How to install an oil catch can
I have just finished installing an oil catch can on my car. The instructions are relevant to turbo or NA engines.
After studying the emissions diagram in the workshop manual I decided on the best way of mounting the catch can. First off, find a suitable place to mount your catch can. I found a space between my fuel filter and master cylinder. My catch can is a autopro "type X" brand one, I chose it because it has a very large opening on one end. It came with 2 small fittings on one side, and one large fitting in the bottom. I have mounted it upside down with the large fitting in the top, and blocked off one of the lower side fittings. I filled the inside with grade 2-3 steel wool, to help in filtering out the oil from the air. most if not all catch cans come empty inside, which does squat for filtering the oil out of the air. the large opening cap is at the bottom, and can be unscrewed to let it drain out periodically, It also has a level gauge on the side. Cost about $80.
This picture shows the mounting place of the catch can, this space could still be used, even with a custom manifold fitted, or a twin cam engine fitted.
This picture shows the connection of the hoses.
The PCV valve is mounted in the manifold on the single cam engines, there is a pipe that connects from the front bung on the rocker cover to it in the factory mounting. I have removed that hose, and taken the small hose from the rocker cover and into the side fitting of the catch can. The large hose off the PCV has been routed around the manifold and into the top fitting of the catch can. Care needs to be taken if you rout it in the same way I have in that it doesn't come close to being rubbed through by the accelerator cable, or it'll split open. In the factory system, the PCV is sucked open by the engine during idle, cruising and deceleration, when the engine vacuum is high, this sucks any vapours out of the crankcase and burns them in the inlet. If there is any blowby, it'll force the oil vapours through the bung and into the catch can, filtering the oil out before the air is returned to the inlet manifold.
If I drew the emissions diagram with the catch can drawn into it, it would be between the PCV and rocker cover, acting as a filter. that covers mounting the catch can, and is legal, as it is not venting any fumes to atmosphere. If you have any issues in performance on the track or strip, you can plug the large hose (PCV) on the manifold, and place a small filter on the catch can large hose, but that is not legal for the street.
For the other half of the emissions system, the engine requires some way of sucking in fresh air into the crankcase for circulation, this comes from the hose connection between the rear bung on the rocker cover, and the inlet pipe before the throttle body. Theoretically, there should be no oil drawn from the rocker cover into the inlet via this hose, however we all know it happens, usually due to excessive blowby, or crankcase pressure from high revs. there is 2 solutions to this. First one is to fit a one way valve in line, and connect it as per factory. i have chosen the other route, as i am moving my AFM to right before the throttle and turboing the engine. I have removed this hose connection to the inlet pipe and re routed it down near the airbox. in the airbox is a filter, and a one way valve. the one way valve prevents oil vapour being blown back along this hose into the inlet system, and the filter prevents any oil vapour getting past if the valve fails, and also from any dirt or other crap being sucked into the crankcase.
First i needed to construct the filter, there are many ways to do this if you think carefully about it, however in its placement, it is not legally needed, as there is already the main airfilter in place. you could quite reasonably just put a hose bung directly into the side of the airbox. I used the spare hose fitting that i removed and plugged from the catch can, and found a large nut with a flat base that it would screw into, next, i found a threaded piece of rod, and welded a nut to the bottom of it, I ground out both sides of the nut, and half into the threaded bolt, to allow air to pass around and in once it was fitted in place. if you could imagine, it is now a 'V' shape on the end of the rod, with the point of the 'V' forming into the rod, like so, >---- That whole assembly was then welded onto the large nut and the base cleaned up
Next came the filter. I used an Air filter from a Victa 2 stroke mower. you can get these from just about any hardware store for about $3. the only requirement was to drill a hole in one end for the threaded rod to go through. Here is a picture of the complete filter assembly not fitted to the airbox.
I decided that the best place to fit it into the airbox was against the front wall nearest the headlight, under the filter.
If you had a small enough drill, you could drill the hole without removing the airbox, but I needed to remove mine. Here is the hole drilled, you can see that it needs to be on the flat part, between the structural ribbing. the hole is about 22mm big.
Next I fitted the filter into the hole. I also used a rubber o ring to seal between the big flat nut, and the side wall of the airbox, if you look carefully, you can see it. The filter sits on the inside of the airbox, and the nut on the end of the thread to secure it all, make sure its centered over the hole, or it'll leak unfiltered air into the inlet system. Maybe a better way to mount it would be with araldite? or some other epoxy resin.
I haven't got pictures of the hose that comes from the fitting, but I used an offcut of the old PCV hose (the 90 degree bend bit) so it was pointing into the engine bay, the one way valve was put into that, allowing air to be sucked into the engine only, and from the valve back to the rear bung on the rocker cover. The old connection on the inlet pipe was blocked off.
Discussion[edit]
Flubba86[edit]
Mate, I have spotted a flaw or two in your setup. Your rear-crank case inlet is now sucking air from BEFORE the AFM! This means then when the PCV is active and open, usually in precise air-flow conditions like idle and cruising, then you are having air enter your engine which has not been metered by the AFM, which throws your mixtures way off. Also, we are not talking about just a little bit of residual air here, the PCV is quite a big air-source and actually constitutes about 50% of the air taken in during idle and cruise situations. This is why the stock setup had the air being drawn from just before the throttle body, because that air had been metered and was about to enter the engine anyway.
As with the one-way valve... are you implying that you have a valve on the rear-rocker-spout-to-airbox-line which prohibits air being blown back down the line, and only opens again when there is suction (ie. pcv conditions) on that line? If so, that is a recipe for crankcase pressure overload. Picture this... you are having a spirited drive, your throttle swings open to low-vacuum conditions, the PCV valve swings shut (because its meant to do that on low-vacuum situations) and thus your catch-can is rendered useless... now on a stock setup, a venturi-induced vacuum would be created on the rear-spout because of the air rushing through the intake pipe, and thus pull the excess air out of the crank-case that way (like a reverse pcv setup). This kinda happens on your setup, but im not sure if the velocity of the air through the lower section of the air-box would be great enough to create a reverse suction on that line, plus you mentioned you put a one-way valve on that line so you cant suck air in that direction anyway! So... your PCV is shut, your rear-spout is shut, you are fanging your engine, blow-by is being created in the crank-case, pressure builds up in the crank case, dip-stick shoots out or main seals blow out. Bad bad bad.
Gemi Coupe[edit]
yea, i understand what your saying flubba, But, What about all the people who move their AFM to just before the throttle? they would have the same running rich unmetered air problem. I have a o2 display in my dash, and in the last week or so of driving around like this, i haven't noticed it get any richer, couldn't tell you about my fuel economy though, i haven't filled up yet. Also, with the way its all connected, (dont mind my work of art Roll Eyes)
the catch is sealed off once the PCV shuts, as you said. but the PCV would shut anyway even if the can wasn't there. At that point ANY pressure buildup in a standard setup would simply releive pressure out the rear rocker cover bung, and straight into the inlet. I guess if you really wanted to you could connect that through a seperate catch can to try and filter that too. But in the way its set up on mine, any pressure buildup in the crankcase would force the PCV open and vent through that. In a NA setup, the pressure in the inlet track that would need to be overcome, would be just below atmospheric, so it wouldn't take much at all. the rear bung sucks fresh air in due to the fact that the crankcase fumes being sucked into the inlet creates a low pressure situation inside the crankcase, Its position for that part of its job wouldn't matter where it is, so long as its sucking clean air.
I can see how it becomes an issue on boost, and im still thinking about how to overcome that. A solution will come to me soon. maybe i'll trim down the dipstick seal, and use it as a 'saftey valve' However as a point of note, how long in street conditions do you stay on boost? a few seconds? then change gear and the PCV opens, then a few more seconds, then change gear and the PCV opens, then cruise coz your at the speed limit and the PCV stays open. when you look at the design of the valve, and the 'general' driving conditions your engine would encounter on the street you'll notice that the valve actually stays open for a very large range of driving conditions.
Flubba86[edit]
Yeah you're right, with a n/a setup the excess pressure will simply push the pcv back open again because of what you said, low pressures in the manifold. And what you mentioned about using a second catch can, between the rear spout and the air source, is what I have considered many times, but it would be hard to implement due to the fact that the rear spout is sometimes sucking, and sometimes blowing, depending on whether you are in vacuum or acceleration conditions.
Im still not comfortable with the fact you are sucking in unmetered air through the pcv. Every time I have had even a slight vacuum leak in my engine, it would run rough. The pcv sucking air from an unmetered source is just like a MAJOR vacuum leak, and will run heaps lean, to the point of nearly stalling. And that cant be good for your car. I am guessing you havent noticed it because your oxygen sensor might be in good condition and is catching this error and correcting it.
Every person I know who has done the relocation of the AFM to just before the throttle body, has used an XF throttle body in conjunction with the mod, because the XF throttle body has two spouts in its body just before the throttle butterfly (so after the AFM), and you use one for the idle-air source and use the other for the rear rocker cover source, because these two points are now the only places on the inlet tract to get metered air from.
My current setup is what I would call correct for a turbo car, but not legal. Firstly, I have an aftermarket plenum, and zero PCV valve, there isnt even a provision there for one. I have small breather filter on the rear rocker cover spout (for sucking in fresh air) and the front spout is connected, via a catch can, to a spout I have placed just before the mouth of my turbo. My AFM is in my cooler pipes just before the throttle body, so all of this is working outside the zones of metered air. On idle, there is very little suction through the turbo and almost no movement of air though the rocker cover. If there is any crankcase pressure, it is immediately pushed up thought he front spout and into my turbo inlet, just more air to be combusted, and very little oil vapours because of my catch can. On strong acceleration, when my turbo gets a spool up, the air being sucked through the inlet is quite massive and it puts a suction on my front rocker cover line, sucking air through the rear breather, collecting oil vapours and blowbys in the rocker cover, out though the catch can, and into the turbo. The only problem I have with this setup is that there is no vacuum on the rocker cover during idle, so my ticking is a little bit louder, and I can hear the cam spinning around in its bearings etc. But as soon as there is any acceleration, the vacuum is pulled through the crankcase as it should be. so the pressure buildup in the crankcase wouldn't be much, unless your engine had some serious blowby issues, which would need to be rectified anyway. as i said in the first post, for track/strip, you would just block off the PCV and put an open vent on the top of the catch can, perfectly legal on the track and no crankcase pressure issues.
Compiled by: Gemi Coupe
