? would be nice to compare.

of course. but the only reason for a billet block is to get massive HP. massive HP is only needed in drag racing and drag racing doesn't require water cooling because the whole thing is over in less than 8 seconds. you could get a billet block for circut but really a track car with too much HP to handle is not much good to anyone. you can only use as much power as you can put down.

i think RIPS are also interested in TB48's. have to see what happens. for my needs and 99% of us <1000hp is fine so we can live with humble RB30.

i'm confused. did you just answer your own question.

This is not an argument, simply a discussion. i like everyone else is just trying to see what's reasonable. I just can't get in to my head the whole air pressure thing stopping oil return when the dipstick stays put. maybe that could be better explained as so far there is no fact on that in this topic at all, only theory. What i can understand is small holes and lots of oil in the head and the more holes the easier it will return. maybe next time someone gets the chance to dyno a 900hp car? they could attach an air pressure gauge to the end of the breathers and in your case dirt block of your vent. see what the max reading is? although in the end it does not mater so much about the max power, more the horizontal forces acting on the oil coupled with maintained high RPM.

I hope we are not elaborating the problem. If we go back to basics we have an oil pump that is too efficient at pumping oil up to the head. the problem is obviously the return of the oil to the sump. Without modifying the oil pump we have to restrict the oil delivery and enlarge the oil returns. One of the oil returns originally suggested (sydneykid) was from the back of the head down to the exhaust side of the sump, using the 'vacuum' of the cranks pressure to theoretically 'suck' oil through the return pipe. The other suggestion was from (Dirtgarage) was to forget about another external return and instead have an additional vent from the intake side of the engine which theoretically would relieve any potential pressure in the sump on the basis that it would minimise airflow through the oil returns and allow oil to return without additional air resistance. So going by what has been said. Clearly the pressure inside the case is not evenly distributed because if that was the case the dipstick would be popping out given that this pressure is great enough to largely restrict return oil flow. so given that there is only one way to prove... tests. i suppose the proof is in the pudding. how many engines have you blown up sydneykid with your mods. how many engines have you blown up dirt with your mods? were they circut, drag? drift?

The above must hold some value? perhaps it's a good idea to run a vent from the sump and a return from the head plumbed to the exhaust side of the block??? best of both? what gary said does get me thinking though. as i remember my old worn CA18 used to pop the dipstick out, obviously relieving some pressure. and it certainly doesn't take much pressure to pop that out? does anyone have a video of the oil running forward in the head under acceleration? i would like to see this.