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WTF is a catch Tank and do I need one ?


Hybrid_From_Hell
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OK

The 5.2 had a few bits i looked at and went :blink: what are they then ?

One I am told is a "Catch Tank"

About say 8" high 6 " wide and 4" deep, with a breather at least 1.5" bore on the top, and 2 maybe 5/8 BSP take offs

at the top end, the "Top Top" one is seperated form the one below it if you stare into the breather hole (on the top suface)

and then there is a drain hol on the base (bolt missing :lol:)

So, what is it, how does it get plumbed in, to where

and do I really need it ?

Can do pic if needed its in cleaning tnk drowing the dirt off at the mo :)

??

Nige

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I fitted a catch tank to my x-flow when I built my Westfield. There was a pipe from the crankcase which originally fed oil vapour back into the the carb inlet and therfore burnt off with the mixture. This crankcase breather was removed, replaced with a simple ally block and pipe, which fed into an oil catch tank fixed on the front bulk head. Mine was just a plastic catch tank, but you can get fancy shiny ally ones with drain tubes, I just used to empty mine when I had about 1/2" in the bottom.

Don't know if this helps Nige.

Jon

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Hi,

This is probably part of your ccv (crank case vent) system. It evacuates crank case pressure into the inlet system. Due to the oily nature of the gas it runs through a cyclone or swirl pot to seperate the oil from the air and so the air goes to the inlet system and the oil returns to the sump.

It should look conical in shape with the pointy end at the bottom. Gases from the crank case (cam cover) would enter at the side at the top to force the gases to swirl inside and the air escapes out of the top and the oil runs down the side and out of the bottom.

I've tried to find a picture, but couldn't.

Steve

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It's the bulk tank that catches all the petrol-diluted engine oil that your gutless old V8 blows out the crankcase breather due to being completely thrashed and knackered and having a gap between the pistons and the bores that you could fit your elbow down :P

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Simply put Nige it does exactly what Bogmonster said it does!

Bearing in mind the fact that you never rev the thing over 3 grand anyway you probably therefore don't need it!

Its needed on racers where you're constantly up at 7000rpm, but for a road motor is probably OTT. The idea is that it prevents your inlet system getting fouled with oil that comes through the breather system - you remove the bolt from the bottom from time to time and drain the oil out of it.l

Jon

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Simply put Nige it does exactly what Bogmonster said it does!

Bearing in mind the fact that you never rev the thing over 3 grand anyway you probably therefore don't need it!

Its needed on racers where you're constantly up at 7000rpm, but for a road motor is probably OTT. The idea is that it prevents your inlet system getting fouled with oil that comes through the breather system - you remove the bolt from the bottom from time to time and drain the oil out of it.l

Jon

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Hi Nige,

As said before by others it is just a crank case breather system mostly used for racing (compulsory for racing) and not really needed unless high power and higher revs and hard work are anticipated.

However, you building a 5.2 litre gazillion hp motor, you probably ARE going to work it a little? Looks nice to have a good catch tank that is baffled well so as not to spit out oil from it's breather and sexy braided pipes going into it, and it certainly won't hurt. Just remember to put a tap on the bottom of it so you can drain it easily.

Lara

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Given the current way Nige's build is going, let me correct that for you:

Looks nice to have a good money tank that is baffled well so as not to spit out money from it's breather and sexy braided more money going into it. Just remember to put a tap on the bottom of it so you can drain the money out easily.

Zim - the vacuum pump connected to it is about 5.3 litres :P

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Circulation is required on the rv8's hence me asking about the vacuum pump. As standard they go back into the air inlet which sucks.

Nige - speak to JE about what to do regarding engine breathers.

G

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...

Its needed on racers where you're constantly up at 7000rpm, but for a road motor is probably OTT. The idea is that it prevents your inlet system getting fouled with oil that comes through the breather system - you remove the bolt from the bottom from time to time and drain the oil out of it.l

Jon

I disagree, but then as far as engines go my interest is in the diesel camp - don't want no stinkin petrol guzzlers rolleyes.gif

The stock 300Tdi engine has one (of sorts) - I don't know what is used on other Land Rover diesels. Many low revving diesels use them - manufactures of long haul diesels have found that something much better than a typical cyclonic catch can is required to improve the life of turbochargers.

The cyclonic catch cans only separate largish oil droplets and let through large amounts of small (invisible to naked eye) oil droplets from the crankcase vapour. Mann+Hummel put in a lot of R&D for their ProVent device for this purpose.

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And where does one buy such a thing then Bushy?

Looks like a useful bit of kit for my old diesel 90!

Lara

I got my ProVent 200 in Aus. On the label it says made in Germany, so I would be surprised if you can't find suppliers closer to you.

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Just ordered one!!

I like the concept and they look well made!

Stops me needing to clean out inter-coolers and pipes! Great!

Diesels do tend to blow-by much more than petrol engines due to the high CR.

Thanks for the post everyone!

Lara

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With regard to the old cross flow mentioned above, Ford fitted several variations of "positive crankcase ventilation" depending on engine size and model year.

The larger engines fitted to later MKI and MKII Escorts used an oil seperator mounted on the back of the crankcase above the back end of the camshaft (which does throw oil into the seperator).

The seperator was designed to be cleaned every 2 years, it had internal baffling to remove the bigger drops of oil, the other end of it was connected to the inlet manifold via a non-return valve. This protects the crankcase in the event of a backfire.

The basic idea is that at part throttle the vacuum generated by the engine was greater than the pressure caused by piston ring blow-by so that the oil vapour and combustion by-products in the crancase could be burned by the engine to improve emissions (indirect emmisions I think was the phrase). A secondary benifit is that the crancase runs at partial vacuum which protects the oil seals when running at medium throttle/high speed such as cruising the motorway.

Air is drawn in through the filler cap which had a scrubber built into it, the air passed through the rocker box down the pushrod holes into the crankcase.

At wide open throttle it was possible on worn engines for piston blow-by to overcome the lower vacuum and the engine would begin to breath out, conversely a good "tight" engine would exhibit a powerful vacuum at the filler cap whilst idling.

The system employed by Rover was not quite as successful. There are several incarnations on PCV system but the later system employed a filtered inlet breather on one rocker cover and a "flame trap" breather on the other (opposite the oil filler which should be air-tight). The oil vapour is delivered by a T peice to both the plenum and the throttle body. Unfortunately this means that the crankcase is never under any significant vacuum, on a new engine the breather system by-passes the throttle plate and if broken it can affect idling.

Catch tanks are often fitted to allow the removal of the PCV system. Doing so will stop the oil vapour contaminating the inlet tract and fouling the valves. Whether or not the engine gets "thrashed" it will stay cleaner plus the fuel mixture is not effected by the contents of the crancase.

On systems where the PCV system is retained a catch tank will help to "filter" out the heavier oil perticles, better ones try to work like a Dyson vacuum cleaner. land rover's own TDi engine has a cyclonic oil seperator.

Thing is as observed they are only of limited effectiveness and similar success can be had using a flame trap, although these do suffer from blockages if not cleaned.

As for whether TDis breath more than V8s, it has very little to do with CR. The higher CR demands a "stronger" engine in any case. The piston ring blow-by is driven by combustion pressure.

The reason breathing is more noticeable on a diesel is the lack of inlet vacuum to consume it, TDis use the turbo inlet for this which serves to make the turbo quite filthy.

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With regard to the old cross flow mentioned above, Ford fitted several variations of "positive crankcase ventilation" depending on engine size and model year.

The larger engines fitted to later MKI and MKII Escorts used an oil separator mounted on the back of the crankcase above the back end of the camshaft (which does throw oil into the separator).

The separator was designed to be cleaned every 2 years, it had internal baffling to remove the bigger drops of oil, the other end of it was connected to the inlet manifold via a non-return valve. This protects the crankcase in the event of a backfire.

The basic idea is that at part throttle the vacuum generated by the engine was greater than the pressure caused by piston ring blow-by so that the oil vapour and combustion by-products in the crankcase could be burned by the engine to improve emissions (indirect emissions I think was the phrase). A secondary benefit is that the crankcase runs at partial vacuum which protects the oil seals when running at medium throttle/high speed such as cruising the motorway. Correct!

Air is drawn in through the filler cap which had a scrubber built into it, the air passed through the rocker box down the pushrod holes into the crankcase. You are contradicting the above correct statement here. The air goes the other way. The crank case does not and can not breath in! unassisted. (unless due to sudden cooling etc)

At wide open throttle it was possible on worn engines for piston blow-by to overcome the lower vacuum and the engine would begin to breath out, conversely a good "tight" engine would exhibit a powerful vacuum at the filler cap whilst idling.

Try it! And ask your self where would this "Vacuum" come from? That is why the PCV system was invented! All engines breath Out due to piston ring blow-by, Some more than others though

Or maybe I misunderstood what you were saying?

The system employed by Rover was not quite as successful. There are several incarnations on PCV system but the later system employed a filtered inlet breather on one rocker cover and a "flame trap" breather on the other (opposite the oil filler which should be air-tight). The oil vapour is delivered by a T piece to both the plenum and the throttle body. Unfortunately this means that the crankcase is never under any significant vacuum, on a new engine the breather system by-passes the throttle plate and if broken it can affect idling.

Catch tanks are often fitted to allow the removal of the PCV system. Doing so will stop the oil vapour contaminating the inlet tract and fouling the valves. Whether or not the engine gets "thrashed" it will stay cleaner plus the fuel mixture is not effected by the contents of the crankcase.

On systems where the PCV system is retained a catch tank will help to "filter" out the heavier oil particles, better ones try to work like a Dyson vacuum cleaner. land rover's own TDi engine has a cyclonic oil separator.

Thing is as observed they are only of limited effectiveness and similar success can be had using a flame trap, although these do suffer from blockages if not cleaned.

As for whether TDis breath more than V8s, it has very little to do with CR. The higher CR demands a "stronger" engine in any case. The piston ring blow-by is driven by combustion pressure. Sure, But CR is not just the number as "Static" static CR is not really important it is the Effective CR that gives us our combustion pressures. and Combustion pressure as an average is higher in a Diesel than a Petrol, This average is mainly due to the fact it can run a MUCH higher "effective" CR

This gives us our big Diesel torque numbers.

The reason breathing is more noticeable on a diesel is the lack of inlet vacuum to consume it, TDis use the turbo inlet for this which serves to make the turbo quite filthy. You are mixing up "Closed throttle vacuum and "overall" vacuum! A Diesel is running 100% at effectively WOT but without the fuel, it is this that helps give Diesels their great efficiency, Overall Vacuum and certainly the vacuum seen by the PCV valve is extremely close between the two types, remember that most petrol PCV systems also take their air from the atmospheric side of the butterfly. Basically identical systems!

Without wanting to sound rude here, there are several mistakes in your text, I have outlined them in red.

The turbo etc ends up quite filthy on a Diesel due to the "extra" piston blow-by and therefore oil contamination encountered on Diesel engines. Why else do you think we get such black filthy oil in diesels compared to Petrol engines if the combustion contamination was the same? And don't tell me because all diesels are made with crappy rings ;o)

Black dirty oil = black dirty deposits on our bits :o

Again. Please don't take this as an attack, it most certainly is not!! your post and comments are very interesting.

Lara

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Ok, I'll try and put that straight.

The the Ford PCV system did have a breather in the filler cap, the scrubber inside it allows air to be drawn into the rocker box on the cross flow and the cam cover on a Pinto. The air circlulation diagram is in the manual but I don't have it to hand. The scrubber limits the amount of vacuum, if you blocked the filler then the vacumm would rise to that present in the inlet manifold. If the engine were still in my MkII I could show you, the engine is a factory rebuild and certainly was in very good nick. If you put the palm of your hand over the filler it would pull the skin (slightly painful) and begin to draw air in through the front oil seal. The amount of air drawn through the system is controlled by the diameter of the pipes and the valve. On some cars an anti-run-on valve was added into the circuit to allow extra air into the inlet manifold via the same pipework when the ignition was witched off (BL fitted the same valve to the Metro).

So maybe I didn't explain it properly. The PCV system is intended to more than keep up with piston ring blow by and prevent the oil vapour and blow-by being vented to the atmosphere, except possibly when flat-out. At the time I understand the concern was as much about contaminating the road surface as the environment at large. More modern engines can't have the vented filler cap because limits on indirect emissions are much much tighter, instead the PCV system vents in to the atmoshperic area of the inlet or the air filter housing but is still connected to the plenum chamber. Where the Ford system differed form the Rover V8 system is that the connections to the plenum vacuum and atmoshperic air are T'd together and share the same connection to the engine rocker on the V8 whereas on the Ford they certainly used to have different connections and there was a definite draught through the engine.

Diesels, hmm, whole different issue. Until the introduction of the "clean air act" diesels none of them had inlet manifold vacuum, or more correctly plenum vacuum, because there was no throttle plate. So unless you have a vacuum pump there is no way to absorb the piston ring blow-by with a PCV system, there is no positive ventilation. On turbo engine there is perhaps some vacuum ahead of the turbo when the engine is on-boost but I suspect the location of the breather elbow is more about not allowing the indirect emissions out to atmosphere.

Diesels by their very nature have to be much stronger, diesels have stronger rings than petrol engines as a rule and this is perhaps one of the reasons they are mechanically not able to rev quite so hard, typically another is the longer stroke.

The piston ring blow by in a diesel has a different content, it contains far more soot which is the big reason it turns the oil black. Now whilst it's true that during compression a diesel engine will have higher cylinder pressure than a petrol it doesn't always follow that during combustion the same will be true. Brake Mean Effective Pressure is the technical term for it and it can be calculated from the brake torque, speed, numer of cylinders, bore and stroke. If I looked hard enough I could find the formula but I'd sure you get the idea.

Diesel efficiency, bit of a myth there. True the lack of "pumping losses" (the energy wated by the engine fighting the throttle body) does count very slightly but diesel fuel gives up around 42Kj/Kg whereas petrol releases 44Kj/Kg*. The reason you get more MPG has more to do with the density of the fuel than any other single factor.

I'm not sure what you mean by Static CR and effective CR. I only know CR as a measure of the combustion space (or volume thereof) as a fraction of the swept volume (plus combustion space) On a perol I'd expect anywhere between 6:1 to 11:1 and a diesel around 19:1 for a TDi and 23:1 for an indirect normally aspirated engine. So are you talking about working pressure?

I dunno, I'm off to bed :closedeyes:

*Dr Richard Stone "Internal Combustion Engine Theory"

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That still doesnt make any sense.

The scrubber in the oil cap is there to remove as much oil from the escaping crank case vapours as possible. Engines DO NOT breathe in thru the oil filler cap, Remove the cap on any running engine, and you'll find a steady stream of crankcase vapour exiting the hole.

The breather system connects the crankcase to the inlet, so all that blowby can be burned off rather than dumped out to atmosphere. On turbocharged engines, petrol or diesel, you cant connect the breather to the inlet manifold directly, as that would pressurise the crank case with boost. As such the breathers are routed to the turbo inlet instead.

Diesels dont rev because the fuel doesnt burn very quickly. If you tried to push it much past the usual 4500-5000rpm limit, the fuel would still be burning when the exhaust valve opens, and you'd melt valves/turbines etc.

Effective CR, or dynamic CR, is the CR the engine sees when running. Static CR assumes 100% cylinder fill. Due to inlet valve opening times and cam lift, a n/a engine will almost never see 100% fill, so its dynamic CR will be lower than the static. A turbocharged engine on the other hand can achive much higher than 100% fill, so the dynamic CR will be much higher than the static. This is why most turbocharged engines have a lower static CR, to ensure that when its running at 150 or 200% cylinder fill the dynamic CR isnt high enough to cause Bad Things to occur.

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Hi Richard,

Slightly more understandable but just to check my understanding of your Ford PCV description. You are saying the vacuum on the filler cap was with the venting pipes "Still connected"? if so I agree this is quite feasible!

I totally disagree though with your theory of Diesel efficiency being to do with its density!

As the energy BTU/lb or Kj/kg of diesel is very similar to petrol, Approx 19000 compared to 19300btu depending on ingredients which varies more for petrol these days than Diesel, so to be generous we are talking 1.58% here! not a staggering improvement really!

lb for lb will show you that it has almost nothing to do with the density of Diesel fuel.

That is why at WOT power for power there is not much in it fuel efficiency wise from engines of the same size / mechanical and volumetric efficiency rating. however at part load etc and general driving round town conditions they are vastly better due to the reasons quoted, and also due to the fact that in general and other than racing use diesels are always in a "Lean burn" condition and regularly run with 50% or more excess air. A condition not advisable in a spark ignition unit. It is though a little hard to compare the two as they are never "like for like"

I am very well aware of BMEP and know the theory quite well. You will also see that a Diesel at lower revs has a very high BMEP and this directly relates to Torque.

Theory as follows. BMEP = (Torque x (12 x 33,000 / 5252)) / (Displacement in Cu/in x 0.5-for a 4 stroke)

So you will see that an engine with more torque will have a better BMEP than one with less. (Size for Size)

*note, the 12 x 33,000/5252 is normally abbreviated to 75.4 but I wrote it as above to show workings.

As you can see that higher torque = higher BMEP you are actually telling me I'm correct.

This statement below is fundamentally wrong which ever way you read it!!

"Diesels, hmm, whole different issue. Until the introduction of the "clean air act" diesels none of them had inlet manifold vacuum, or more correctly plenum vacuum, because there was no throttle plate. So unless you have a vacuum pump there is no way to absorb the piston ring blow-by with a PCV system, there is no positive ventilation. On turbo engine there is perhaps some vacuum ahead of the turbo when the engine is on-boost but I suspect the location of the breather elbow is more about not allowing the indirect emissions out to atmosphere."

Vacuum is not a condition of which fuel is burned!

Vacuum in a Diesel or in a spark ignition engine are identical all other things being equal!!

The inlet manifold vacuum below the butterfly does change yes but not engine vacuum total! Both suck just as hard from their relevant air filter boxes!! Turbo or not!

Let me explain the theory.

Both engines are 2000cc 4 stroke engines.

Both have the same static CR, (not that it matters here much)

Both have the same Volumetric efficiency, (for arguments sake let us pretend 100%)

One revolution = 1000cc sucked (or blown if you really want to be pedantic) into your engine!!

It is not until ignition that the engine finds out what it is! and reacts accordingly. (simplified here ;o))

Lastly,

Please don't go quoting your Dr's degree expecting me to fold flat and collapse!

A degree is a piece of paper! We all have them, just as I have my Engineering degree, it is also a piece of paper and I know now a trillion times what I knew when I got that 25 years ago. And most of my non degree colleagues know more also!

It does not stop me being wrong and it does not mean I know any more than the next man. that is the fun of life! You never know who you are talking to or what they know!

You only ever "know" that what you know is never enough!

When you say on one hand "Dr" AND "Internal Combustion Engine Theory" And on the other you are not aware of "effective Compression Ratio" then I have to ask whether this was a quote from something you read or are you actually a DR of internal combustion theory?

I really do not want to sound condescending but this really is basic of basics here! I find it extremely hard to believe you research internal combustion engines without knowing this!

The "Effective CR" is as follows and put very simply,

An engine with a static CR of 10:1 that only fills it's cylinders by 50% due to poor efficiency etc has an "effective" CR of 5:1

As can be seen, you can give your poor volumetric efficiency engine a high static CR and have the same effective "actual" CR as one with a lower static CR but better volumetric efficiency. Therefore this is the "ONLY" CR figure that is relevant to anything!

As we know and can test and can see above,

Diesel engines have extremely high cylinder pressures compared to spark ignition engines of the same type and size etc. this is generally why they breath more!

The main reason Diesel engines have difficulty revving is for the following reasons, in order of importance.

1.As Aragorn states quite correctly, The flame propagation rate of Diesel during the injection. (if it does not burn fast enough you can not inject it without causing other problems) this limits #2 below.

2.Injection time available, You need to inject the fuel at the correct time in order for it to burn and reach it's peak cylinder pressure just before TDC otherwise you end up with a poor efficiency and over heated EGT etc. as you can imagine, these are serious limits (the development of modern fuels and extremely high pressure injection systems has given us a big increase in high speed diesel engine availability in recent years but we are still limited)

3.Weight of internal components to withstand the higher cylinder pressures compared to petrol engines.

4.Stroke etc is currently one limiting factor but a diesel does not "have" to have a long stroke!

Enough for now, I need to do some more work!

Lara

Engine development, thermodynamics research, mostly but not always related to the internal combustion cycle have been my life for the past 30 years, Full time working and hobby! and I can also get things wrong sometimes! even without my degree ;)

Theory and Practice.

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Hi again Richard,

Just re-read my reply and just want to say that my response was difficult to word and I mean no disrespect what so ever.

I am just trying to put over my findings from many years hard dedicated work and learning.

I too may have made mistakes but am fairly sure there are no serious ones above!

(other than the odd spelling) :lol:

Best regards,

Julian

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