F7P breather system

[Nick Read]

Help needed from anyone whos done a stripdown of a valver lump! Im about to hook up a carbon airbox in place of the original, but Im gonna have the two breather pipes just hanging there instead of going into the back of the filter.

Now one of them I can see is the big pipe that comes from the middle of the rocker cover, so the oil vapour is supposed to be drawn out and burnt off in the engine. Now what would be the best option out of these (and give reasons)?

a) Stick a breather filter on the actual rocker cover and get rid of the pipe entirely.

b) Keep the pipe and put a breather filter on the end.

c) Put the end of the pipe into a catch tank vented to the atmosphere.

d) just extend the pipe and let it hang down dripping oil under the car.

Second question is this - what do I do with the other smaller pipe?

Third question - surely there must be other breather pipes around somewhere, not just above the cams - but where?

 

[Pysco]

If you just leave it hanging then there is no suction to draw the vapour out, leaving it hang means if air is being drawn in then crap can get sucked in too, if you put a filter on it you risj is getting clogged with oil and then the block cant breath correctly which is bad news.

Well one of the pipes goes to the ISCV so Id put a crankcase filter on this, the otherone is the pre-throttle breather. I think the best system would be to block off one of the breather pipes on the rocker cover and then fit a proper breather system to the other with a vapour seperator and a return to the sump. This is what the guys at Hough and Sons recomended anyway.

 

[Captain Slarty]

fit them back to the same area they came from m8.

ie, mod the airbox or intake.

we used to hook them up to a drip container, but it doesnt allow the crankcase to breath correctly.

Even on the turbo its routed back to the intake (pre-boost)

Its an important part of airflow through the unit.

Joe.

 

[Nick Read]

Well yes there are two breathers from the rocker cover - one smaller bore one that goes straight across to the manifold and one larger bore one that goes to the back of the filter.

I know that the theory is that the manifold vacuum draws the vapour out but surely it can still do this with only the smaller bore connection? Is there anything particularly beneficial about burning oil in the cylinders instead of fuel and air? In other words which is more important - running a breather system which draws out the vapours efficiently or running a system that is not so efficient but also does not mean you have to burn the vapour?

 

[Captain Slarty]

Hi Nick, you arent burning the vapour (I presume you mean oil vapour ?) as it connects via an oil seperator either machined into the R/cover or via a filter.

The more cylinder pressure you run (ie nos / turbo etc) then the more chance of crankcase pressurisation you run too (from ring blow by). The size of pipe is for a reason, ie - to flow freely. Without this you will be prone to oil sooting and leaks (ie blown seals)

Where does the smaller pipe connect to ?

Joe.

 

[BenR]

Capt, can you help me with mine then!

On my XR2 the block berather is blocked off from the factory, the only breather system is from the oil cap. 3 outlets, one blocked off from factory. One to the airbox and one i have no idea about, it was connected to the blocked cap outlet when i got it, but the cap kept blowing off and the dipsick kept blowing out.

It now vents to under the cat vai a long pipe and its solved the probs, no weird judders, no extra consumption of oil, no blow bys etc etc.....no excess oil leakage........its stumped me!



Quote: Originally posted by SimonNOS on 21 October 2002





If you just leave it hanging then there is no suction to draw the vapour out, leaving it hang means if air is being drawn in then crap can get sucked in too, if you put a filter on it you risj is getting clogged with oil and then the block cant breath correctly which is bad news.

Well one of the pipes goes to the ISCV so Id put a crankcase filter on this, the otherone is the pre-throttle breather. I think the best system would be to block off one of the breather pipes on the rocker cover and then fit a proper breather system to the other with a vapour seperator and a return to the sump. This is what the guys at Hough and Sons recomended anyway.

SI!!!!!

you go to Hoffs!!!! i go there too, a mate lives in ropley and hes always hammering it round there. Johns a cool guy and when im down ther im usually int eh shed where they do all the performance pug cars.........

if your down there, we can meet sometime!

 

[Nick Read]

Hmmm, AFAIK and going on what the Haynes shows and what I remember seeing under the rocker cover, there is *no* oil separator there... the oil vapours really are drawn out of the larger bore pipe (theres a restrictor inside the rocker cover outlet) by the connection to the back of the filter, ie just upstream of the throttle body. While the engine is idling the smaller connection (direct from rocker cover to inlet manifold) would be the only breather pipe operating; the vacuum there would draw out oil vapours from inside the rocker cover - the only place for these to go is into the cylinders to be burnt. As soon as you open the throttle, the larger connection also becomes operational, and draws oil vapours out of the rocker cover, along to the inside of the air filter, where it mixes with filtered air and enters the manifold past the throttle, and from there into the cylinders to be burnt.

I think the idea is that the whole time, these breather connections to the inlet tract, both upstream and downstream of the throttle, are creating a partial vacuum under the rocker cover to scavenge the oil vapours out and burn them. Certainly these two pipes are carrying oil or oil vapour because an inspection of them on any 16v will reveal that they are oily inside and the larger one drips small amounts of oil inside the air filter occasionally.

So what Im really saying is could I replace the vapour burning system (which is how it works at the moment), with an external oil separator? The larger pipe would connect to a tank - the top of it would vent to atmosphere through a small breather filter just to make sure nothing could find its way inside except oil. The bottom would have a drain to feed the liquid oil back into the engine somehow...

 

[BenR]

here is an easy fix.....!!!!

just connect it up as its mean to, i.e. to teh airbox...easy part.....if you dont want to burn all that crap......fit an inline fuel filter from a carbed car. GO to any motor factors andd get one for like 70p and fit it inline from teh rocker cover to teh airbox. They are clear plastic so you can see them get dirty and change them when needed.

no oil on filter but vacuum system still works!!!!

 

[BenR]

oh yeah, an on the 172 you can see the is filty when you take it off.....oil vapour mixed with really fine dust.......

 

[James20VT]

Nick, what carbon air filter is this u have for ur valver? will it work on my williams?

 

[Nick Read]

Good plan Ben I never thought of that! BTW I remember when we were over in France at the track day one of the French valvers there, which was a proper race machine, had a garden hose leading from the outlet on the rocker cover, and across the engine bay into the scuttle panel where there was a tub in there to collect the oil! So maybe theres something to be gained by not burning the oil vapour off.

Anyway it looks like its all worked out then - the ISCV pipe can just be capped with a breather filter so it can still draw filtered air, and the breather from the rocker cover can still be plumbed in but going through a fuel filter.

 

[Captain Slarty]

the original method of venting crankcase pressure was via a metal woven fiter., the guys with the dcoe carbs in the 70s found that it was impractical to vent to a carb as no common air passage was available between the chokes, so they led the pipe to a catch tank...

that doesnt mean, just cos, it WAS used, that it is beneficial.

Your assumptions are based (Ben n Nick, me thinks, on a theory that this crap or oil in suspnsion, will be a power zappa... it wont, firstly, if there is oil (a blue black/ haze) suspended in the air, then the engine is experiencing blow by (combustion gassess passing the rings and pressurising the system) its basically screwed, and the power lost by the blow by is magnitudes more than any power lost via this suspension, it is also an efficiency aid if designed into the system, the resulting dispersal is better in the plenum due to a hot / cold mix...

Your engine is designed to operate with a free flow of air through it, it cools the internals and oil, it prevents sooting and pressure buildup that the decending piston has to overcome...

putting it into a crap tin is one of those tricks that have become sorta urban legend in the arena of performance, or, as appears here ?, that to do so is acceptable in terms of lass / gain coss it used to happen (I certainly used crap tins on kent engines, many times, cos I had no other practical choice running side-drafts.. had I had a choice, I would ALWAYS vent the engine as it was designed,

It CANNOT hurt anything, and can be detrimental, less power, more wear, worse economy - as the midrange cruise is when most circulation occurs - this is part of the fueling and ignition map too.

Nothing to gain, plenty to lose



Joe.

 

[Pysco]

Ben, yeah I go to Hoffs, going there in the next few weeks to get my NOS fine tuned.

 

[Nick Read]

Fair enough Joe, thats what I needed to know, not really being an expert on breather systems. So what I seem to be picking up is that I definitely should retain the breather connection to upstream of the TB, so that the system will work properly. But Im still unclear about the question of oil being burnt off in the engine. Taking just that issue on its own Joe, if you had a choice of running a car by combusting fuel and air, or running a car by combusting fuel, air and engine oil, which would you choose? Common sense would suggest to me that engine oil is for lubricating, not for burning.

Now if I can put some kind of filter in the breather pipe (following its proper route to come out upstream of the TB) which will catch the oil thats in suspension and allow uncontaminated air to be sucked through still, surely thats a good idea? As long as the vacuum effect of the inlet manifold is still pulling the oil vapour out of the engine, there wont be a problem with just intercepting the oil half way along the pipe and catching it, allowing clean air to be sucked back into the manifold? The only question is, what kind of filter to use which will work on a flow of oil vapour and separate/retain the oil but allow air to pass through? A turbo oil filter has a 25 micron screen and it still allows oil through, just not other bits and pieces. Thats gonna be some humdinger of a filter that Ill need - surely an inline fuel filter wont do it?

 

[Nick Read]

BTW I see your point about blow-by, but the F7P is renowned for using a lot of oil. 1 litre per 1000 miles is not uncommon; F7P lumps that lose a lot of oil are the norm, it must be just the way the lump is designed. My basic question is: is it better to *burn off* the oil or to *filter it out* if this is possible?

 

[tony 16V]

not sure if this will help or not, but K-tec have a oil catch tank breather setup for sale for the R5 turbo. Its might be worth a look on there web site. Im sure it could be fitted to the Clio.

Cheers, Tony.

 

[Nick Read]

James - Im fitting a BMC Carbon Dynamic Airbox (CDA). Matt C has already done it with a custom made throttle body adapter and a standard 16v CDA. Ive got a special short and fat version designed for a BMW 3.0 Z3 which is the only one that will fit in my engine bay the way I want to do it. Still trying to hook it up now though...

Once its done Ill post the results somewhere on here.

 

[Captain Slarty]

Hi Nick, yes , a fuel filter WILL NOT DO.. lol...

Its not really a case of burning oil vapour... firstly, oil does not form a long lasting suspension in air, due to its mass. that is the job of the separater

the thing that needs to be considered is the oil seperation built into the engine. (and you WILL have it) The main methods are either a machined channel of baffles giving a large surface area and disruption to the air flow to cause sepeartion of particles onto the metal surface. For example, the 172 has a sep chamber built into the cam cover(s). It may be simply the fact that the valve train in the head, and layout of such, causes an adequate baffling effect and separation on its own. This is quite common if head vented (as in the F7 series, the older engines, ford Kent etc, were mainly fed from the crankcase and needed a mesh filter to act as a surface area expander.

In other words, you will have adequate filtering or separation, built in.

It is certainly possible to add an external unit as on the turbo, the reason for this is a considerable increase in pressure due to blow by on boost, may well allow some oil particles to pass out of the engine, the only sensible feed for the trubo is the atmospheric side of the induction, but we need to avoid any excess oil deposits on the turbo comp wheel area, so, an external seperator is used (simply a baffled tank with a return to the block)

The way to tell if you NEED an external unit is simple.. check for blue smoke on full chat, if you havent got any, its fine.

There would be no loss of power without a resultant oil burn (the blue smoke being the indicator) The oil burning would reduce the octane level of the fuel resulting in lack of advance on a knock sensor equipped system, or detonation on a non knock enabled system.

If you aint VISIBLY burning oil, you dont need to worry about it, but do need it fitted to the upstream area of the tb.

Joe.

 

[Captain Slarty]

Oh, Nick, re the oil usage on a 7p, it will certainly NOT be from the recirc, it will simply be piston bore clearance - ie - the oil is being burned by going UP the bore, not down as from recirc.

You caould even consider that better venting could reduce this somewhat as it is crankcase pressure and clearance that causes this phenomina.

Older style engines were built with pistons made from materials that were commercially available at the time (within costs).. the expansion rate of the piston over its operating range is not as efficient as more exotic modern materials. Indeed, if you were to fit forged pistons, these would probably, not only rattle when cold - due to the necessary clearance, but also increase oil consumption considerably.. thats the nature of the beast with forged jobbies, the decreased seal is made up for by the increased power that can be safely handled (with appropriate mods)

again, the oil usage is from the bottom, not the top..



Joe.

 

[Nick Read]

Gotcha - that all makes sense. But just out of interest - lets say there was a significant amount of oil in the vapour and you wanted to get it out, what kind of a filter could you use to remove it and allow clean air to pass through? Would that even be possible? Or would you be better off trying to condense it off, maybe by drawing the vapour through a very cold matrix like a radiators fins, where the oil would condense and come out of suspension and the air would pass through?

 

[Captain Slarty]

Hi Nick,

no, no condensing needed etc, its simply a relationship to surface area, ie, the more changes of direction the air makes (prior to the inlet) over metal surfaces (as much as possible) then the oil will be redeposited back to the surface of the metal. It could even be a simple catch tank with woven wire in it (note - NOT wire wool which will breakup and enter the inlet - dont ask me how I KNOW that lol !!!)

Baily motorsport do a superb range of prefiltering catch tanks to do just this.

They are made of ali with many internal baffles to increase surface area and direction change.

Joe.

 

[BRUN]

Nick, what about the mini glass fuel filters demon tweeks sell, would one of those not do it, i think there on the same page as the power boost valves

 

[Captain Slarty]

Brun, m8. you CANNOT use a fuel filter...Oil will block it, it is designed to catch crap in the fuel, not to seperate the oil.

Joe

 

[Alex M]

Have you all considered that a tiny amount of oil in the inlet charge might not do a lot of harm, and might even be beneficial. We know two strokes get all thier lubricating needs from the oil contained in the fuel mix, and that is fine as thier is no complex valve train needing lubricating. However in these days of lead free fuel (lead was a good valve lubricant) perhaps a little oil vapour might assist in this manner. Then again one of you might point out a hole in this, as I am not sure myself.



Why not a have a catch tank but another hosing running of this to upstream of throttle body. Then given the weight of the oil most of it will drop to bottom of tank, but airflow will not be affected.



Alex M

 

[Captain Slarty]

lead was a good valve SEAT protector, but is no longer needed as the design of the components are up to standard, also, the lead replacement addatives in fuel work very well. 2 strokes dont have valves or seats as the 4 stroke does.

So, there is ABSOLTUTELY NO NEED TO ADD OIL to fuel in any way..

Oil added to fuel in sufficient quantities lowers the actual octane rating too !!

As for the tank with the hose to the upstream tb... that is EXACTLY what we are discussing m8 lol..

Joe.

 

[BenR]

ok, with it now!

but what should i be running!?

on my kent engine, there is no place for me to put the breather pipe onto!

the brank ventilation one is blocked off from the factory!....what do i do?

im soon to be running DCOEs as ihvae them but not putting them on till teh full head is finished........then the catch tank is the only option if i dont wantot o spew it onto the road as i am doin now.....but nothing comes out.....

and if i were to hold my hand over or near the valve cover then i can feeel a suction from the engine at different throttle openings and blowing at others.....how does the engine work with this!?

How do so many Kents with non DCOEs run with the rocker cover sealed or with no hole at all......can they run on teh crank ventilation alone?...and before you mention it i cant afford dry sump..LOL

 

[Captain Slarty]

Hi dood,

you are screwed on the kent with webers, you NEED to use a simple catch tank. there is a filler cap for the kent with a built in crude seperator and take off, use this.

as for the engine working with it, well, the thing never had good ventialtion from the beginning, the oil soots up sooner, and the block develops a nice coat of gunge over time whatever oil ya use, but it carrys on running fine. You simply change the oil more often, often need an oil cooler too. The cooling system works harder, and the engine wears at a rate that wouldnt be acceptable on a modern unit.

I have NEVER seen a kent (or believe there even is one !) without some form of breather, often a block mounted breather is used, or, as said, the filler cap type, but not without ANY form of venting.

Dry sump.. lol... this is only for 4 reasons...

1, is to allow the engine to be mounter lower in the chassis to reduce the c of g.

2. to allow a greater quantity of oil to be carried to aid cooling and filtering.

3. to minimise or eliminate oil surge and startvation... and

4, to allow better weight distribution by placing 15-20 Lbs of oil at the rear of the vehicle.

non of the above are for venting lol.

Joe.

 

[BenR]

so mine venting out a pipe is ok.....as ther is NO block ventilation as i said.

and the quation regarding the kents was "can they run on carank ventilation alone?"......LOL........

man, maybe i should give it to you to work......

oh, that RR is still in our basement in HK if you want ot setup as the premier tunner in asia......sine nobody there knows anything and they charge a fortune for it.....uprated brake pads......200 quid please....LOL...and they pay for it.

 

[Captain Slarty]

yep, I would be into that, whats the deal lol ???

and, yes, in your case, you dont have any choice .. (the lack of venting !)

Joe.

 

[Captain Slarty]

ps, most of the rally cars with kents in the 70s used a mini windscreen washer bottle as a crap catcher lol... it even came with a clamp to fit it to the inner wing !!.

Its translucency allows you to see the level of oil in it too.. bonus dood !..

there ya go, AUTHENTICITY m8 !

Joe.. lol.

 

[BenR]

cool.....ill no worry then.

the deal.....um, setup a company to rival the best in HK.

The guy i worked with in HK is probably the best in HK, but im amfraid the lack of many specialist tools and a RR tend to mean his work is put to gether great but not setup 100%. I mean, mapping a car on teh road only!

he has loads of contacts in the UK too as he studied here and is the supplier for many top parts.....etc.

But, im yet to see a competent tunner in HK.......ask them a question and THEY look at you witha a blank face sometimes!

setting up would be fairly expensive though, as plemesis rental is huge and cheap is erally out of the way in the new territories!

but once setup, i think it would rock HKs scene and really show what you can and are meant to do.

still, teh cost is such a limiting factor. Think £6000 a month for a premises that can fit maybe 4 cars in and no machenery....ooer..it would be hard, but higer the risk, higher the reward.....you can charge soo much for little things!

a mate paid 250 quid for a 206 GTi TB to have its spindle and plate flattented!!

 

[Captain Slarty]

naw..

what I need is a contract for 3 years, a house, and a profit sharing scheme m8..

look at is as an enhancement to the services offered...

or, do you need a cv lol...

I do agree that the greater the risk, the higher the POTENTIAL reward... but It would be someone elses risk.... and money.. not mine.. I just do the job, and bloody well too lol...

If they want the best, they pay for it.. that AINT being arrogant m8, just 45 years of experience of WHO makes the money and WHO stands to gain by WHOs Knowledge and experience lol..

Joe.

 

[BenR]

true, but were not allowed to offer any services as said, no tunning etc.....no RR even as we built a room specialy for it at teh cost of 10 million and the govt said no......oh well.

and nobody will ahve the money/balls to backup any project of the sort.

You will never get what you want there, things just dont work like that, its always one person tying to screw another.......which is a shame as the palce is nice and so are the people, until they step into work that morning.

An you wouldnt get a house...LOL, a 3600 sq ft apt if lucky with no garage...haha......our 4000sq ft apt cost 24 million last time i heard, which was about 5 yrs ago........nutters, pure nutters......