Oil Control In Rb's For Circuit Drag Or Drift

[bubba]

GT-RZ, from what you are saying (having a higher pressure in the head than block), would blocking the cam cover breathers completely and only venting the block to atmosphere achieve that?

[Adriano]

An interesting read on this topic, that generates -10psi crankcase vacuum can be found here

http://www.v-eight.com/tech_forum/viewtopi...amp;t=238"]undefined[/url]

[GT-RZ]

GT-RZ, from what you are saying (having a higher pressure in the head than block), would blocking the cam cover breathers completely and only venting the block to atmosphere achieve that?

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.

[Beer Baron]

just to add some fuel to this fire. m speed. well known japanese circuit racing competitor. they are among the fastest ever cars to compete in the tsukuba time attack events running in the 54second bracket. they run a wet sump... they have no sump extension (but I believe they run a swinging pickup). and they do run a drain from the rear of the head BUT to my eyes it's pointing towards the intake side of the engine. any comments? they certainly haven't had any problems i've seen, not breathing any oil or blowing any motors.

[GT-RZ]

An interesting read on this topic, that generates -10psi crankcase vacuum can be found here

http://www.v-eight.com/tech_forum/viewtopi...amp;t=238"]undefined[/url]

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.

[GT-RZ]

just to add some fuel to this fire. m speed. well known japanese circuit racing competitor. they are among the fastest ever cars to compete in the tsukuba time attack events running in the 54second bracket. they run a wet sump... they have no sump extension (but I believe they run a swinging pickup). and they do run a drain from the rear of the head BUT to my eyes it's pointing towards the intake side of the engine. any comments? they certainly haven't had any problems i've seen, not breathing any oil or blowing any motors.

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

Edited July 2, 2009 by GT-RZ

[Adriano]

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.

There is no pump in the setup, only a venturi in the exhaust. Im running a true venturi in the intake, which should generate a fair vacuum. I think you are emphasising the oil pump creating a -ve pressure in the sump too much, as the volume of oil pumped relative to the volume of blowby makes it insignificant. By increasing the vacuum in the crankcase, ring sealing is actually improved, and parasitic losses by windage and piston pumping losses are reduced significantly. although oil pressure relative to atmasphere is reduced, The real oil pressure differential between the oil galleries and the crankcase(which is what really matters) is improves or remains constant. Most vacuum pump setups run about 10psi vacuum.

[Roy]

Serious question, why dont std Rb20s have the problems of the RB26s etc? I mean, i run 19psi, and its run 21-22psi over days at Dutton Rallies. It gets rev'd out to around 8,200-8,500rpm in 2nd gear, 3rd and up i shift at about 7,800. And it makes 260rwkws at 18-19psi, who knows what it is making at the higher boost?

I would think that the boost levels and revs and reasonable amount of power would mean i should see the usual RB breathing problems, but none of the similarly powered RB20s doing track work breath. I mean my catch can is dry of oil. I did ths years Dutton on an RB20 that run 1.55bar for 3 days and didnt breath a drop of oil

So what is different about the RB20, perhaps the difference can translate to other RBs?????

[GT-RZ]

There is no pump in the setup, only a venturi in the exhaust. Im running a true venturi in the intake, which should generate a fair vacuum. I think you are emphasising the oil pump creating a -ve pressure in the sump too much, as the volume of oil pumped relative to the volume of blowby makes it insignificant. By increasing the vacuum in the crankcase, ring sealing is actually improved, and parasitic losses by windage and piston pumping losses are reduced significantly. although oil pressure relative to atmasphere is reduced, The real oil pressure differential between the oil galleries and the crankcase(which is what really matters) is improves or remains constant. Most vacuum pump setups run about 10psi vacuum.

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!

Edited July 2, 2009 by GT-RZ

[Adriano]

The piston rings are expanded by the difference between the combustion pressure and the crankcase pressure. by giving it vacuum, the rings expand harder against the walls, and blowby is reduced.

I agree with the point of the pressure(or neg pressure as the point may be)on the bottom of the piston, but the pumping losses are assaciated with moving the gas under the piston back and forth as the piston moves. Reduced pressure reduced the mass of the gas. After reading this thread, i will be hooking my catchcan setup to a baffled breather in the block

Edited July 2, 2009 by Adriano

[robots]

Interesting to see how it turns out eventually. As TROY said, whats wrong with those rb20s ? They just shit on any other rb in terms of live cycle stock vs stock. I took my pretty stock rb20(rb25 turbo) stock ecu everything to the track. No oil catch can etc. Oil cooler and a bit overfill. I was out there for the whole day, revving it. The lowest oil pressure under braking I got was 1.5bar. It didn't use any oil at that time nor run any bearings or any usual rb-failures. RB25s on the other hand.

[Beer Baron]

I reckon if when the engine is apart you enlarge the internal oil returns, and put a smaller restrictor in the oil feed to the head then the battle is nearly won.

apart from that the common sense stuff of baffled/enlarged or both for the sump and sensible oil catch tank arrangement and it should live a happy life.

[joeyjoejoejuniorshabadoo]

you mean with the stock returns?

[NXTIME]

I reckon if when the engine is apart you enlarge the internal oil returns, and put a smaller restrictor in the oil feed to the head then the battle is nearly won.

apart from that the common sense stuff of baffled/enlarged or both for the sump and sensible oil catch tank arrangement and it should live a happy life.

My old Japan-spec drag engine had this done (enlarged oil returns, de-burred block, and enlarged sump) and didnt breathe a drop. No rear oil drain/breather in sight. However, it was built a few years ago (c. 2003). Having said this, we added an oil restrictor and a rear oil drain/breather (going to the the inlet side of the sump) anyway when it was rebuilt.

[Swiper the Fox]

just to add some fuel to this fire. m speed. well known japanese circuit racing competitor. they are among the fastest ever cars to compete in the tsukuba time attack events running in the 54second bracket. they run a wet sump... they have no sump extension (but I believe they run a swinging pickup). and they do run a crankcase vent to the rear of the head and to my eyes it's pointing towards the intake side of the engine so looks like they have it set-up correctly. any comments? they certainly haven't had any problems i've seen, not breathing any oil or blowing any motors.

fixed

Edited July 2, 2009 by DiRTgarage

[Beer Baron]

yeah it could well be a vent. it's certainly not as low in the head as it could be, and it does semm to have another small fitting on there (for a pressure/vacuum gauge perhaps?).

[Beer Baron]

My old Japan-spec drag engine had this done (enlarged oil returns, de-burred block, and enlarged sump) and didnt breathe a drop. No rear oil drain/breather in sight. However, it was built a few years ago (c. 2003). Having said this, we added an oil restrictor and a rear oil drain/breather (going to the the inlet side of the sump) anyway when it was rebuilt.

yep this is what the guys who built my current N1 nur based engine did. deburr block, enlarge/port internal oil returns, oil restrictor in head oil feed, and recommended running a trust sump extension and extended pickup which I am. also fitted mines cam cover baffles and run a 3 litre catch tank with 22mm hose to it, vented to atmosphere. hopefully it will work well enough for it's expected 350 or so awkw and circuit use. they have built tons and tons of RB26s so I trusted their recommendations.

[Swiper the Fox]

yeah it could well be a vent. it's certainly not as low in the head as it could be, and it does semm to have another small fitting on there (for a pressure/vacuum gauge perhaps?).

BB see those large galleries in the rear of the head near the head bolt holes...do you think oil would prefer to drain through these to the sump...or through a tiny little hole through a fitting mounted higher up in the head. ?

Thanks for digging up the pic. A picture tells a 1000 words.

[GT-RZ]

The piston rings are expanded by the difference between the combustion pressure and the crankcase pressure. by giving it vacuum, the rings expand harder against the walls, and blowby is reduced.

I agree with the point of the pressure(or neg pressure as the point may be)on the bottom of the piston, but the pumping losses are assaciated with moving the gas under the piston back and forth as the piston moves. Reduced pressure reduced the mass of the gas. After reading this thread, i will be hooking my catchcan setup to a baffled breather in the block

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.

Edited July 2, 2009 by GT-RZ

[Swiper the Fox]

all the big Jap set-up's ive seen vent the block on the RHS.